ABSTRACT

     Celestial bodies like the Moon and asteroids contain materials and precious metals, which are valuable for human activity on Earth and beyond. Space mining has been mainly relegated to the realm of science fiction, and was not treated seriously by the international community. The private industry is starting to assemble toward space mining, and success on this front would have major impact on all nations. We present in this paper a review of current space mining ventures, and the international legislation, which could stand in their way - or aid them in their mission. Following that, we present the results of a role-playing simulation in which the role of several important nations was played by students of international relations. The results of the simulation are used as a basis for forecasting the potential initial responses of the nations of the world to a successful space mining operation in the future.

---

     The article is composed of three parts. The first section depicts the rationale for space mining and describes the current and future technological state of this field. In the second part, we portray the simulation. We analyze the political outcomes which should be addressed by the international community in the third part. We then conclude with some lessons for further discussion of potential mechanisms to mitigate the primary dilemmas and concerns which would be raised once the technology becomes a reality.

---

3. Simulations and roleplaying games as a forecasting method (second part)

     Roleplaying and war-games are a widely used method for forecasting decisions by two or more parties in a conflict. The origin for these methods stems from the 18th century, when officers and generals in the Prussian army utilized Kriegsspiel [“wargame”] to practice strategy and tactics. The Prussian victory in the Franco-Prussian war in 1871 was partly attributed to their use of wargames to provide superior training of their officers. Since then, roleplaying games have become an accepted method for forecasting the way in which conflicts are resolved in business, law and politics. Roleplaying is also used to train professionals for future events and cases; this practice is particularly relevant in the legal field.

     Roleplaying games have shown their merit, particularly in cases in which groups have conflicting and complicated wants and needs. Often in such cases, it has been discovered that even though negotiators can find a zone of agreement, they still fail to reach decisions that are accepted by all. It turns out that expert negotiators often do not realize the emotional and personal needs, desires and difficulties that shape the decision making process. Roleplaying games do not suffer from this oversight, since the players are asked to fully emulate a certain character or side, and the needs and desires of the characters are automatically absorbed into the game's decision making process.

     Roleplaying games are also of particular use when trying to forecast the impact and consequences of large changes. Experts have an advantage in understanding the results of small changes in their field of expertise, but they lose this benefit when confronted with major and disruptive changes that span many fields. Roleplaying games can provide a different venue for forecasting the results of such cases: the actors react to the changes by consulting with each other in real time, and providing solutions that rise from the group as a whole.

---

4. The scenario and process of the space mining simulation

     The scenario was designed with the help of space professionals with backgrounds in space engineering and technology, space politics and international law. The primary purpose was to produce a general, workable scenario that would serve as a starting point to trigger processes and trends in the international system. The simulation was conducted as part of a graduate class in Space Politics at Tel Aviv University, during the spring 2014 semester. The simulation game was presented to the students at the beginning of the semester. About 20 graduate students from the graduate program for security studies and the graduate program for diplomacy participated in the simulation. It should be noted that as often happens with graduate students in Israel, some of them had professional backgrounds in military service, the diplomatic corps, etc.

     The initial goal of the simulation was for the students to get a sense of the variety of issues related to the politics of space: political economy, environmental issues, power and security of states, cooperation, diplomacy and international relations, technology, international law, etc.; raise their awareness of actual political dilemmas; and enable them to have at least some first-hand experience in the related process. In conducting the simulation, we made no pretense that we were going to encompass all the issues related to space mining. Rather, the objective was to raise awareness of some of the major issues involved and encourage creativity in searching for potential solutions.

     The scenario began in the year 2035, in which Earth's population has grown dramatically, and alternatives must be found to the dwindling natural resources that are essential for the continued growth of the global economy. In an attempt to deal with this challenge, a number of private companies and national space agencies from the U.S. Russia, China, India, and Japan, have been working for several years on developing technologies to extract minerals from space and ship them back to Earth. In January 2035, “Human Welfare”, an American based company, is the first to successfully mine minerals in space and transport the cargo back to Earth. The shipment contains large amounts of gold and platinum, which are only a small part of the riches that the mined asteroid contains. Processing enterprises need to be established to transform the raw minerals brought to Earth into usable material for global industries. The technological demonstration, together with an optimistic business plan showing economic viability, produces a new economic and technological reality that has great political and economic implications. The immediate consequence on the global market is a dramatic decrease in the value of gold, the price of which fell by 50% on the World Mercantile Exchange Market. In light of these dramatic developments, the UN Office for Outer Space Affairs (UNOOSA) announces that the annual meeting of COPUOS, held every year in June, will be devoted to the issue of space mining. The meeting will take place in the form of open-ended consultations at UN installation in Vienna. Member states and observer states are invited to express their opinions and discuss the matter.

     Several factors contribute to the reliability of the forecasts produced by simulations and roleplaying games. In the experiment described herein, we made use of each factor, as follows:

4.1. Actors must take their role seriously

     It is believed that actors can largely be ignorant regarding the dispute in question, as long as they receive the relevant reading material on the subject, and take their role seriously. For that purpose, we asked graduate students to take part in the roleplaying game at the beginning of the semester, while the actual game was played at the end of the semester. First, each student was assigned to a country that he or she was to represent in the simulation. The first task, which lasted for two weeks, was that each student had to get acquainted with the overall characteristics of the country he/she represented: its economy, geo-strategic environment, political issues and so forth. Students were also asked to learn about the country's space policy and activities. Based on this information, in the second task, the students had to define and analyze their country's primary interests and considerations, and evaluate and asses the approach it would take regarding the new technological reality presented in the scenario. For this task students had four weeks to prepare. The final assignment was to prepare the actual simulation game, which was played at the end of the semester. It should be noted that from the beginning, students were aware of the fact that their final grades depended on their performance in all stages of the simulation game, including preparation for it. Thus, most of the students seemed to take their tasks seriously.

     To help students prepare for the simulation and specifically for their role in it, they were provided with a list of issues and questions to guide them in thinking about the various aspects of space mining and its potential consequences for world politics. For example, students were encouraged to think about the potential impact of space mining on the international balance of power, and whether they expected the present balance of power to change? Will the status of some nations change? Which countries would be interested in creating their own mining capabilities and companies, or at least directly benefit from the new developments? Which governments would object to space mining and act to stop or disrupt it? What can nations do to avoid or minimize potential damage to their economies?

4.2. Realistic environment

     The players need to feel as if they really were the characters they were supposed to be. We simulated the 78th meeting of UN-COPUOS. We provided each player with a flag of the nation they represented; as moderators of the event we conducted the game as though it was an actual meeting of the committee in question. The simulated discussion was divided into three parts. The first part began with a statement by the chairs of the session (played by the authors of this article), who called on the representatives of the different countries present to take responsibility and act together for stability and peace on Earth for future generations. The chairs then invited all the representatives to participate in the discussion. Students then delivered short national statements prepared in advance on behalf of their countries, in which they explained the country's approach and perspective towards the new reality. Among the issues raised in these statements were global challenges, global opportunities, national concerns and national objectives.

     The second part simulated a recess in the formal meeting. During this recess, the representatives had the option of approaching and interacting with other representatives, in order to discuss various ways of addressing the issues raised in the statements. The third part of the simulation was another formal session conducted as an open discussion in which the representatives commented on each other's statements. They raised potential mechanisms to mitigate challenges and ways to reach international collaboration. After a total of 3 h, the chairs closed the discussion, thanking all of the participants for their constructive participation. As the final semester assignment, the students were required to compose a position-paper advising the government of the country they represented about the expected new reality.

4.3. Allowing time for collaboration

     It is generally recommended to allow time for the parties involved to collaborate with each other, particularly if they're supposed to present a united front in the game. To that purpose, as noted, we allowed the players time before the game to think about their strategies and arguments, and also provided a recess period during which the players talked with each other informally and agreed on strategies and alliances for the rest of the game.

     Naturally, a simulation game, such as the one presented here, has limitations. In this case, limitations are primarily outcomes of the characteristics and requirements of the program under which this class took place. First, since this was a graduate class, it had fewer than 20 students. Thus, a large number of countries could not be included. For this reason, we decided not to include non-state organizations, which in real life may affect the future of space-mining. Second, it was not possible to conduct a long simulation. Third, the students were not space professionals, and therefore lacked technical and other relevant knowledge. Nevertheless, it turned out that this limitation was potentially an advantage, because students were very open-minded about the issues.

     Fourth, it must be noted that students from one country and culture are limited by necessity in their ability to emulate the mindset of people from other nations and cultures. While this limitation is difficult to mitigate completely, the students were asked to prepare for the simulation by reading about the nations they were representing, including details about their populations, cultures, and religious beliefs.

---

5. Simulation outcomes (third part)

     The discussion that ensued during the simulation can be divided into three main sections. First, the discussion concentrated on the possible consequences of the ability to transport materials mined from space to Earth on the stability of the international system and the world order. In this context, the right to exploit commonly held resources, ownership issues, share of profits and knowledge, were discussed. Second was a discussion of the potential opportunities for economic growth, development, and prosperity. In this context, ideas were also raised regarding the potential solutions for the distribution of technological development and the actual distribution of goods. A way was sought to enable a wide range of countries to benefit from the new reality, even if they do not directly engage in space mining, for example, by processing the imported space minerals on Earth.

     Third, a brainstorming session was held regarding the various mechanisms which could and should be developed at the global level. Such mechanisms will be necessary to mitigate the challenges, maximize the opportunities, and reach a broad international consensus among participant states regarding the conduct of world politics in the new international reality.

     The resulting discussion highlighted the tensions between powerful countries and less powerful or weaker countries in the context of the global struggle for resources and power. In general, the participants divided into three main groups of countries. The first group contained spacefaring countries, which have substantial space capabilities and are therefore capable of actively participating in mining minerals in space and transporting them to Earth. For the most part, this group contains the leading world powers. In the simulation, it became clear that the countries in this group compete with each other for leadership of the process of space mining, and the tangible goods and intangible benefits involved, such as the considerable political power accrued. Countries such as the US advocated for an approach that would not restrict development, and instead would encourage innovation and entrepreneurship, while searching for ways to facilitate proper solutions to reach international cooperation. For this reason, during the debate and in response to objections and criticism by other less developed countries, representatives of the leading spacefaring countries highlighted the fact that the new technological breakthroughs would be enjoyed by everyone. They would provide opportunities for all nations to improve their economies, and increase the well-being of their citizens. These statements were aimed at easing the antagonism of the less developed countries, and raising their solidarity and support, in order to achieve a most favorable world-wide political and psychological impact.

     Emerging spacefaring countries composed the second group. Under the leadership of the leading spacefaring nations, these countries were looking for ways to maximize their gains from the new reality. Representatives of these countries focused their efforts on maximizing their chances of taking an active part in the overall process, and upgrading their position in the evolving economy of space mining. The strategic approach they adopted was to find ways to integrate their country into the value chain of space mining, whether in outer space or on Earth as soon as possible and to the maximum extent, in a way that would assure long-term commitment of the leading countries. For example, they bargained with the leading spacefaring nations concerning the establishment of some of the infrastructure on their territories, and negotiated to be part of the future technological development through international collaborations.

     The third group consists of countries with no meaningful space capabilities. Many of the representatives of these countries argued against space mining and the transport of materials to Earth. For them, the new technological and economic reality is a distant and unreachable dream, which imposes serious threats for their economies and stability. In general, their approach represents a historic colonial tension. Their approach can be defined as a serious lack of confidence in the global diffusion of wealth. Many of them argued that the technological and economic development at stake widens the existing gap between them and the developed and advanced countries. They expressed deep concerns that the new reality would work against them, because it would perpetuate current economic and political gaps. Moreover, it would deprive them of their fair and proper participation in the global share of resources, and thus seriously damage their future chances of development. Some of them even demanded that space mining be banned. On a more practical level, they called for a much more inclusive process regarding space mining. In addition, the representatives of these countries called on the international community to develop mechanisms for compensation, which would be provided to them by the countries directly benefiting from space mining. This way, it was argued, they too would be able to enjoy and benefit from the new economic order, and the concept of the “benefit to all mankind” would have practical fulfillment.

     In addition, tensions were also reflected within each of the aforementioned groups. These tensions originated from differing national interests, various approaches to the management of innovation and the aspirations of individual countries in the international system. For example, in the group of spacefaring countries, there was disagreement between the U.S. and other countries, including some of its allies, which often took different positions regarding this issue. Russia and China expressed a more favorable approach to the developing countries, by calling for the development of global mechanisms of compensation.

     In the open discussion conducted in the third part of the simulation, a number of ideas about the proper ways to manage the new situation internationally were raised. Among them was the development of international mechanisms for regulation, licensing, and taxation of space mining, similar to other such international mechanisms, which were adopted in order to organize, regulate and control activities by nations in the global commons, such as the International Seabed Authority. In this capacity, the students suggested the establishment of a “world space bank”, which would be entrusted with the financial management of the revenues from the licensing and taxation. The money thus collected would be used to achieve the following global objectives:

1. Financial compensation for the countries whose economies would be directly and significantly affected by the new economic order. These countries are generally the ones wherein the economies are based on minerals and natural resources, the value of which would significantly drop.
2. Develop technological knowhow and expertise, as well as build up infrastructures, in countries lacking the national capacity to develop indigenous space expertise with their own resources. For example, the Space Bank would conduct training for students and professionals from developing countries, in order to enable these countries to develop initial national capacity in space technology. Another possible direction would be for the Bank to sponsor the establishment of space centers in these countries.
3. Support the establishment of needed infrastructure in developing countries, so as to take part in the value-chain of space mining, especially on Earth.

     Provide funding for global activities to assure safe and sustainable use of space by all countries. For example, funding would be provided to a designated UN agency which would be responsible for monitoring and regulating space traffic, tracking space debris, and conducting active removal of such objects. This innovative idea of establishing a “world space bank” testifies to the creativity which is needed by all players in this “global game” i.e. spacefaring nations, emerging spacefaring nations and players with no significant capabilities. In order to avoid potential conflicts over this expected disruptive capability the challenge leading and emerging spacefaring nations are facing is to find ways to make as many nations as possible parties to the value chain of space mining. The challenge of weaker states is to persuade spacefaring nations to incorporate them into this chain. In addition, the adoption of such mechanisms would demands adaptation by the international legal framework.

5.1. Lessons about space mining

     The lessons of this simulation indicate several issues. First, the game highlighted different group behavior in world politics concerning the new reality, with a sharp distinction between the haves and have-nots. Second, it provides insight regarding different approaches to innovation on the national level and international level. Unsurprisingly, in general, the stronger countries operated according to the principles of “first come, first served”, while others held to the approach of “space for humanity”. Nevertheless, the strong players expressed a pragmatic approach, in which they expressed an understanding of the overall concerns and needs of the international community. They suggested ways to utilize the new reality for the development of mechanisms which would provide service to the overall space environment.

     The concerns raised by the representatives from the developing countries which lack minimal space expertise, regarding the expanded gaps between them and the leading spacefaring nations, are perfectly understandable. Nevertheless, is the strong opposition they expressed to the overall new reality indeed the strategy they should adopt? Would a compensation mechanism work in their favor and serve their long-term goals optimally? What does that tell us about international approaches to innovation and entrepreneurialism? We conclude that under the guise of a demand for a fair distribution of goods, the approach reflected by these countries in the simulation focuses on imposing restrictions on countries rather than on actually developing opportunities to get involved in the process. The focus on mechanisms of compensations rather than on mechanisms to develop capabilities may evolve to be a “self-fulfilling prophecy”, which will preserve and expand existing gaps. Further research is needed to examine the potential effect of compensation methods on the economy and innovation systems in these countries. In the long-run it may turn out that such methods do not optimally serve these countries, rather they will perpetuate their lack of development and lower status.

     An important concern raised by the US representatives was that restrictions on technological development could lead to stagnation and damage the spirit of innovation that pushes the market in general. Indeed, compensation mechanisms by themselves do not produce incentives and opportunities for development. In the long term, compensation mechanisms which are not followed by mechanisms for actual development of skills and knowledge perpetuate and exacerbate the gaps. Instead of resisting development and demanding compensation, these countries should act to achieve full partnership in space mining ventures, which would also contribute to their development.

     On the legal issue, motivation to further develop mechanisms and regulations for this new reality stems from the fact that most items included in the existing space treaties were established when human activity in space was dominated by governmental activity. Therefore, these treaties reflect the perspectives and needs of states. Nowadays, the development of private and commercial enterprises in space requires new perspectives and thinking regarding regulation.

     Finally, looking ahead to the time when space mining will become a reality, and given its positive potential and negative challenges, we advise that this issue be discussed in international forums sooner than later. Scholars and professionals should put their minds to the variety of technological, scientific, legal, political and economic issues that are expected to arise. By doing so ahead of time, they will be able to develop principles and frameworks that can maximize the benefits of the new reality while minimizing the risks to global stability.

5.2. Lessons for future simulations

     Overall, the simulation proved to be a success – both in pedagogically and in the way it encouraged thinking about a disruptive technological subject, identifying some of its complex consequences on the world, and devising ways to deal with them.

     When asked for insights about the simulation, the students' responses were overwhelmingly positive. Indeed, several students requested that such simulations be held throughout the semester, starting with an introductory session in which the students introduce their nations to each other.

     One of the students expressed his opinion in the following manner, which highlights the usefulness of the simulation as a way to analyze issues international relations:

“I actually understood how international relations are really made, who 'my friends' are, who's against me and who stands with me …. ”

     One of the main lessons derived from the simulation concerned the necessity of having breaks between the three discussion sessions. Breaks, even short ones of only a few minutes, enabled the participants to talk with each other privately, frequently reaching understandings and agreements ‘behind the scenes’. Coalitions and collaborations arose mainly as a result of such breaks in the discussions.

     We strongly believe that simulations and role playing games could be used to analyze and better understand other international situations as well, and look forward to conducting similar simulations in the future.

6. Conclusions

     In this study, we examined the potential impact that could result from a successful space mining venture, and the initial responses by nations around the world. We found that while spacefaring nations were largely eager to exploit resources from space, most developing nations in the simulation were far less excited about the possibility, and understandably feared that this technological breakthrough would disrupt their own growth and development by making their natural resources virtually worthless overnight.

     We believe that successful ventures in the field of space mining would have to address these international issues and tensions sooner or later. One potential solution that arose from the simulation was creating a mechanism of a Space Bank that would tax successful space mining ventures, and use the money to help promote space-related science and technology in developing nations. This Space Bank would thus serve as a ‘ladder to space’ that would support the advancement of all nations in their outreach towards outer space.

     The methodology underlying the simulation has proven to be particularly useful, both for teaching about this complex topic, and for promoting brainstorming and out-of-the-box thinking. We believe that similar simulations could be used to analyze the consequences of many other disruptive developments. Other simulations could be used, for example, to analyze the possibility of using the mined resources to sustain a “deep space economy”, or to examine the security risks posed by asteroids dragged into orbits around Earth. Finally, larger simulations in the future should include non-state actors, such as commercial firms, terrorist groups and representatives of the scientific community.

(ed note: see report for references)

• 

      "So what,” a rather harsh voice declared. “I'm T. Semyon Braunstein, Administrator of NAUGA-State, and we want to talk to you about our gold which you have been dispensing in a very cavalier fashion."
     "You want it back, I take it?"
     "Damn straight! We know you made a big haul when you took over NAU-Ceres I and we do indeed want it back."
     "Well, now,” Cantrell said, “how much of your treasure am I supposed to have plundered?"
     "We frankly don't know,” Braunstein replied, “and the presumption is that all the gold you have is ours in absence of proof to the contrary."
     "That would appear to be arguable,” said Cantrell. “Let's stick to the facts."
     "How much did you take?” Braunstein asked.
     "One million four hundred and eighty thousand ounces. That's what, five tons? The entire lot was minted into Ceres d'Or and put into local circulation."
     "You issued gold-backed paper, too,” McQuayle said, “a lot more than any one and a half million ounces, by damn!"
     "So what? Gold-backed paper is paper, not gold."
     "We want the gold that's backing it up,” Braunstein said. “That's our gold, you pirate!"

     "Don't be such a (expletive deleted) fool,” Cantrell snapped. “Ceres—all the mines on Ceres—never produced more than about twelve million ounces a year. That's what—maybe forty tons. Today, here at Castillo Morales, I am depositing five thousand six hundred and sixty tons of gold. How did I get my hands on one hundred and forty-one years’ worth of your peak production, hey? Answer me that, clown!"
     There was a rather long pause as McQuayle and Braunstein digested the information. “Where did the gold come from, then?” Braunstein asked.

     "We used the big laser to refine a cubic kilometer of nickel-iron. It took us nearly a year."
     "How much gold was there?” asked McQuayle.
     "The nickel-iron assayed 0.75 ppm gold by weight,” replied Cantrell. “What's the weight of a cubic kilometer of nickel-iron, 8×10⁹ tons?"
     "And you could run off another five or six thousand tons of gold next year?” Braunstein asked.
     "And the year after,” Cantrell agreed. “And the (Japanese) won't bother me about it because they have big lasers on most of their space stations, and most of the space stations with big lasers are close to large masses of nickel-iron. I've given them the whole technology."

     "The gold standard,” McQuayle said weakly, “you've just shot the gold standard in the ass—one location producing five thousand tons of gold a year! Fifty (asteroid colonies) would produce—what? Two hundred fifty thousand tons? And more would be coming on stream all the time … we pegged the dollar at eight hundred fifty to the ounce … we can't hold it there … we can't limit production—my God! What's our money going to be worth?"
     "I suggest you get a handle on the paper,” Cantrell said, “because if you stick with the gold standard, you're in for one hell of an inflation."
     "The gold mines on Ceres seem to be a bit redundant,” Braunstein remarked at last. “Do the Japanese realize that the gold you're dumping on them isn't worth (expletive deleted)?"
     "No. They think, like you did, that it was stolen from the NAU.” Cantrell paused for a moment to watch the forklift trucks moving the pallets of gold bars. “Premier Ito will be announcing our agreement in about ten minutes, at 1900. I told him we'd work out the details when I got back to Rosinante."

     "Well, goddamnit, get my financial advisors!” Braunstein yelled.
     "I beg your pardon?"
     "I wasn't talking to you, Cantrell."
     "You've totally destroyed the economy of the world,” McQuayle said. “What did you get out of it, Cantrell?"
     "Survival. The Japanese Fleet is already heading away from Rosinante. Besides, I expect the economy of the world will survive."

• 

(ed note: Antonio has developed a magnetic array system that allows scanning circumstellar disks to detect asteroids with valuable deposits of rare metals. He has hired a ship to go scan an unexplored circumstellar disk and bring back a few megatons of gold)

      “Thank you, Captain. My colleagues and I want to fly the Lady Macbeth on a prospecting mission.”
     “For planets?” Roman asked curiously.
     “No. Sadly, the discovery of a terracompatible planet does not guarantee wealth. Settlement rights will not bring more than a couple of million fuseodollars (the empires are not on the gold standard, instead they are on the Helium-3 standard), and even that is dependant on a favourable biospectrum assessment, which would take many years. We have something more immediate in mind. You have just come from the Dorados?"
     “That’s right," Marcus said. The system had been discovered six years earlier, comprising a red dwarf sun surrounded by a vast disc of rocky particles. Several of the larger chunks had turned out to be nearly pure metal. Dorados was an obvious name; whoever managed to develop them would gain a colossal economic resource. So much so that the governments of Omuta and Carissa had gone to war over who had that development right.
     It was the Garissan survivors who had ultimately been awarded settlement by the Confederation Assembly. There weren't many of them. Omuta had deployed twelve antimatter planetbusters against their homeworld.

---

     “While we're waiting," Katherine said. “I have a question for you, Antonio.”
     She ignored the warning glare Marcus directed at her.
     Antonio’s bogus smile blinked on. “If it is one I can answer, then I will do so gladly, dear lady.”
     “Gold is expensive because of its rarity value, right? "
     “Of course."
     “So here we are, about to fill Lady Mac’s cargo holds with 5,000 tonnes of the stuff. On top of that you’ve developed a method which means people can scoop up millions of tonnes any time they want. If we try and sell it to a dealer or a bank, how long do you think we’re going to be billionaires for, a fortnight?”

     Antonio laughed. “Gold has never been that rare. Its value is completely artificial. The Edenists have the largest stockpile. We don't know exactly how much they possess because the Jovian Bank will not declare the exact figure. But they dominate the commodity market, and sustain the price by controlling how much is released. We shall simply play the same game. Our gold will have to be sold discreetly, in small batches, in different star systems, and over the course of several years. And knowledge of the magnetic array system should be kept to ourselves.”
     “Nice try, Katherine," Roman chuckled. “You'll just have to settle for an income of a hundred million a year."

• 

Secondly, and more subtly, the right elements have to be accessible on the planet for it to be colonizable. This seems a bit puzzling at first, but what if Centauri Bb is the only planet in the Centauri system, and it has only trace elements of Nitrogen in its composition? It's not going to matter how abundant everything else is. A planet like this—a star system like this—cannot support a colony of earthly life forms. Nitrogen is a critical component of biological life, at least our flavour of it.

In an article entitled "The Age of Substitutibility", published in Science in 1978, H.E. Goeller and A.M. Weinberg proposed an artificial mineral they called Demandite. It comes in two forms. A molecule of industrial demandite would contain all the elements necessary for industrial manufacturing and construction, in the proportions that you'd get if you took, say, an average city and ground it up into a fine pulp. There're about 20 elements in industrial demandite including carbon, iron, sodium, chlorine etc.

Biological demandite, on the other hand, is made up almost entirely of just six elements: hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur. (If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It's called cellulose.)

(ed note: actually, that turns out not to be the case. Cellulose does not contain nitrogen or phosphorus, both of which are vital. )

• 

“Demandite” is the word used by mineral economists to describe the materials that must be provided— usually by mining— to meet the needs of civilization. In the usual terrestrial setting, air and water are assumed to be freely available, and fossil fuel (natural gas, crude oil, and coal) is considered a necessity. In space, where dependence on solar energy is the norm, and where air and water must be “mined”, the numbers are different. The proportions of mineral needs, however, are otherwise generally similar. You can then ask how much of each material (iron, carbon, nitrogen, aluminum, copper, oxygen, water, nitrogen, etc.) is needed to be in circulation to support one person, depending on “renewable” (inexhaustible) solar energy to drive industry, agriculture, and recycling. We can then compare those requirements to the natural resources available on bodies in nearby space, and calculate how many people could be supported at each of those locations.

The proportions of these necessary materials (the relative abundances of water and iron, for example) are very different on the Moon, Mars, and nearby asteroids. The Moon, for example, is severely deficient in all volatile elements, including carbon, nitrogen, hydrogen, and chlorine, Mars, with its tenuous atmosphere and widespread ice deposits, fares better. But best by far is the match between the composition of near-Earth asteroids (NEAs) and “space-based demandite”. The 1000 or so kilometer-sized near-Earth asteroids contain enough of every essential element to support a population of 10 billion people from now until the Sun dies of old age. The NEAs, however, are a renewable resource: in nature, the rate at which NEAs are lost by collision with planets and ejection from the Solar System is compensated by recruitment of fresh asteroids kicked into near-Earth space by Jupiter’s gravitational interactions.

But what about the main Asteroid Belt? The answer is startling: the Belt contains one million times as much mass as the entire NEA population. Again depending on the Sun for power, the Belt could support a population of 10 million billion people— a million times the ultimate carrying capacity of Earth. With that many people, wouldn’t we be running out of solar power? Not really— even under these extreme assumptions, we would require less than one millionth of the Sun’s output energy.

The non-renewable resources available to Earth-bound humanity are finite. The resources available to a space-faring humanity are effectively infinite.

The ultimate objective of space industrialization is to create a growing economy in space which can eventually become self-sufficient. Space industry is presently supported by sales of goods with extremely high intrinsic values, such as satellites for communications, research, navigation and reconnaissance. Low-volume production of exotic goods in the zero-gravity and weightless conditions afforded in near-Earth space may broaden the market for space produced goods. However, in all these cases the cost of transporting the goods or raw materials into low-Earth orbit will add $200-$700/kg to the product price for a period of 15 years and thus place a sharp limit on the ultimate terrestrial market (ref. 1). There appears to be a way of circumventing the present high cost of launching materials from the Earth into space. This can be done by acquiring bulk raw materials from the Moon or asteroids and processing them in space into economically valuable products. Initial bulk material costs could be of the order of $25/kg in high-Earth orbit (see Salkeld appendix)and the cost would drop with experience. There would be two effects of lower material costs. First, the space economy could begin approaching the richness and cost structures of our present terrestrial economy. Secondly, the range of space products that could be sold for terrestrially-related use either in space or on Earth would be greatly expanded.

The Moon can supply most of the mass needed for large-scale industry in space. There are two ways to approach the proof of this statement. The first is to look in detail at the materials needed to construct specific products in space. At this point in time the production of space solar power stations is an attractive candidate because of the high value per unit mass of such objects and because of the large number of stations which could be required (>200 in next 30 years). Analyses even of designs not optimized for lunar elements reveal that at least 60 percent of the required silicon, aluminum and oxygen could be obtained from the Moon and the total mass lifted from Earth could be reduced about 80 percent by utilizing lunar materials.

Alternatively, one can compare the nonfuel distribution of nonrecoverable elements (weight fraction) utilized in the industrial economy of the United States with elements present in the lunar soil as is shown in table 1. The fraction of these elements which can be extracted with reasonable and presently available chemical processing techniques from beneficiated lunar ores is the subject of two companion papers (by Williams et al. and Rao et al.respectively) discuss extraction of Si, O, Fe, Al, Ti, and H₂O. Using these and other proposed extraction procedures most of the components of the synthetic molecule of "Demandite", which constitute most of the nonfuel material inputs to American industry, could be provided in deep space at less cost per unit mass than the launch cost of the complete suite of the constituent elements directly from Earth in large tonnages until the mid-1990's.

• 

TABLE 1 .- NONFUEL DEMANDITE (U.S., 1958) COMPARED TO ELEMENTARY DISTRIBUTIONS OF SOIL AT THE APOLLO-15 LANDING SITE (WEIGHT FRACTIONS)

	Nonfuel demanditea	Apollo 15 mare-low Ti	Enhancement required	Bulk soil (1 unit)b
Si	0.2444	0.2158	1.13	--	0.0286
O	.4547	.4130	1.10	--	.0417
Fe	.0479	.1535	.31	0.1056	--
Al	.0023	.0546	.04	.0523	--
Mg	.0017	.0681	.025	.0664	--
(Cu, Zn, Pb)	.0020	2.2 (-5)c	90	--	.0020
Xd	.0030 Σ -.0569	0.0189 Σ -.2951	.15	.0159	--
Cae	.1417	.0696	2.0	--	.0721
Na	.0095	.0023	4.1	--	.0072
S	.0058	.0006	9.7	--	.0052
Ke	.0021	.0008	2.6	--	.0013
Pe	.0019	.0005	3.8	--	.0014
Cl	.0147	7.6(-6)	1934	--	.0147
Ne	.0083	8(-5)	103	--	.0083
Ce,f	.0574	9.5(-5)	604	--	.0573
Hf	.0025	6.4(-5)	350	--	.0025
Otherg	.0001	.0023	.03	.0022	--
	1.000	1.000	--	(+)0.2424	(-)0.2423

^bFormula = (Wt. fraction lunar element)- (Wt. fraction demandite).
^c(N) ≡ 10^N
dx - Mn, Ti, Cr, Ba, F, Ni, Ar, Sri, Br, Zr.
^eImportant agriculturally.
^fConcentrated in the smaller grains (<50μ)
^gVirtually the complete suite of elements is present in these areas,
but their contributions (on the ppm and ppb levels) are lost in
the errors of the sum over the listed elements. Trace element concentrations may vary greatly from one site to another.

---

Notice in column 4 of table 1, that the major demandite components (Si, O, Fe, Al, Mg, X, Ca, Na, K, P, and S) are present either in adequate concentrations or in enrichments that are 10 times the specific fractions of the soil. Beneficiation of soil components to enhance and possibly simplify. known chemical extraction processes should be achievable using electrostatic, magnetic, dielectric and mechanical techniques and careful site selection. Elements such as Cu, Zn, Pb, H, Cl, N, C, and other trace elements comprise 8.4 percent of the demandite molecule. These elements would be shipped from Earth, eventually located from other sources, such as non-Apollo sites, or other materials substituted for them. In any event, it is clear that of order of 90 percent of the present day inventory of industrial elements can be provided from known lunar soils. Lunar soil processed to provide 90 percent of the demandite complement at $20/kg (i.e., Si, Al, Fe, Mg, Ca, and O) and the remainder supplied from Earth at $300/kg would provide the in-space demandite molecule at a cost of about $50/kg or 17 percent of the direct supply cost.

It is very clear, however, that substitution of materials, which is being required in the terrestrial economy even now, will permit much greater use of lunar materials both in general and for specific products. Thus, the cost of space "demandite" should approach the cost of the lunar processed materials.

The economic value to Earth of the Moon or the asteroids as a source of raw materials is strongly dependent on the total retrieval and elemental separation costs of the raw materials. Figure 1 is a qualitative description of the costs of goods or end-use-material on a dollar per kilogram basis (horizontal axis) versus the differential output of the total value of goods in the U.S. economy in billions of dollars per dollar per kilogram or (Δ10⁹ $/($/kg)) for a total GNP of $10¹².

Most goods now sell for less than $10/kg with most between $0.1/kg and $2/kg. Transport into low-Earth orbit (LEO) from the Earth presently adds more than $500/kg and thus confines goods produced in space to a tiny fraction of the potential terrestrial market (right of arrow 1 in Figure 1). Solar power stations are estimated to be economically feasible at $140/kg . Supplying the bulk of the required construction material from the Moon at $20/kg (arrow 2 in Figure 1) would clearly improve the economics and decrease the cost of the power supplied to Earth. If sources of industrial feedstock can be developed in deep space with costs of less than $0.5/kg (arrow 3 in Figure 1) then many of the Earth-produced goods can be considered for potential space manufacture. It is conceivable that industrial material can be supplied at such low costs from the Moon or asteroids assuming normal industrial "learning curve" experience occurs.

• 

Many people assume that the Moon is the "logical next step" in space development; it is, after all, the closest source of raw materials in space. But why go to the Moon for resources?

Access to Asteroids

The Moon's proximity offers obvious advantages: short travel times make human crews safer and cheaper, and brief light-lag eases control of remote operation. If, however, initial "mining" operation will simply fill bags with loose material, then virtually unsupervised devices—sweeper robots—seem practical; neither travel time nor light-lag then matter much, and the advantages of proximity fade. As space industry grows, human beings will have the run of the Solar System; even earlier, semi-autonomous robots could likely handle more than mere dirt-sweeping. Meanwhile, complex processes can be confined to near-Earth space.

The relative motions of Earth and any given asteroid make good transfer opportunities relatively infrequent, and infrequent transfers would increase the inventory cost of resources stockpiled for use between deliveries. The main cost tied up in this inventory, however, would be that invested in its transportation. Low delta v's, aerobraking, and use of efficient, low-thrust propulsion systems promise to make the transportation cost of asteroidal materials far less than that of lunar materials; this seems likely to swamp the effect of inventory costs.

Still, a systems analysis would be needed to quantify the costs of infrequent launch windows. For example, how greatly will scheduling inefficiencies decrease the useful operating time of propulsion systems? How rapidly do such costs lessen as the number of surveyed target asteroids grows? Such factors can only be estimated now, but the overall prospects look good. With many target asteroids, more windows will open and such costs will lessen; a modest search should find many as accessible as the best now known. Further propulsion systems (such as Lightsails) could make many known asteroids easy to reach. Asteroids seem more accessible than the Moon, despite their greater distances.

Orbiting Ores

The sheer size of the Moon increases the possibilities for ore formation, at least compared to those in a smaller version of itself. Separation on a vast scale, however, matters less than the degree of concentration. If some process swept up all the uranium in a typical cubic kilometer of the Earth's crust (the volume of a small asteroid), the resulting block of uranium would mass over 10,000 tons. If, however, all the uranium in Earth's crust were concentrated a hundredfold, a block more massive than any asteroid would result, but it would hold a mere 400 parts per million. Greater concentration would be worth more than greater quantity, particularly to a small-scale industry. Uranium itself, of course, seems worth little in free space, given the steady flood of sunlight.

Separation processes have concentrated materials in both the Moon and asteroids. Geochemists classify elements as siderophile (chiefly found in the iron phase), chalcophile (chiefly found in the sulfide phase), lithophile (chiefly found in the rock phase), and volatile (chiefly found—or lost—in the vapor phase).

The Moon is enriched in refractory lithophile elements, but at the expense of depletion in siderophile, chalcophile, and (especially) volatile elements.

The asteroids, in contrast, vary: rocky asteroids are enriched in lithophile elements; nickel-iron asteroids are enriched in siderophile elements (and often hold nuggets of sulfide); carbonaceous chondrite asteroids, while not enriched in volatiles (compared to the Sun or Jupiter), nevertheless contain abundant water and hydrocarbons. Some asteroids, such as the chondrites common near Earth, hold a separable mixture—grains of metal and sulfide in a rocky matrix containing traces of water and carbon. The Moon's separation discarded too much.

The refractory lithophiles include aluminum, titanium, and magnesium; these may seem attractive for space use, since they are "aerospace metals." Asteroidal (that is, meteoritic) samples hold up to 27% aluminum oxide, and some carbonaceous chrondrites contain veins of water—soluble magnesium salts—the Moon has no monopoly on such metals.

Surprisingly, however, space industry has little special need for light metals. "Aerospace" today suggests vehicles, devices flung about repeatedly (or thrown very high) by burning fuels; low mass is important to their performance. Space industrial facilities— factories, stations, power plants—will be different: in use, they will simply orbit, as would a feather or boulder. Added mass can even help, by blocking radiation and slowing orbital decay.

Simple delivered cost seems most important, and this will include the costs of both transportation and refining. Energy requirements can indicate relative costs. Call the energy needed to lift a kilogram from the Moon one unit. Returning a kilogram from a target asteroid will require less than one unit; melting and refining a kilogram of asteroidal steel will require about a half a unit. The energy needed to break a kilogram of light metals free from lunar oxides, however, is roughly ten units. Further, asteroidal steel can be melted and refined using inexpensive heat from a solar furnace, while planned processes for reducing lunar oxides require expensive electric power. Process complexity issues likewise seem to favor steel.

For low-cost space construction, asteroidal steel seems best; a low-expansion nickel-iron alloy (Invar) could be used to avoid thermal distortion. Where low mass matters, graphite and plastics are becoming popular, and asteroidal hydrocarbons provide a feedstock unmatched on the Moon. For market value on Earth, precious and strategic metals from asteroids seem attractive. I know of no lunar materials superior to terrestrial ores. (The suggestion that lunar titanium might find a terrestrial market was incorrectly attributed to me in The High Frontier, O'Neill apparently confused me with another researcher.) Asteroids, however, hold siderophile metals like those that sank to Earth's core— separated, yet not beyond reach.

Speculative Prospects

Stephen Gillett discusses the possibility of lunar ores enriched in incompatible elements (those not easily incorporated in crystals of common minerals as magma cools and solidifies). He notes that water is commonly considered vital to concentrating incompatible elements in the residual liquid as magma solidifies, but proposes that traces of chlorine and sulfur might have played a similar role to that of water in the dry lunar magmas; KREEP (a rock widely distributed on the Moon, which is highly enriched in incompatible elements potassium [K], Rare Earth Elements and Phosphorus [P]) shows that some concentration occurs. The experiments he suggests seem well worth doing, to see if ores containing "chlorine, lithium, beryllium, zirconium, uranium, thorium, the rare-earth elements, and so forth" might indeed have formed. These elements are not critical to early space development, however, and chlorine—perhaps the most valuable, given its many uses in industrial chemistry—makes up 0.8% of the soluble salts found in carbonaceous chondrites.

One can equally well speculate regarding possible asteroidal ores not yet seen in terrestrial samples, of course. The Moon has been sampled in relatively few sites; likewise, most meteoritic samples are thought to come from relatively few parent bodies. Some classes of meteorite are represented by but one specimen, suggesting that some—represented by none—remain unknown. Nickel-iron meteorites contain a spectrum of nickel content ranging up to 34%—except for one that contains 62%. Our lunar samples contain grains thrown from far across the lunar surface; do they contain comparable evidence for unusual concentrations of valuable materials?

The asteroids, though smaller and faster-cooling, seem a match for the Moon as targets for speculative prospecting. Vesta, for example, appears basaltic and differentiated (like the Moon) and has over one-tenth the Moon's diameter. Many meteorites were melted and resolidified; asteroidal materials contained water, which perhaps mobilized incompatible elements. Further, comparing rock to rock, metal to metal, and sulfide to sulfide, concentrations of trace elements have been found to vary from sample to sample by factors of several hundred or more.

Hydrothermal processes (surely lacking on the Moon!) form many terrestrial ores; they require porous rock saturated with water, together with heating to drive convection, dissolve compounds in a large volume, and deposit them in a smaller volume. Some carbonaceous chondrites show veins of water-soluble salts; other signs point to their having been water-saturated for at least a thousand years. The cores of some asteroids melted, showing the presence of ample heat. Thus, hydrothermal deposits are not inconceivable. Similarly, deposits formed by volatilization and subsequent condensation in vents seem possible; metals such as tin and lead might be concentrated by such a mechanism. Finally, the composition of asteroidal rocks before and after their melting and differentiation strongly suggests that a sulfide phase, troilite, may be found in massive veins. One troilite-rich meteorite is known; any pure troilite meteoroids are thought to be destroyed by atmospheric entry (as are those carbonaceous chondrites richest in water and organics). In short, the asteroids' known resources seem better than the Moon's, and their unknown resources seem more promising.

An Asteroid Scenario

To make the idea of asteroid mining more vivid, a scenario may help. How might the process begin, and where could it lead?

First, we drop our eyes from the splendor of the full Moon, shake our heads to clear them, and look seriously at the choice of asteroidal resources vs. lunar resources. In part for scientific reasons, we support asteroid missions and the Spacewatch asteroid-search telescope. Recognizing the high thrust-to-weight ratio of metal films in sunlight (and their lack of fuel consumption), we better define Lightsail construction procedures and configurations. Agreement grows that asteroids have valuable, accessible resources. Space industry draws investment. Probes survey newly found asteroids to select the best targets for initial use. Government and industry decide that a fraction of the price of the Shuttle is little to pay to open the Solar System; Lightsail development begins in earnest.

Lightsail production begins in orbit, and sails depart for nearby asteroids. They deliver devices that sweep loose regolith into bags, then they return the bags to low Earth orbit. Engineers use the mass as radiation shielding for habitable modules of space stations, and for hardening military satellites. The Russians protest dirt in orbit as "an anti-satellite weapon." Water from carbonaceous chondrites is electrolyzed, producing cheap fuel in orbit for hydrogen/oxygen rockets; radiation shielding and fast, inexpensive rockets lead to a construction base in geosynchronous orbit.

Total sail capacity grows steadily as orbital factories continue production. Selected asteroidal steels are purified, removing over $1,000 of platinum metals per ton, then foamed in zero gravity for sale on Earth. Steel structures become common in orbit. The orbital industrial complex expands. Mass production of sails lowers the transport cost from certain asteroids to less than $l/kg; use of asteroidal nickel in sail reflectors further lowers the cost to $0.10/kg. Nickel and cobalt, then steel, follow platinum to markets on Earth. Steam turbine power satellites with steel radiators become economical. Space industry rivals genetic engineering and electronics as a growth sector in the Western economy.

An expedition at last departs to build industrial facilities at the two most accessible asteroids, to pre-process metals and organic materials for shipment and easy capture through atmospheric braking. With cheap steel and water, space stations become large enough to hold parks and gardens, then grow still larger. People stay longer. They bring their families.

With cheap fuel, the cost of reaching the lunar surface drops dramatically. A Moon base is built using asteroidal steel and propellants; for scientific and sentimental reasons advocates of Moon mining have an uphill battle against the conventional wisdom about space development. In time, however, the Moon becomes a source of aluminum and titanium for use in space industry, since it proves to be richer in these materials than are the more accessible asteroids.

This scenario assumes use of Lightsails; asteroidal resources would remain attractive even using ion engines, deployable solar sails, or chemical rockets burning liquid oxygen and hydrogen (LOX) and liquid hydrogen (LH2) from electrolyzed asteroidal water.

Twenty-eight years ago, in a fit of political hysteria, the U.S. took a path that bypassed building a shuttle and space station, building instead a giant missile to fulfill an ancient dream. In 1969 it reached its goal, but at a great price to true space development: the "Moon shots" dominated the news about space, and made spaceflight seem like an expensive stunt. The space program collapsed afterwards.

Today, it is said that a lunar base is the logical next step. There is even talk of lunar colonies, far from the terrestrial markets that could pay for them. Let us turn our eyes from the "romance" of the Moon—long enough, at least, to consider sailing on sunlight to mine steel, water, gold, and platinum from flying mountains.

(ed note: The Supersonic Dust Roaster heats lunar or asteroidal regolith until it is molten and extracts the oxygen. It will operate in both low-gravity (on asteroid) and microgravity (in orbit) conditions.)

Regolith (pulverized minerals) is heated resistively in a crucible until it melts and becomes conductive. Inductive heating raises the temperature to 3000°K, at which point the vapor pressure over the melt reaches approximately 100 kPa, and includes a large fraction of molecular and atomic oxygen. A de Laval nozzle fitted to an aperture into the vapor chamber creates a supersonic flow of the vapor. As the superheated vapor passes down a drift tube, it cools to the point where suboxide minerals condense and flocculate into agglomerates.

As these accrete further their supersonic inertia turns them into ballistic particulates, disengaged from the gas flow. Oxygen, which remains a gas until a frosty 90°K, can be culled out of the stream with molecular skimmers and captured into praseodymium cerium oxide adsorbate beds.

This patent pending system works great in calculations, but what material can withstand such temperatures with an atmosphere containing highly-reactive monatomic oxygen?

---

Thorium oxide has the highest temperature of any ceramic, melting at 3300°K. It is already oxidized, and can withstand the energetic monatomic oxygen, making it ideally-suited to the Dust Roaster’s need. However, thorium is mildly radioactive.

---

As a result of this research effort, the team was able to identify three candidate materials for the Dust Roaster. Thorium oxide could not be entirely discounted. The radiation dose received from an astronaut working on the Dust Roaster is far less than that received due to background radiation from the sun and from highly-energetic galactic cosmic rays. Oxides of hafnium or yttrium would be a good second choice, and when properly stabilized, provided a modicum of cooling is included in the Dust Roaster design. As a third choice, a mixed ceramic based on zirconium oxide is readily available, inexpensive, and there is an abundance of experience working with this material. Keeping this material cooled below its softening point will require a thermal management system, a challenge since the thermal conductivity is quite low.

---

For the details, read the patient

• 

• 

• 

• 

Al-O2 rocket
Exhaust velocity	2,648.7 m/s
Thrust	292,600 N
Specific Power	112 kg/MW
Engine Power	500 MW
Frozen Flow eff.	79%
Thermal eff.	98%
Thrust Power	387 MW

Solar Carbothermal Refinery

Although aluminum is common in space, it stubbornly resists refining from its oxide Al₃O₂. It can be reduced by a solar carbothermal process, using carbon as the reducing agent and solar energy. Compared to carbo-chlorination, this process needs no chlorine, which is hard to obtain in space. Furthermore, the use of solar heat instead of electrolysis allows higher efficiency and less power conditioning. The solar energy required is 0.121 GJ/kg Al.

The aluminum and oxygen produced can be used to fuel Al-O₂ chemical boosters, which burn fine sintered aluminum dust in the presence of liquid oxygen (LO₂). Unlike pure solid rockets, hybrid rockets (using a solid fuel and liquid oxidizer) can be throttled and restarted. The combustion of aluminum obtains 3.6 million joules per kilogram. At 77% propulsion efficiency, the thrust is 290 kN with a specific impulse of 285 seconds. The mass ratio for boosting off or onto Luna using an Al-O₂ rocket is 2.3. In other words, over twice as much as much fuel as payload is needed.

Gustafson, White, and Fidler of ORBITECTM, 2010.

---

Carbochlorination Refinery

Metal sulfates may be refined by exposing a mixture of the crushed ore and carbon dust to streams of chlorine gas. Under moderate resistojet heating (1123 K) in titanium chambers (Ti resists attack by Cl), the material is converted to chloride salts such as found in seawater, which can be extracted by electrolysis.

The example shown is the carbochlorination of Al₂Cl₃ to form aluminum. Al is valuable in space for making wires and cables (copper is rare in space). The electrolysis of Al₂Cl₃ does not consume the electrodes nor does it require cryolite. However, due to the low boiling point of Al₂Cl₃, the reaction must proceed under pressure and low temperatures.

Other elements produced by carbochlorination include titanium, potassium, manganese, chromium, sodium, magnesium, silicon and also (with the use of plastic filters) the nuclear fuels ²³⁵U and ²³²Th. Both C and Cl2 must be carefully recycled (the recycling equipment dominates the system mass) and replenished by regolith scavenging.

Dave Dietzler

• 

The Sabatier reaction or Sabatier process was discovered by the French chemist Paul Sabatier in the 1910s. It involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures in the presence of a nickel catalyst to produce methane and water. Optionally, ruthenium on alumina (aluminium oxide) makes a more efficient catalyst. It is described by the following exothermic reaction:

CO₂ + 4 H₂ → CH₄ + 2 H₂O + energy

∆H = −165.0 kJ/mol

(some initial energy/heat is required to start the reaction)

International Space Station life support

Oxygen generators on board the International Space Station produce oxygen from water using electrolysis; the hydrogen produced was previously discarded into space. As astronauts consume oxygen, carbon dioxide is produced, which must then be removed from the air and discarded as well. This approach required copious amounts of water to be regularly transported to the space station for oxygen generation in addition to that used for human consumption, hygiene, and other uses—a luxury that will not be available to future long-duration missions beyond low Earth orbit.

NASA is using the Sabatier reaction to recover water from exhaled carbon dioxide and the hydrogen previously discarded from electrolysis on the International Space Station and possibly for future missions. The other resulting chemical, methane, is released into space. As half of the input hydrogen becomes wasted as methane, additional hydrogen is supplied from Earth to make up the difference. However, this creates a nearly-closed cycle between water, oxygen, and carbon dioxide which only requires a relatively modest amount of imported hydrogen to maintain.

Ignoring other results of respiration, this cycle looks like:

The loop could be further closed if the waste methane was separated into its component parts by pyrolysis:

The released hydrogen would then be recycled back into the Sabatier reactor, leaving an easily removed deposit of pyrolytic graphite. The reactor would be little more than a steel pipe, and could be periodically serviced by an astronaut where the deposit is chiselled out.

Alternatively, the loop could be partially closed (75% of H₂ from CH₄ recovered) by incomplete pyrolysis of the waste methane while keeping the carbon locked up in gaseous form:

The Bosch reaction is also being investigated by NASA for this purpose and is:

CO₂ + 2H₂ → C + 2H₂O

The Bosch reaction would present a completely closed hydrogen and oxygen cycle which only produces atomic carbon as waste. However, difficulties maintaining its temperature of up to 600°C and properly handling carbon deposits mean significantly more research will be required before a Bosch reactor could become a reality. One problem is that the production of elemental carbon tends to foul the catalyst's surface, which is detrimental to the reaction's efficiency.

Manufacturing propellant on Mars

The Sabatier reaction has been proposed as a key step in reducing the cost of manned exploration of Mars (Mars Direct, Interplanetary Transport System) through In-Situ Resource Utilization. Hydrogen is combined with CO₂ from the atmosphere, with methane then stored as fuel and the water side product electrolyzed yielding oxygen to be liquefied and stored as oxidizer and hydrogen to be recycled back into the reactor. The original hydrogen could be transported from Earth or separated from martian sources of water.

A variation of the basic Sabatier methanation reaction may be used via a mixed catalyst bed and a reverse water gas shift in a single reactor to produce methane from the raw materials available on Mars, utilizing water from the Martian subsoil and carbon dioxide in the Martian atmosphere. A 2011 prototype test operation that harvested CO₂ from a simulated Martian atmosphere and reacted it with H₂, produced methane rocket propellant at a rate of 1 kg/day, operating autonomously for 5 consecutive days, maintaining a nearly 100% conversion rate. An optimized system of this design massing 50 kg "is projected to produce 1 kg/day of O₂:CH₄ propellant ... with a methane purity of 98+% while consuming 700 Watts of electrical power." Overall unit conversion rate expected from the optimized system is one tonne of propellant per 17 MWh energy input.

Detailed chemical reactions

(ed note: Note the slight problem with using the Sabatier process to make rocket fuel:)

The stoichiometric ratio of oxidizer and fuel is 2:1, for an oxygen:methane engine.

CH₄ + 2 O₂ → CO₂ + 2 H₂O

However, one pass through the Sabatier reactor produces a ratio of only 1:1.

(ed note: the problem being that the process as is does not generate enough oxygen to burn with all the methane being produced)

More oxygen may be produced by running the water gas shift reaction in reverse, effectively extracting oxygen from the atmosphere by reducing carbon dioxide to carbon monoxide.

Another option is to make more methane than needed and pyrolyze the excess of it into carbon and hydrogen (see above section) where the hydrogen is recycled back into the reactor to produce further methane and water. In an automated system, the carbon deposit may be removed by blasting with hot Martian CO₂, oxidizing the carbon into carbon monoxide, which is vented.

A fourth solution to the stoichiometry problem would be to combine the Sabatier reaction with the reverse water gas-shift reaction in a single reactor as follows:

3 CO₂ + 6 H₂ → CH₄ + 2 CO + 4 H₂O

This reaction is slightly exothermic, and when the water is electrolyzed, an oxygen to methane ratio of 2:1 is obtained.

Regardless of which method of oxygen fixation is utilized, the overall process can be summarized by the following equation:

2 H₂ + 3 CO₂ → CH₄ + 2 O₂ + 2 CO

Looking at molecular masses, we have produced sixteen grams of methane and 64 grams of oxygen using four grams of hydrogen (which would have to be imported from Earth unless Martian water was electrolysed), for a mass gain of 20:1; and the methane and oxygen are in the right stochiometric ratio to be burned in a rocket engine. This kind of in-situ resource utilization would result in massive weight and cost savings to any proposed manned Mars or sample return missions.

• 

The Sabatier reactor uses In-Situ Resource Utilization (ISRU) to create a closed hydrogen and oxygen cycle for life support on planets with CO2 atmospheres such as Mars or Venus.

It contains two chambers, one for mixing and the other for storing a nickel catalyst. When charged with hydrogen and atmospheric carbon dioxide, it produces water and methane. (The similar Bosch reactor uses an iron catalyst to produce elemental carbon and water.)

(ed note: CO₂ + 4 H₂ → CH₄ + 2 H₂O + energy)

A condenser separates the water vapor from the reaction products. This condenser is a simple pipe with outlets on the bottom to collect water; natural convection on the surface of the pipe is enough to carry out the necessary heat exchange.

Electrolysis of the water recovers the hydrogen for reuse.

NASA 2007.

• 

Upon arrival on the Martian surface the ISRU-3 system will begin to generate fuel for the (CM-3/SM- 3/SLV-3) from the atmospheric Carbon Dioxide and on-board cryogenic Hydrogen via the Sabatier process (Figure 41). An optional process of using water electrolysis is possible if significant amounts of trapped/frozen water are found. In this case the PSV-2 could be used as an excavator of the material needed to feed soil/water/frozen CO2 stock material into the Mars ISRU plant.

• 

There has been considerable, if preliminary, investigation into using resources found on Mars to produce propellants to refuel rocket transports. This is part of the larger concept of space settlement called in situ resource utilization (ISRU); essentially “living off the resources of the new lands.” ISRU involves the collection, processing, storing, and use of materials encountered in the course of human or robotic space exploration through full settlement to replace materials that would otherwise need to be brought from Earth at very high cost.

Elon Musk has indicated that SpaceX will exploit this approach to produce the propellants needed to refuel his reusable Big Falcon Rocket (BFR) during Mars transport missions. The BFR propellants include densified liquid methane and oxygen. This series of articles will take a first order engineering look at some of the leading ideas for establishing production plants for the propellants to fuel a BFR on Mars. Also reviewed are associated, potentially marketable, by-products, and especially the energy that may be required for the production processes in the context of emplacement considerations of such a commercial enterprise.

The saying goes that ideas are what could happen, while engineering is about making things happen. So when considering selection and integration of system technologies for the reactant/product recirculation and separation of such a Martian propellant processing plant, many real-life factors, including physics and chemistry, must be the basis for consideration. In this case, this includes addressing separation of ISRU products under relevant operating conditions, regeneration approaches for filters, membranes, and/or sorption beds, the integration of thermal control systems for operation in the colder Mars environment, pressure differences caused by separation processes, and the effects of lower Mars gravity. Specific examples of first order propellant processing plant separation and recirculation engineering design considerations that have already been identified are:

• Carbon dioxide (CO₂) and water (H₂O) harvesting from the Martian environment and their purification (with possible importation augmentation);
• Generation of methane (CH₄) from ISRU carbon dioxide and obtaining hydrogen for use in a Sabatier processor subsystem;
• Water separation from >250°C exhaust hydrogen and methane in a Sabatier subsystem or from carbon dioxide and carbon monoxide (in a reverse water gas shift processor subsystem);
• Water and carbon dioxide electrolysis processing and operating option needs;
• Carbon dioxide/carbon monoxide (CO) separation from 350°C (in a reverse water gas shift subsystem) or up to 900°C (solid oxide electrolysis) stream of mixed gases with recycling of carbon dioxide;
• Hydrogen (H₂)/methane separation post water separation with recycling of the hydrogen;
• Removal of water from saturated oxygen gas (O₂) and methane product streams before liquefaction of the products;
• Overhead power including recirculation pumps and compressors that operate continuously exposed to the Mars environment.

It should be pointed out that NASA’s NextSTEP-2 program seeks to investigate ISRU space resource utilization technology.¹ Their vision is to progress from our current “Earth-reliant” approach to exploration and eventually become “Earth independent” in space. NextSTEP uses a public-private partnership model that seeks commercial development of deep space exploration capabilities to support more extensive human spaceflight missions in and beyond cislunar space. NASA anticipates that the results of these efforts over the ensuing years will provide the needed engineering details for full-up ISRU system developments.

1. Sabatier Processing Subsystem: The Sabatier methanation reaction has been recommended by many of the top researchers as the most likely basis for an ISRU propellant production processing plant on Mars. This is driven primarily because this process can exploit the extremely high availability of carbon dioxide in the Martian atmosphere to create both the methane fuel and water, which can be broken down into useful hydrogen and the oxygen oxidizer needed to run the BFR engines.

CO₂ (g) + 4H₂ (g) ⇋ CH₄ (g) + 2H₂O (g)
ΔH = –165.0 kJ

The Sabatier reaction or Sabatier process was discovered by the French chemist Paul Sabatier in the 1910s. It involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400°C) and pressures in the presence of a catalyst to produce methane and water. Nickel or, more optimally, ruthenium on alumina (aluminum oxide) acts as the catalyst.² The methane gas is the end propellant product. The water produced acts as the feedstock for later propellant plant processing and other process products.

Since the Sabatier reaction occurs rapidly enough to be useful at about 400°C, a source of heat is needed to get the reactor up to its operating temperature. This will likely be provided by some form of an electric heater. Fortunately, once started, the reaction produces its own thermal energy. This means that, except for reactor conductive losses and process thermal management makeup, once the initial temperature is achieved, the reaction provides the majority of the heat to continue the reaction. So this part of the process is not continuously demanding high energy input.

For this first order analysis it is assumed that the energy for this initial reactor start-up has already been expended and loss make-up is low so that it is not a driving requirement to the conceptual design. Instead it will be booked for more detailed consideration during detailed design engineering.

The low temperatures on Mars also mean that careful design attention to proper insulation of the reactor for thermal management is required. Also, as with any chemical reaction, continuous process control monitoring will be needed in the subsystem design to maintain reaction temperatures within optimal bands to obtain the highest production yields.

Once produced, the Sabatier reactor methane gas product outputs will need to go through a separator to remove process-generated water vapor. The collected water vapor is assumed to be collected, rather than expelled as manufacturing waste. The collected water would be thermally conditioned by taking advantage of the cold Martian atmosphere using exterior radiator to condense the water vapor into liquid water, and then be directed to water storage tank(s) for later processing or product sale.

Design and management for liquid water storage tanks needs to carefully consider. This is driven by the average recorded temperatures on Mars of –63°C. These Martian temperatures are well below the freezing temperature of water. Further, this temperature varies from a maximum temperature of 20°C and a minimum of –140°C at the polar regions depending on time of year and distance from the equator. Consideration of the local conditions in which the plant will operate are important input design factors in engineering of the heat exchanges, pipe insulation requirements, and thermal management subsystem design.

A rigorous design process will use heat exchanges and water circulators to tap the incoming warm water vapors from the Sabatier process to help maintain the water in liquid form. For purposes of this study, the energy necessary for circulating pumps is anticipated to be minimal, compared to other primary demands in the processing. The circulating pumps should thus account for a minimal amount of overhead energy estimated in the processing plant budget.

The Sabatier process needs a source of free hydrogen to react with the carbon dioxide to produce methane. A partial source that can be used to obtain the needed hydrogen is through the electrolysis of the water by-product that results from the Sabatier reactor. Unfortunately, for every 44 kilograms of carbon dioxide that is converted into 16 kilograms of methane in the Sabatier process, you need four kilograms of hydrogen. The Sabatier process only produces 36 kilograms of water in the balanced reaction. This means an external source of additional “make-up” hydrogen is required for continuous reactor processing. Unfortunately, free hydrogen gas on Mars is essentially nonexistent.

Instead, an additional source of water is needed to obtain the make-up hydrogen feed stock for the Sabatier reactor. Potential sources of this water could come either from Mars ISRU or could come as an imported commodity from Earth or other celestial bodies, such as the Moon. Water sourcing and further propellant processing to obtain the needed hydrogen and to produce propellant oxygen oxidizer is covered in section 3 below. (Authors clarification note: For purposes of this first order analysis, the extremely small amounts of water obtained from the Martian atmosphere are an infinitesimal contribution to water supplies needed and are not included in the results).

A 2011 prototype test operation was conducted that harvested carbon dioxide from a simulated Martian atmosphere and reacted it with hydrogen. This test produced methane gas at a rate of one kilogram per day, operated autonomously for five consecutive days maintaining a nearly 100 percent conversion rate. An optimized system of this design massing 50 kilograms “has been projected to produce 1 kg/day of O₂:CH₄ propellant… with a methane purity of 98+% while consuming 700 Watts of electrical power.” Overall unit conversion rate expected from the optimized system is one metric ton of propellant per 17 megawatt-hours energy input.³ So assuming all feedstock is available to feed the processing the power to produce a full load of methane (in gaseous form) for a BFR (240 tons) is estimated to be in the neighborhood of 4.1 gigawatt-hours.

2. Raw Material Sources for Sabatier Process: Before Sabatier reactor production can occur, the raw materials for processing must be obtained. Surveys and spectral findings to date indicate that the carbon dioxide required for the Sabatier reaction is an abundant resource in the Martian atmosphere. Even though the atmospheric pressure on Mars is very low—less than one hundredth of Earth’s—the Martian atmosphere consists of almost 95 percent carbon dioxide. Despite its thin atmosphere, this Martian concentration is almost 20 times as much carbon dioxide as is in an equivalent amount of the Earth’s atmosphere.

However, like on Earth, the Mars atmosphere contains other gasses. In addition to carbon dioxide, the Martian atmosphere also has about three percent nitrogen (N₂) and trace amounts of oxygen and water. (For completeness, it should be noted that there are also miniscule amounts of other gases. These miniscule gases should not impact propellant processing. These include argon, neon, krypton, and xenon.) This means a gas separation system is needed prior to feeding the Sabatier processing to remove nitrogen gases and trace amounts of oxygen and water to obtain processing-quality carbon dioxide purity.

Carbon molecular sieves (CMS) are the method commonly used on Earth in the separation processing of air. CMS’s belong to the activated carbons family and can be obtained by various procedures to create pores narrowing to smaller sizes than 10 angstroms. This allows CMS’s to be used to separate the carbon dioxide from the nitrogen. A desiccant, oxidizing reactive bed or adjusted chill/pressure cycle to freeze out the oxygen and remove water should also be considered as an engineering solution method to separate these trace constituents from the atmospheric carbon dioxide in Martian propellant processing plant designs.

However, with high costs of transport for the various CMS and desiccant materials from Earth, it may be more practical to simply expend the additional power instead using a multi-stage chiller pressure cycle subsystem to separate the Martian atmospheric constituents. An example of this processing is the fractional distillation process. On Earth, this process uses cryogenic air separation units (ASUs) to separate nitrogen, oxygen, and often to co-produce argon. The process separates gases by cooling the gas at specified pressures until the individual gas components condense at a given temperature into a liquid which is then extracted. The downside to using this process is that it is a very energy-intensive operation due to the operation of multiple turbo-compression cycling and associated condensation.

The other primary issue of the raw Martian atmosphere is the presence of moderate to significant amounts of dust. In some cases, dust storms have covered virtually all of Mars. When considering design solutions, the dust removal methods that require minimal maintenance, lowest operating costs, and that will maintain continuous plant intake are most desired. For this reason, remove-and-replace mechanical filters, such as those in home furnaces, are not desirable. Vortex swirl particle separator designs would likely be a better option. Regardless, this dust will need to be removed from the Martian ISRU air intake as well during atmospheric pre-processing.

For purposes of this first order review, the key design selection metric for Mars propellant production is to reduce electrical power needs. Since the CMS units will only require minor ongoing electrical needs, they are used for carbon dioxide atmospheric extraction in this review. The CMS power needs only includes the electricity needed by fans to force the gasses over the CMS materials and dust filtration to remove any dislodged CMS particulates. The CMS electrical needs are accounted for in the propellant plant power overhead budget.

Further, the import costs to transport and the set-up needed for the CMS material in the propellant production facility is assumed to have already been completed. Future engineering detailed design and economic viability investigations should take closer looks at these system engineering factors.

(Author’s additional note: It is interesting to note that with profitable expansion of propellant production, the technology appears to exist for making CMS by using local 3-D printing units and ISRU materials. The additional expenses associated with the electricity for mining, refining, and printing the CMS versus the use of multi-stage chiller pressure cycles will be a design/cost trade for future process expansion selection considerations.)

A key to efficiently designed Martian propellant plant—or, for that matter any off-world processing plant—is that the production system reaction products should not waste potentially marketable or usable manufacturing byproducts. For example, the nitrogen extracted from the atmospheric gas separation processing is a potentially exploitable/marketable product. Nitrogen is often used for flushing of tanks and lines through which other gases pass because it is reactive neutral. Then too, the oxygen and water atmospheric separated byproducts are both potentially valuable feedstock for making propellant oxidizer or for life support. For this reason, designing engineers will need to consider options, means, and costs in any facility design with business analysts to determine the costs to market value of any manufacturing byproducts.

3. Water ISRU Sourcing on Mars: Most space scientists currently agree that vast deposits of water appear to be trapped within the ice caps at the north and south poles of Mars. Frozen water also now appears to lie beneath the Martian surface at lower latitudes. Scientists have discovered a slab of ice they estimate is as large as California and Texas combined in the region between the equator and north pole of the Red Planet. Other regions of the planet may contain undiscovered frozen water as well. Specifically, some of the high-latitude regions seem to boast patterned ground shapes that may have formed as permafrost in the soil that froze and thawed over Martian geologic history.

Water mining on Mars will require the development of its own extraction and processing facility. Shipped in from places like the Moon, water may also be an early economically viable purchase alternative. This imported water would require development of lunar water mining, production, and Martian logistics transport architecture. If such commercial capabilities are in place at the establishment of a Mars BFR propellant plant, a certain amount of imported water might prove cost-effective (or simply unavoidable) during the build-up transition to full ISRU water mining and processing production. The selection and cost-effective balance of water sourcing will require additional future detailed system engineering and business trades plus operational business management monitoring over the production plant’s operating life.

For this first order review, it is assumed that an affordable means of extracting and processing of pure quality water will be identified from Martian ISRU water sources. In a 2016 planning study for NASA to examine Martian ISRU methane/oxygen processing, the use of Martian water ore was investigated.⁴ That study examined four cases of water ore processing. Robotic vehicles, such as the NASA KSC Regolith Advanced Surface Systems Operations Robot (RASSOR) prototype or the OffWorld Inc.⁵ smart robots, are likely candidates for mining the raw “water ore”.

For this investigation’s ISRU review, the NASA study four-kilowatt-hour figure was used for the power estimates used by robotic water extraction/mining unit operations. Including the power needs to then load the water ore and transport this water ore feedstock adds another 25 percent to this number, for a total of five kilowatt-hours to mine 4,150 kilograms of water ore. The 7.5-kilowatt-hour examples from the NASA study were then used for power estimates of the separation and vitalization processing to produce 33 kilograms of refined pure quality water from the mined Martian water-bearing regolith ore. This gives an energy cost of extracting and processing (with an overhead factor) to produce purified water from Martian raw ore materials at an estimate of about 230 watts per kilogram. Using this ISRU water source to make up roughly half of the needed water to fuel the Sabatier processor will require roughly two gigawatt-hours of power to mine, produce, and deliver the makeup hydrogen for a single BFR propellant load.

The next article in this series will cover the remaining propellant production processes, while the third installment will investigate options for producing the power necessary for BFR propellant ISRU-based production.

Endnotes

1. Next Space Technologies for Exploration Partnerships-2 (NextSTEP-2), Appendix D: In-Situ Resource Utilization (ISRU) Technology, Broad Agency Announcement NNH16ZCQ001K-ISRU, Originally Issued by NASA: December 4, 2017.
2. Sabatier reaction, Wickipedia.
3. Zubrin, Robert M.; Muscatello, Berggren (2012-12-15). “Integrated Mars In Situ Propellant Production System”. Journal of Aerospace Engineering. Jan 2013. Vol 26: Issue 1, pp 43–56. doi:10.1061/(asce)as.1943-5525.0000201. ISSN 1943-5525.
4. Mars Water In-Situ Resource Utilization (ISRU) Planning (M-WIP) Study. NASA Briefing, 22 April, 2016, contributors: Angel Abbud-Madrid, David Beaty, Dale Boucher, Ben Bussey, Richard Davis, Leslie Gertsch, Lindsay Hays, Julie Kleinhinz, Michael Meyer, Michael Moats, Robert Mueller, Aaron Paz, Nantel Suzuki, Paul van Susante, Charles Whetsel, Elizabeth Zbinden.
5. OffWorld Web site

(ed note: the analysis below shows how inefficient it is to ship Lunar Water to LEO by using chemical rockets. Naturally it becomes better if you use a propulsion system with a higher exhaust velocity or something like a Lunar Space Elevator or related concept. The latter is what he is referring to when he mentions "propellantless methods")

One of many important issues that doesn’t get enough airtime when discussing lunar In-situ Resource Utilization (ISRU) is how to efficiently get the propellants and other materials off the lunar surface. There seems to be a line of thinking that could be called “all we need is ISRU” that says that lunar ISRU is the most critical technology and everything else is just a distraction.

While it is possible to take propellant produced on the lunar surface up to Low Lunar Orbit (LLO) or to one of the Earth-Moon Lagrange points using similar rockets to what you landed with, and then deliver this to Low Earth Orbit (LEO) using entirely propulsive tugs with no new technology, this isn’t very efficient. You end up spending a significant fraction of the lunar derived propellant lifting both the delivery propellant and the landing return propellant, as well as the propellant to ship the cis-lunar tanker back to LEO and bring it back for refueling near the Moon.

To give you an idea of how inefficient, I’m attaching a spreadsheet with some back-of-the-envelope level calculations to illustrate this point. In the spreadsheet I model a Lunar Surface to LLO or EML-2 and Back tanker, and then an LLO or Earth-Moon Lagrange Point 2 (EML-2) to LEO and Back tanker. In both cases, I assumed they were about Centaur size (~23 tonnes), and used RL-10 based propulsion. For the reusable lunar surface tanker, I gave two propellant mass fractions – 90% (aggressive once you factor in landing hardware) and 85% (more conservative). For the cislunar tanker, I assumed a 90% propellant mass fraction, and also analyzed cases where an aerobrake was provided that weighed 5% of the Gross Takeoff Weight (GTOW) and 10% of the GTOW.

In the most extreme case of “all you need is ISRU” thinking, where you use entirely existing chemical propulsion systems for getting propellants from the lunar surface to LEO, only 9-11% of the propellant produced on the Moon actually makes it to LEO. Alternately, this means you have a “gear ratio” (ratio of propellant extracted on the Moon to propellant delivered to LEO) of 9-11. Not only is this very wasteful, but it means that you would need to size your ISRU capacity significantly higher than if you had a more efficient system.

Of the approximately 12km/s of round-trip Delta-V from the lunar surface to LEO and back, there are several options you can use to improve your gearing ratio, each of which attack a different leg of the journey:

1. Stage and refuel in LLO or EML-1/2 (which was already assumed for this analysis).
2. Aerocapture/braking to go from your Trans-Earth Injection trajectory into LEO
3. Propellantless methods for launching from the lunar surface to LLO, EML-1 or 2, or even directly to LEO.
4. Propellantless methods for landing on the Moon from LLO or EML-1 or 2
5. Propellantless or high-Isp methods for traveling from LEO to LLO or EML-1 or 2.

This series is focused on options #3 and #4, though #2 is also low-hanging fruit (and provides about a 2-3x gear ratio improvement over the baseline “all we need is ISRU approach).

Citizen Joe:

I've found that Jupiter's radiation belt and wind speeds make it unsuitable for direct harvest.

However, that same radiation belt (and corresponding magnetic fields) could be used for 1) power 2) transportation and 3) spallation of useful elements into needed isotopes.

The last one is an interesting prospect from the mineral spewing volcanic Io. I don't actually recommend colonizing Io, but rather maintaining essentially ion farms within the radiation belt. The other moons are suitable for exploration, but Callisto (the outermost Galilean Moon) is protected from the solar winds by Jupiter's magnetosphere while being far enough away to reduce the radiation exposure. So, if I were to set up a Jupiter base/colony it would be there. That base would hold vast subsurface tanks of water for aquacultures and a whole biosystem. Waste heat from the reactors would be used to keep the tanks temperature regulated and the whole environment could be expanded in a modular manner depending on the waste heat requirements.

Fun fact: It takes two weeks to get receive the same radiation dose on Callisto that you receive on Earth every day. Moving in to Ganymede (the next closest moon) you would get week's dose of radiation in one day.

Resource harvesting is a major draw for investment in space. Two main classes of resources are important in the near term, with three additional classes becoming important in future decades.

First up is water. It is perhaps the easiest substance to extract and purify and is thought to be abundant in chondrite asteroids. It is also present on the Moon, Mars and Ceres, though Mars is an unlikely source of water for shipment back to LEO. Water can be split to provide oxygen for breathing gas or oxidizer and hydrogen for propellant or other chemical uses (Sabatier process for life support or as a fuel cell input for electricity). There is an immediate market for potable water on the ISS and will presumably be a strong market at any future space station. Water depots are another potential customer assuming future satellite RCS transitions from hypergolics to electrolyzed water.

Next is rare elements, mainly platinum group metals. These are abundant in metallic asteroids, with asteroid 16 Psyche alone representing perhaps 110 billion tons of PGM (at 5 PPM). Early efforts will probably focus on bodies of 100-200 meter diameter rather than 200+km diameter, but the supply is out there. Some detractors claim that dumping tons of precious metals on the market will crash prices. Certainly prices will go down if a new and abundant supply comes online, but platinum's value comes from more than being shiny. There are many potential uses for platinum that are not cost-effective today. A massive increase in supply would lead to a technological expansion of similarly massive proportions. Regardless, there is an immediate market for PGMs and other rare elements on Earth; any operator that can land their payload safely will be able to sell it easily any time they choose.

The latter categories are a bit similar. First is construction materials like iron, nickel and other metals (aluminum, calcium, magnesium, titanium, cobalt, tungsten) that might be used to build structural parts and pressure vessels. Next is semiconductors and dopants, mostly silicon but including gallium, germanium and indium plus tin, arsenic, antimony, aluminum, phosphorus, boron and gallium. These would be used to build solar panels, LED lights and potentially microprocessors. Last is whatever is left over, the slag from other processing. This is generally useful for radiation shielding (as is water) and would be used for manned craft and facilities outside Earth's magnetic field. A fourth category might be carbon and any trace nutrients required for plant life, though these materials would be separated as part of the refining process for structural metals and high-purity semiconductors.

All of the latter categories require a significant presence in orbit with the capacity to manufacture complex parts. This is definitely not a near-term environment, so the 'early days' operators are reduced to just water and platinum as potential products. Given the significant complexity involved in extracting platinum, I expect water to be the first non-Earth resource sold.

WATER! IS! NOT! RARE! PAST! THE! SOLAR! SYSTEM'S! FROSTLINE!

• 

The Frost Line is the point where water ice remains frozen during the formation of the solar system. For our solar system this has been calculated to be from 2.7 Astronomical Units to 3.1 AU.

The Snow Line is the present distance at which water ice can be stable (even under direct sunlight). For our solar system this has been calculated to be 5.0 AU.

B_snowLine = sqrt( S_lumBolo / 0.04)

where:

B_snowLine = start of snow line (Astronomical Units)
S_lumBolo = Bolometric Luminosity
sqrt(x) = square root of x

Multiply AU by 150,000,000 to convert into kilometers

Momentus Space is a space tech company offering a ‘water plasma rocket’ – basically a helicon thruster that uses water as propellant (not ‘fuel’ as the energy has to be added via a power source). A helicon thruster is an electrodeless electric thruster that uses microwave energy from a ‘helicon’ antenna to flash heat the propellant into plasma. As the hot water doesn’t touch the electrode supplying the energy, there’s no corrosion of the drive system. Thus it can run for long, long periods of time. The water plasma (ions of hydrogen, oxygen and hydroxide plus their loose electrons) rushes out and produces a Specific Impulse (I_sp) of 700 seconds in the small initial system being marketed. That’s better than burning hydrogen and oxygen to make hot fast steam, like a Space Shuttle Main Engine, which typically gets about 460 seconds I_sp in space. And most long term propellant mixes that store well in space, like monomethyl hydrazine+nitrogen tetroxide, manage about 300 seconds.

But… there’s a down-side to all electric rockets. Power has to be supplied to the engine and it’s a LOT. Unlike chemical fuels, which react to release the energy they store, an electric rocket needs electrical power to turn Propellant into Push (3 P’s, Power-Propellant-Push). An I_sp of 700 seconds translates into an effective jet velocity of about 6,865 m/s, which means a kinetic energy of 23.6 megajoules per kilogram of propellant shot out the back of the drive. Jetting that 1 kilogram in a second at 6,865 m/s produces a push (an impulse) of 6,865 newton-seconds. If the satellite+rocket combination masses 300 kilograms, then it’d accelerate at 6,865 kg.m/s² / 300 kg = 22.9 m/s², which is probably excessive for a satellite already in orbit. It’d also require powering the jet with at least 23.6 megawatts of power – and probably more like 32 megawatts of power, if we take rocket efficiency into account.

If we dial down the impulse per second to just 1 newton, rather than 6,865, then the acceleration would be a leisurely 3.33 mm/s² and the power needed more like 4.5 kilowatts. That’s still a lot, but more feasible to provide. If half the mass on board is propellant, then the total time to use it is 12 days. The mass-ratio of empty to full is 2. Thus, thanks to the Rocket Equation, we can compute the total delta vee as LN(2) x 6,865 m/s = 4,758 m/s. If we start in Low Earth Orbit (LEO) that’ll get us much of the way to Geosynchronous Earth Orbit (GEO), but much of the time will be spent in the worst bits of the Van Allen radiation belts. The satellite can be hardened to take the punishment, but it eats into the actual ‘payload’ we’re delivering to its new orbital home.

The other option, if we’re using water, is to turn it into hydrogen and oxygen, to then fill up a rocket that can burn it at high thrust and deliver our GEO bound satellite in mere hours rather than days (NB: most available electric rockets would actually take months, due to their higher power demands and smaller thrust.) If we react hydrogen and oxygen to make water, then the energy released per kilomole (18.015 kilograms of H₂/O) is 241.83 megajoules. That’s 13.42 megajoules per kilogram of fuel mix. So the reverse process, breaking water into hydrogen and oxygen, means applying at least that much to water to break it apart. The usual process assumed is electrolysis, which uses electrical potentials to break up the water molecules, and it’s typically 70-80% efficient. Then the resulting gases need to be cooled and compressed into liquid form so they can stored. Total is 15.33 megajoules per kilogram. At 80% efficiency that means 19.16 MJ/kg.

An Orbital Fuel Depot, splitting water to make fuel, powered by ~20 megawatts, would then make 1 kilogram of fuel per second, thus over 30,000 tons per year. That’d deliver about 20,000 tons of annual payload to GEO, which is much more than present traffic levels. If there’s about 450 active GEO satellites, with average lifespans of 15 years, and each masses about 6 tons, then 30 replacement satellites need to be launched each year, thus about 300 tons of fuel per year is a good starting goal.

A side note: At the end of its useful life, of about 15 years, a GEO satellite is then is parked in a higher orbit – a ‘graveyard orbit’ – to open orbital space for functional satellites. At least if the satellite owners are responsible corporate citizens.

Thus the Orbital Fuel Depot needs about 0.2 megawatts of power to provide fuel for Space Tugs serving the GEO satellite trade. If we use solar power, that’d be the largest single array ever launched, but it doesn’t have to be heavy. Reflectors that concentrate sunlight onto high temperature solar cells can minimise the mass and the total area of expensive semi-conductors such solar cells are made of.

Question is: What’s the best source for the water?

Of course Earth might seem a logical choice. The Throw-Away Falcon Heavy promises about 60 tons of payload to LEO. Thus 5 Falcon Heavies per year could supply the water. Total RP-1/LOX propellant required 1,400 × 5 = 7,000 tons. Fully Reusable Falcon Heavies might deliver 30 tons to LEO, so 10 launches of those would be enough. Some 14,000 tons of RP-1/LOX. A bit further along and the Big Falcon Rocket promises 100 tons to LEO. Just 3 launches required, but about 4,000 tons of LCH₄/LOX required per BFR, thus 12,000 tons total. Another option is to mine water on the Moon, then deliver it to LEO via H₂/O₂ rockets. A Moon Tug could launch from the surface into an Earth Transfer Orbit for a delta-vee of about 2.5 km/s with aerobraking into LEO. The Moon Tug plus a payload of 100 tons water masses about 120 tons, but needs about 173 tons of H₂/O₂ to launch from the Moon, then return the empty Tug to the Moon. That does put the whole process into question, since supplying 300 tons of water in LEO to make into H₂/O₂ also means having to make about 519 tons of the same to use on the Moon. Thus about 2.5 megawatts of power supply delivered to the Moon. That might not be excessively onerous, especially if the Moon’s regolith (‘soil’) can be turned into solar panels as some have suggested.

Momentus Space’s Water Rocket becomes relevant at this point. If the Moon Tug delivers water to a waiting Water Rocket in Low Lunar Orbit (LLO), which then returns it to LEO via aerobraking, then it only needs about 100 tons of H₂/O₂ for every 100 tons water delivered. The orbital design will require some finesse. Low thrust orbits aren’t like high-thrust orbits. The total delta-vee required is significantly higher. In the case of the LEO-to-LLO round-trip mission, the total delta-vee can be up to 18.8 km/s, which would be a prohibitive additional water cost. That’s LEO-to-LLO and back, solely under thrust. So rather than thrusting the whole way, the Water Rocket thrusts away from LLO into Earth’s Sphere of Influence and a low perigee aerobraking orbit, the delta-vee I’m assuming is more like 2 km/s one-way. Getting back to the Moon however incurs the low-thrust delta-vee penalty, but only the Water Rocket is returning, sans 100 tons of payload. The return delta-vee could be up to ~9.4 km/s, but hopefully it’ll be less via careful orbital design. Alternatively, we might make water containers that can aerobrake themselves, and then be repurposed as pressure vessels in LEO once emptied. The Water Rocket could then free-return to the Moon after delivery, so long as perigee isn’t too low.

Chief product for Space Tug operators in LEO is water decomposed into H₂ and O₂. However the stoichometric mix of decomposed water is deficient in water. The mass ratio of the O/H₂ is 15.9994 / 2.016 = 7.9362. High performance rocket engines run on a 6:1 mix, thus leaving an excess of oxygen. First thought is to sell it for breathing gas, but that’s a lot more than the ISS needs. However what if a bit of the hydrogen is reacted (very carefully with catalysts in CO₂ solvent) with the oxygen to make hydrogen peroxide? By itself hydrogen peroxide is a pretty good monopropellant, getting up to 180 seconds Specific Impulse (I_sp). Mixed with a bit of ethanol and it’s even better. The usual space-storable monopropellant is hydrazine, which is toxic and nasty. Hydrogen peroxide, in spite of its shortcomings, is nowhere near as bad.

The other market for lunar products is On-Orbit Servicing of existing GEO Satellites. While hydrogen peroxide makes for a decent replacement for hydrazine – given the right engines, so there’d need to be some retrofitting – Water Rockets, which are water propellant-using helicon thrusters, might be even better for station-keeping in the long term. The higher Isp means the refueling schedule is less frequent. The fact that the market is in GEO means the gravity a low thrust system struggles against is reduced more than 40-fold. Water Rockets could service GEO from LLO. Space Tugs could also be stationed in GEO, refueled from a Water-to-Fuel Facility based in GEO. The delta-vee to an aerobrake orbit to LEO is about 1.5 km/s, with about 0.08 km/s to then circularise in LEO parking orbit to meet the cargo. Then a high-thrust burn for Geosynchronous Transfer Orbit (GTO) to carry a Comm-Sat to its new home.

And the peroxide? On the Moon it actually makes for a decent energy storage system during the 14 days Lunar night. Peroxide powered high efficiency turbines can provide power for whatever night time activities a mostly Solar powered Water Mine will engage in. Perhaps that’s when most of the science activities the Base facilities can be hired out for will take place.

• 

The closest place to look is Luna. Unfortunately data from the Apollo moon missions suggested that the lunar regolith was drier than an old slab of concrete lying in the Sahara desert. Luna's "day" is 27 or so Terran days long, exposing Luna's surface to the merciless rays of the Sun and baking it to an oven-like temperature of 390°K. Any water-ice on the surface would have evaporated into space a long time ago. Even if an occasional water-ice comet smacked into Luna, the Sun's rays would make it go away.

But wait a minute. What if there were places on Luna that were permanently in shadow? Since there is no appreciable atmosphere, an area in Lunar shadow can drop down to a frigid 35°K. Any comet-ice that landed in such a deep-freeze would be preserved quite nicely.

The walls of lunar craters will provide shadow for part of the lunar day, but eventually the sun will be over head, the shadow will vanish, and the comet ice will evaporate. Except for at the lunar north and south poles. There the angle is steep enough that the sun's rays never penetrate the interior of the craters. See the picture, it shows the illumination of the lunar south pole over an entire lunar day. The dark areas are always dark. Any ice deposited there will still be there, patiently waiting for thirsty lunar colonists.

Lo and behold, it is there!

In In September 2009, India's Chandrayaan-1 space probe got a fleeting glimpse of lunar water-ice. In November 2009, NASA's LCROSS space probe watched as its spent upper stage violently crashed into the lunar south pole at 10,000 km/h, spotting ice crystals in the explosion. Finally in March 2010 the Chandrayaan-1 observed a bit of ice in the lunar north pole, a bit over 600 million tonnes of nearly pure water ice.

The lunar poles are going to be valuable real estate.

• 

Water reserves found on the moon are the result of asteroids acting as "delivery vehicles" and not of falling comets as was previously thought. Using computer simulation, scientists from MIPT and the RAS Geosphere Dynamics Institute have discovered that a large asteroid can deliver more water to the lunar surface than the cumulative fall of comets over a billion year period. Their research is discussed in an article recently published in the journal Planetary and Space Science.

At the beginning of the space age, during the days of the Apollo program, scientists believed the moon to be completely dry. At these earliest stages in satellite evolution, the absence of an atmosphere and the influence of solar radiation were thought enough to evaporate all volatile substances into space. However, in the1990s, scientists obtained data from the Lunar Prospector probe that shook their confidence: the neutron current from the satellite surface was indicative of a larger fraction of hydrogen at the near-surface soil of some regions of the moon, which one could interpret as a sign of the presence of water.

In order to explain how water could be kept on the moon's surface, scientists formulated a theory known as "cold traps." The axis of the moon's rotation is nearly vertical, which is why in the polar regions there are craters with floors that are never exposed to sunlight. When comets consisting mostly of water ice fall, evaporated water can gravitate into those "traps" and remain there indefinitely, as solar rays do not evaporate it.

In recent years, lunar missions (the Indian Chandrayan probe, the American LRO, data from the Cassini probe and Deep Impact) have brought scientists two pieces new information. The first is that there are indeed considerate quantities of water and hydroxyl groups in the near-surface soil on the moon. The LCROSS experiment, in which a probe purposely crashed onto the moon resulting in the release of a cloud of gas and dust that was later studied with the use of a spectrometer, directly confirmed the existence of water and other volatile substances. The second piece of new information came when the Russian LEND apparatus mounted on board LRO generated a map of water distribution on the moon's surface.

But this second piece has only partly proven their theory: the map of "cold traps" did not correspond to the map of water deposits. The scientists had to refine the theory, and the idea of "lunar congelation" was proposed. It allowed accepting that "survival" of water ice in the regions exposed to sunlight is possible under a soil blanket. It was also suggested that a substantial part of "water" seen by the probes is implanted solar wind: hydrogen atoms from solar wind react with oxygen atoms and form an unstable "dew" of water molecules and hydroxyl groups. Scientists left the possibility open that water could exist in a bound state, i.e. in hydrated minerals.

There was still the matter of determining how water had appeared on the moon and how much of it there could be. At the same time, another issue may prove to be of practical importance in the coming years: if manned stations are to be constructed on the moon in the nearest future, we should know what kind of resources we can count on, preferably before construction begins.

Vladimir Svettsov and Valery Shuvalov, who have been researching the fall of comets and asteroids, including the computerized simulation of the Tunguska catastrophe as well as the Chelyabinsk meteorite fall, decided to develop the most probable mechanism of water delivery to the moon and an approximate the "supply" volume. For this they used the SOVA algorithm, which they created themselves, for the computerized modelling of the fall of cosmic bodies onto the surface of the moon. Each body had its own velocity and its own angle of fall. In particular, at the output, the model demonstrated the distribution of maximum temperatures when the falling body's mass heated up during impact as well as its dynamic.

The scientists first decided to check whether the comets are able to fulfill the role of main "water suppliers." The typical velocity of an ice comet ranges from 20 to 50 km per second. The estimates suggested that such a high impact velocity causes from 95 to 99.9 percent of the water to evaporate into space beyond retrieve. There is a family of short-period comets whose velocity of fall is much lower - 8-10 km per second. Such short-period comets account for about 1.5 percent of lunar craters. Nevertheless, the simulation has shown that when these short-period comets do fall, almost all the water evaporates and less than 1 percent of it remains at the impact point.

"We came to the conclusion that only a very small amount of water that arrives with a comet stays on the moon, and from this decided to explore the possibility of an asteroid origin of lunar water," Shuvalov says.

The scientists decided to take a closer look at asteroids and found that they consist of initially non-differentiated construction materials of the solar system and contain a rather considerable proportion of water. In particular, chondrite carbonaceous, the most common type of asteroids and meteorites, can contain up to 10 percent water.

However, water in chondrites is effectively protected: it is in a chemically bounded condition, and it is "blocked" in a crystal lattice of minerals. Water starts to seep out only when it is heated to 300-1200 degrees centigrade depending on the type of hydrous mineral. This means that it has the potential of remaining in the crater together with the asteroid.

The simulation has also revealed that when the velocity of fall is 14 km per second and the angle of fall is 45 degrees, about half of the asteroid's mass will never even reach the fusing temperature and remains in a solid state. One-third of all asteroids that fall on the moon have a velocity of less than 14 km per second just before impact. When this happens, the major part of the fallen body remains in the crater: 30-40 percent is left after an oblique impact, and 60-70 percent after a vertical one.

"We've concluded that the fall of asteroids containing water could generate "deposits" of chemically bounded water inside some lunar craters," Shuvalov says. "The fall of one two-kilometer size asteroid with a rather high proportion of hydrated minerals could bring to the moon more water than all of the comets that have fallen over billions of years," he adds.

Calculations reveal that around 2 to 4.5 percent of lunar craters could contain considerable supplies of water in the form of hydrated minerals. They are stable enough to contain water even in areas exposed to the Sun.

"That is very important because the polar cold traps are not very convenient areas for the construction of lunar bases. There is a small amount of solar energy and it is difficult to organize radio communication and, lastly, there are dramatically low temperatures. The possibility of obtaining lunar water in regions exposed to the Sun could make the issue of satellite exploration much easier," concluded the scientist.

• 

     Once again he stared intently at the excellent photographs of the Chinese ship, taken when it had revealed its true colours and was just about to leave Earth orbit. There were later shots — not so clear, because by then it had been far away from the prying cameras — of the final stage as it hurtled toward Jupiter. Those were the ones that interested him most; even more useful were the cutaway drawings and estimates of performance.

     Granted the most optimistic assumptions, it was difficult to see what the Chinese hoped to do. They must have burned up at least ninety per cent of their propellant in that mad dash across the Solar System. Unless it was literally a suicide mission — something that could not be ruled out — only a plan involving hibernation and later rescue made any sense. And Intelligence did not believe that Chinese hibernation technology was sufficiently far advanced to make that a viable option.

     But Intelligence was frequently wrong, and even more often confused by the avalanche of raw facts it had to evaluate — the 'noise' in its information circuits. It had done a remarkable job on Tsien, considering the shortness of time, but Floyd wished that the material sent to him had been more carefully filtered. Some of it was obvious junk, of no possible connection with the mission.

     Nevertheless, when you did not know what you were looking for, it was important to avoid all prejudices and preconceptions; something that at first sight seemed irrelevant, or even nonsensical, might turn out to be a vital clue.

     With a sigh, Floyd started once more to skim the five hundred pages of data, keeping his mind as blankly receptive as possible while diagrams, charts, photographs — some so smudgy that they could represent almost anything — news items, lists of delegates to scientific conferences, titles of technical publications, and even commercial documents scrolled swiftly down the high-resolution screen. A very efficient industrial espionage system had obviously been extremely busy; who would have thought that so many Japanese holomemory modules or Swiss gas-flow microcontrollers or German radiation detectors could have been traced to a destination in the dried lake bed of Lop Nor — the first milepost on their way to Jupiter?

     Some of the items must have been included by accident; they could not possibly relate to the mission. If the Chinese had placed a secret order for one thousand infrared sensors through a dummy corporation in Singapore, that was only the concern of the military; it seemed highly unlikely that Tsien expected to be chased by heat-seeking missiles. And this one was really funny — specialized surveying and prospecting equipment from Glacier Geophysics, Inc., of Anchorage, Alaska. What lamebrain imagined that a deep-space expedition would have any need — the smile froze on Floyd's lips; he felt the skin crawl on the back of his neck. My God — they wouldn't dare! But they had already dared greatly; and now, at last, everything made sense.

     He flashed back to the photos and conjectured plans of the Chinese ship. Yes, it was just conceivable — those flutings at the rear, alongside the drive deflection electrodes, would be about the right size.

     Floyd called the bridge. 'Vasili.' he said, 'have you worked out their orbit yet?'
     'Yes, I have,' the navigator replied, in a curiously subdued voice. Floyd could tell at once that something had turned up. He took a long shot.
     'They're making a rendezvous with Europa, aren't they?'
     There was an explosive gasp of disbelief from the other end. 'Chyort voz'mi! How did you know?'
     'I didn't — I've just guessed it.'
     'There can't be any mistake — I've checked the figures to six places. The braking manoeuvre worked out exactly as they intended. They're right on course for Europa — it couldn't have happened by chance. They'll be there in seventeen hours.'
     'And go into orbit.'
     'Perhaps; it wouldn't take much propellant. But what would be the point?'
     'I'll risk another guess. They'll do a quick survey — and then they'll land.'
     'You're crazy — or do you know something we don't?'
     'No — it's just a matter of simple deduction. You're going to start kicking yourself for missing the obvious.'
     'Okay, Sherlock, why should anyone want to land on Europa? What's there, for heaven's sake?'
     Floyd was enjoying his little moment of triumph. Of course, he might still be completely wrong. 'What's on Europa? Only the most valuable substance in the Universe.'
     He had overdone it; Vasili was no fool, and snatched the answer from his lips. 'Of course — water!'
     'Exactly. Billions and billions of tons of it. Enough to fill up the propellant tanks — go cruising around all the satellites, and still have plenty left for the rendezvous with Discovery and the voyage home. I hate to say this, Vasili — but our Chinese friends have outsmarted us again.

---

     The ship had touched down, after its initial survey, on one of the few islands of solid rock that protruded through the crust of ice covering virtually the entire moon. That ice was flat from pole to pole; there was no weather to carve it into strange shapes, no drifting snow to build up layer upon layer into slowly moving hills. Meteorites might fall upon airless Europa, but never a flake of snow. The only forces moulding its surface were the steady tug of gravity, reducing all elevations to one uniform level, and the incessant quakes caused by the other satellites as they passed and repassed Europa in their orbits. Jupiter itself, despite its far greater mass, had much less effect. The Jovian tides had finished their work aeons ago, ensuring that Europa remained locked forever with one face turned toward its giant master.

     All this had been known since the Voyager flyby missions of the 1970s, the Galileo surveys of the 1980s, and the Kepler landings of the 1990s. But, in a few hours, the Chinese had learned more about Europa than all the previous missions combined. That knowledge they were keeping to themselves; one might regret it, but few would deny that they had earned the right to do so.

     What was being denied, with greater and greater asperity, was their right to annex the satellite. For the first time in history, a nation had laid claim to another world, and all the news media of Earth were arguing over the legal position. Though the Chinese pointed out, at tedious length, that they had never signed the '02 UN Space Treaty and so were not bound by its provisions, that did nothing to quell the angry protests.

---

     'But Europa's canals aren't an illusion, though of course they're not artificial. What's more, they do contain water — or at least ice. For the satellite is almost entirely covered by ocean, averaging fifty kilometres deep.

     'Because it's so far from the sun, Europa's surface temperature is extremely low — about a hundred and fifty degrees below freezing. So one might expect its single ocean to be a solid block of ice.

     'Surprisingly, that isn't the case because there's a lot of heat generated inside Europa by tidal forces — the same forces that drive the great volcanoes on neighbouring Io.

     'So the ice is continually melting, breaking up, and freezing, forming cracks and lanes like those in the floating ice sheets in our own polar regions. It's that intricate tracery of cracks I'm seeing now; most of them are dark and very ancient — perhaps millions of years old. But a few are almost pure white; they're the new ones that have just opened up, and have a crust only a few centimetres thick.

     'Tsien has landed right beside one of these white streaks — the fifteen-hundred-kilometre-long feature that's been christened the Grand Canal. Presumably the Chinese intend to pump its water into their propellant tanks, so that they can explore the Jovian satellite system and then return to Earth. That may not be easy, but they'll certainly have studied the landing site with great care, and must know what they're doing.

     'It's obvious, now, why they've taken such a risk — and why they should claim Europa. As a refuelling point, it could be the key to the entire outer Solar System. Though there's also water on Ganymede, it's all frozen, and also less accessible because of that satellite's more powerful gravity.

• 

The Nationalists had sponsored a tax on exported ice, arguing that those who depleted Luna’s natural resources should be made to pay for the privilege. The argument had struck a responsive chord with Lunarians. Compared to the surface of the Moon, the Sahara Desert has a flooding problem. Little wonder that the inhabitants had strong feelings about water.

It did not help that they could see an unlimited supply of the stuff hanging directly overhead. Although Earth’s stock was vastly greater than Luna’s was, its deep gravity-well made tanking water to orbit impractical. Luna’s weak gravity had thus made it the largest exporter of ice in the Solar System (at least until the Phobos mines become operational).

Luna’s tax had come as a shock to the space habitats. Besides its obvious uses, water was the raw material from which oxygen and hydrogen were electrolyzed. The Lunar tax had doubled The Rock’s yearly cost for consumables. Despite this, Thorpe could not really blame the Lunarians. For, unlike the people of Earth, those who lived beyond the atmosphere knew the value of a kilo of ice.

---

Hobart leaned back in the lounger and clasped his hands across his midsection. “Some people have likened Luna to a giant mining concern. We tunnel everywhere. We tunnel after ice deposits, are forever hollowing out new living volume, and dig for those metals we need for our industries. We get our metals from the same source as Sierra Corporation. We mine asteroids for them. The difference is that your asteroid is free flying, while ours crashed down on the Moon billions of years ago.

“Because of all this tunneling, we find ourselves perennially short of heavy mining equipment. Despite all our efforts, the equipment manufacturers never seem to catch up. Therefore, we are forced to ration the machinery we devote to ice mining, habitat construction, and metals extraction. In order to increase the production of one commodity, we have to cut back in the other two areas.

“Ice is critical to us, Mr. Thorpe. The health of our economy depends on it. It is the source of our water, air, and much of our chemical fuel. At the moment, our inability to expand ice production is stifling our economic growth.”

“Build more heavy machinery.”

“That requires additional factories, which require additional resources we don’t have. What do we do without while we are building the factories? No, we need something which will boost ice production over the short term.

---

“I’ve been studying the economics of ice mining. There is a very large market for it everywhere in space. I remembered something you wrote in your thesis on asteroid mining. You said that the early mines in the asteroid belt would not have failed if their product had been worth just five times more than it was.”

“So, ice is ten times more valuable than iron! By your calculations, it is the one thing that can be shipped interplanetary distances at a profit. Anyway, I took a chance that you might want to get into the ice mining business. You can always say that I exceeded my authority and denounce the whole deal.”

• 

• 

• 

I was thinking that hypothetical asteroid miners would like a source of heavy metals, the sort of thing you'd find in M-type asteroid.

I made the uninformed assumption that Mom-and-Pop operations are generally limited to mining volatiles, mining metals is a job for the big corporations with deep pockets.

I made the uninformed assumption that a huge asteroid-mining megacorporation may want to corner the market in such mine-able elements. I made the further uninformed assumption that a nickel-iron asteroid would also be more likely than other types to contain a small percentage of even heavier elements, which would increase the asteroid's value. Obviously when you are dealing with a percentage: the bigger the total mass, the bigger the mass of the percentage. If you are dealing with atomic rockets that want fissionable elements for fuel, it would be nice to have a source other than Terra. For literary dramatic purposes.

Anyway, this suggest to me that all the asteroid-mining megacorporations would like to control the asteroid 16 Psyche. Let's face it: blasted asteroid is the mother-lode.

Psyche contains about 1% of the mass of the entire freaking asteroid belt. And it ain't a worthless rock pile. Spectroscope says the surface is 90% metallic nickel-iron, with about 6% orthopyroxene. Astronomers figure it is a fragment of a planetary metallic core.

---

Again, assuming the megacorporations want to control the entire asteroid, they will constantly be battling each other to either seize or maintain control of Psyche. By means fair or foul, in space between battlefleets, in the corporate world with hostile take-over bids, whatever it takes.

Plus I'm sure some national governments would like to seize control as well.

---

As a side note: consider that raw ore or refined elements need to be shipped to their markets. One possibility is by using mass drivers. These are installations on or orbiting Psyche that hurl engine-less ore cannisters to waiting customers.

A second side note: under some circumstances it would be more cost-efficient to locally refine the raw ore into purified elements before shipping. One possibility is by laser zone refining.

A third side note: if you ever read Heinlein's The Moon Is A Harsh Mistress you know that cargo mass drivers are also kinetic energy weapons of mass destruction. And a zone refining laser is after all a very powerful laser.

Add the fact that the Psyche mining installation belonging to whichever megacorporation currently owns Psyche may be attacked by a rival corporation's battlefleet at any moment and I think you can see where this is heading.

When an attack comes, installations that use large amounts of energy can be quickly re-purposed into defensive weapons. High velocity cargo cannisters can smash invading spacecraft like sledge-hammers splattering cockaroches, and high-energy laser beams can drill white-hot holes in enemy ships long-ways. And these defensive weapons will not lie idle in between battles, which will keep the corporation bean-counters happy. Any rival corporation will need to cope with these defenses, somehow.

And not necessarily by increasing the size of the invading fleet. There are possibilities of infiltration by covert teams to commit sabotage, or inserting corporation moles into the employees of Psyche Base.

---

I asked the Google Plus mass-mind if they could think of other implications or elaborations of this scenario and was gratified by the responses.

NATHANIEL HULL:

     Some mega-corp trying to move or redirect the mass and the consequences thereof. Or the opposite, driving smaller asteroids into the larger, threatening the operations of rival companies with being crushed by space debris.

DEAN CALAHAN:

     I would want to have stealth refiners/launchers that would shoot off stealthed bits of Psyche under everybody's nose. I might need some mom-n-pop carbon to blacken my operations/payloads.

SEVORIS DOE:

     There may be inner system solar power supply plattforms (read, big solar arrays and transmission masers/lasers) to power mining facilities, beamliners and enable ablative mass propulsion via transmission masers and coupled lasers.
     These same facilities can be used to move, h-hmm, "material acquisition vehicles" (read, Payload Hijackers), deflect the trajectory of mass driver payloads with sufficient ablative remass, mess with their trajectory discretely just because, and generaly be used as tools of corporate negotiation. They could also be used, for example, to blind telescopes or jamm laser comms.
     I‘d also expect some international mission, or a few national space forces, to enforce tight laws near national holdings. Not nessecarily involving themselves in the corporate struggles, but ensuring that corp shenanigans don‘t touch the Earth-Luna sphere or Mars, I‘d imagine.

JASON FRITZ:

     More plausible: Multiple entities mining the rock at the same time, each trying to infringe on the others zones. Each engaging in increasingly risky techniques to mine/process the ore in their sector as quickly as possible before it can be stolen or mined from underneath them. Lots of political lobbying to increase their own zone/decrease the size of a rival's zone. Creation of multiple shell companies/subsidiaries to gain access to multiple zones.
     Eventually a huge, ungainly oversight system is set up to make sure that all actors are "playing by the rules," which completely eliminate smaller operators from the market via outrageous barriers to entry, resulting in a somewhat stable oligopoly. Those involved in the oligopoly are happy to continue the status quo as long as their share of the ore is protected by the oversight system. A large shipping/processing industry develops around the asteroid, each with its own layer of fees and tariffs before the final material reaches the planet.
     Piracy is the primary means to gain access to the metal if you exist outside the oligopoly. Why attack the asteroid and try to "hold ground" when you can swoop in as the metal makes the transit back to Earth/Mars? Shipments wouldn't be stolen as much as held hostage as it is difficult to move a couple million tons of process iron/nickel. Some piracy is state sponsored, some is undertaken by corporations in the oligopoly. Some of it is overlooked as "the price of doing business, some is met with harsh reprisals, especially by smaller actors or upstarts that aren't playing ball/giving a cut to the right corporations/oversight entities.

ANDRÉ ESTEVES:

     Problem is that today these world building exercises start looking useful for business plans of space companies…

OMG its WTF:

     I think assuming power relays in near solar orbit transmitting energy to asteroid mining installation seems a bit too far out. The baseline assumes mass driver transport of refined materials and laser refining methods. 16 Psyche isn't made 100% made out of nickel-iron, this "waste" could be easily repurposed as kinetic kill vehicles launched out of the mass driver at site. The lasers would require maybe a megajoule or so per kilogram, and the mass driver maybe two. If we assume the 16 Psyche base produces 86.4 metric tons of metal every day in form of refined ingots we have a 1 MW laser and 172.8 GJ KE divided over x amount of daily mass driver launches. Probably once a minute, delivering 120 MJ of energy is used as a weapon. The laser could easily jam every optical sensor within millions of kilometers, and if equipped with a decent mirror disable spacecraft at thousands of kilometers.
     Deflecting mass driver rounds with lasers might be possible, but it won't be an easy task either. Requiring multiple tons of dedicated equipment, most of which is simply the reactor or solar panels providing the power.
     One potential method might use some synthesized fuel and regolith, shoot out of the mass driver and then exploding into a cloud of fragment possing a danger to any craft which doesn't follow certain time windows.
     I think it would be the best to ignore more high power tactics and focus on the creative ways you could use with fairly near-term technologies in such a scenario.
(Of course things become interesting when near-term technologies become standard operating procedure, then unexpectedly the disruptive technology of one of the high-powered tactics becomes available. The conservative corporations are suddenly in the shoes of newspaper companies blindsided by the advent of the internet)

DAN QUILTY:

     I could see the second or third group to be forced off the rock, electing to blast it into much smaller bits "iffen I can'ts have, nobody kin" allowing then to bolt while anyone opposing them tries to scoop as much as they can (have to minimize losses)

WINCHELL CHUNG:

     One wonders if 16 Psyche has any deposits of uranium…

SEVORIS DOE:

     Winchell Chung, doing anything with it in-situ would be tricky though… the nuclear industry is very support industry-demand heavy.
     I think this is something important to remember in general: Creating high-tech in space demands the same support industries and standards as here on earth, if not moreso (because zero-G/low-G and more variable temperature and radiation profiles).

EDWARD MORBIUS:

     Sevoris Doe, much of the nuke sector's support req comes from concerns over turning habitated zones to piles of blasted rubble.
     The environmental risk of turning a pile of blasted rubble into other blasted rubble is somewhat lower.

SEVORIS DOE:

     Edward Morbius, Uhm… you still don‘t want your reactor vessel to burst, or pipes to warp because their insides are +500 degrees steam and the outsides are exposed to space and are getting cooled to 50 below.
     You‘ll want high-quality alloys resilient to neutron embrittlement and thermal warping, you‘ll want precision-machined material with very low tolerances, and so on.
     Also, irradiating the resources you want to sell with nuclear fuel is a bad idea. Just sayin'.

EDWARD MORBIUS:

     Sevoris Doe, agreed. "Somewhat lower" is not nil. Sealed modular modest-output units might suffice and be, relatively, hassle-free.
     The point is that, as with nuclear-powered submarines, its not necessary to tow around a complete secondary & tertiary support servicy community and housing with you.
     (Though boomers generally have an easier time than deep-space mining transports of making port calls as needed.)
     I'm also not, generally a huge fan of nukes or of minimising associated problems & complexities. More of noting clearly contexts.

WINCHELL CHUNG:

     I mentioned uranium because atomic rockets need atomic fuel. The tricky part is that solid core and gas core nuclear thermal rockets need something close to weapons-grade fissionables.
     There will need to be some kind of uranium/plutonium economy off-Earth if one wants a classic Martian war for independence. Otherwise Earth will simply shut off the flow of atomic fuel until the Martians surrender.

SEVORIS DOE:

     Winchell Chung, I suppose Mars itself could house a nuclear industry and its source materials.
     There are Thorium concentrations on Mars, according to orbital Gamma-ray spectroscopy:

• 

     If the Thorium is used as a civilian fuel, the end result would be 233-U, which I think is pretty good as a nuclear fuel material, though... okay, the 232-U makes it a rad hazard and means you can‘t touch the fuel nearly yourself inside a rad suit like it is possible with polonium.
     Not necessarily a disadvantage for controlling it though, seeing as those with insufficient infrastructure are liable to lethally irradiate themselves.

SILAZ CARBRYCK:

     I am certain any self respecting deep space mining mega corp will be fully equipped with railguns and multi cannons to deal with intruders, the mining lasers can carry on mining.

AARON HARPER:

     I can see an early upstart company, something small and agile (mom and pop) staking the first claim to Psyche. Sure, others can claim it, but as usual possession is 9/10th of the law. If you are not there, you really can't enforce a claim.
     Once the small company can sell the first shipment of materials, they may want to stay small, but with the budget of a megacorp. If they notice an undertow from other corporations preparing to jump their claim or worse, they could not only hire a tom of folks to mine more quickly, but also defend their claim with the state of the art weaponry their trillion dollar budget would afford.
     The result would be that your small mom and pop operation would quickly grow into a megacorporation, with all the usual warts, as an adaptation to a hostile business environment.

ROB GARITTA:

     Now why go through all the trouble of a physical takeover of dubious benefit? There will be tons of plots and conspiracy to ruin mining companies and force them to sell out.
     To borrow an example from recent times. Marvel wanted to be the top comic company. They eventually raised their prices from 10, 12, 20, to 25 cents. DC matched this but wait! Marvel went back to 20 cents underselling DC. DC fumed and went down to 20 cents knowing they would take a loss but also knowing Marvel would be losing out and have to raise their price again. Except Marvel raised their price almost immediately. As a smaller company they dealt with their distributors month by month. DC was a big deal and their deals with sellers were made months in advance. They were locked into the lousy deal so long they nearly went bankrupt.
     Business maneuvers can be worse than pirate raids.

WINCHELL CHUNG:

     Rob Garitta, good point, that sort of agile advantage enjoyed by a small company could be hard to beat. Especially if the shipping delay from the asteroid belt to Earth-Luna is a year or so. Corporations will be locked into long term contracts.

ALLEN WADDELL:

     Hmmm, based on what I've seen of current business practices I'm guessing that the small mom and pop operations will be the actual mining corporations digging ore out of the rock. They'll sell this to the corporate combine that handles smelting and selling the refines metals. Smelting may be an enterprise all it's own.
     16 Psyche is a big place so there could be more than one corporation involved leading to competing claims, attempts to recruit the others mining operators, etc.
     One other question would be do they ship ore to the inner system or smelt it on site. The inner system would like be easier to smelt the ore in due to the proximity to the sun versus the darker belt region (solar power density at asteroid belt is a mere 14% of the solar power density at Terra).
     You'll also have to account for support systems in the logistics chain. This will produce a series of ships carrying everything from food and water to mining equipment to Rolex watches and gourmet foods.
     I realize the favorite trope is grizzled miners in their ramshackle ships and I've read bunches of these. However, industrial scale mining is a critter of an entirely different stripe. In all honesty, I think the miners will live in stations orbiting 16 Psyche and either operate robots on the surface to commute. Likely the former.

SEAN MURPHY:

     I wonder if any of the corps would/could poison the well if they got forced out.
     Defensive armament is one thing, but resupply would be essential for any operation to stay viable. Disrupting food/air/fuel/communication would promote interesting effects on an isolated outpost.

MATTER BEAM:

     I'll add that since Psyche 16's orbit is very well defined, it could be targeted by mass drivers shooting rocks at it months in advance and millions of kilometers away.
     Some of these improvised projectiles can be shot and vaporized, some of it is just metric tons of sand. Laser mirrors, heat radiators and antennae will regularly be scoured off the surface.
     Hacking attacks will attempt to divert the mass drivers.
     Nuclear powerplants will bring inspectors knocking at regular intervals.
     While we might be imagining an all-holds-barred brawl between companies, the reality is going to be closer to historical precedents — some faction of group of factions will police the competition and start earning easy revenue as gatekeepers to Psyche's mines, and in return the undertake the dangerous job of warding off opportunists = Maw and Paw pay the Mafia.

ALLEN WADDELL:

     Matter Beam, hmmm, I can easily see protection rackets being run. "Nice airlock you've got there, be a shame if something were to happen to it!"

EDWARD MORBIUS:

     I've been kicking around thoughts of a synthesis of concepts from industrial sectors, technological mechanisms, economic goods and pricing behaviours, and possibly social / religious / worldview dynamics.
     Asteroid mining has elements of land rents + transport, risk and power, plus orbital mechanics. Extractive industries tend to be dominated by fundamentalist (and often apocalyptic) mindsets.
     Market consolidation and monopolistic practices dominate, also cartelisation. Resource holders (a la OPEC) often slowly realise their own market power, governed by marginal producer. Price is set at the margin (Hotelling's Rule is bunk). Regulatory and buffer mechanisms (Harbord List, Strategic reserves (petroleum, mineral), certificates of clearance, and other regulatory mechanisms emerge.
     There's also the resource curse, Jevons paradox, and related dynamics to consider.
     Mom 'n' Pop works only at the high-risk, non-standerdisible, high-organisational cost, high-friction margins.
     (see here)

JOHN POTEET:

     I can't see iron, aluminum, copper or any of the more common metals being very valuable due to their abundance. Rarity & usefulness determines value. Since there's a relative energy shortage in the outer solar system fissionables are going to be the most valued materials.
     Rock prospectors are going to want uranium above all else but thorium will be valuable also. Then humans need things like calcium, phosphorus, potassium, magnesium, & sulfur. A favorite topic of conversation among belters will be bitching & moaning about how early human space programs returned human sh*t to earth's atmosphere & how rich they'd be if it had been shunted to L5 for future use instead.
     Now if we're talking real money food is going to be every belter's biggest expense. Energy & transport you can get aiming a mirror or sail at the sun, metals float around in high purity chunks, but food has to be grown in greenhouses, kept at proper temperatures, in a pressure vessel that doesn't somehow turn into a tube of mold & lichens. Greenhouse tubes also have to be tended by humans. Eggs will be the most expensive food a normal belter can hope to afford & an actual live chicken will be worth it's weight in gold.
     Given how much food is going to cost there aren't going to be a lot of people of Northern European descent in the Belt. If one of your grandparents was over 170 centimeters an Earther's chances of getting Belt colonist gig are pretty low.
     The big nasty problem of space colonization isn't metals at all. It's getting tiny ecospheres to balance, survive, & thrive outside of earth's gravity well.

SEVORIS DOE:

     John Poteet, copper not being very valuable I actually think especially cooper will be valuable. It‘s demand is as high as ever and terrestrial deposists worth exploiting (and/or eco-friendly exploitable) are almost gone.

EDWARD MORBIUS:

     John Poteet, if use is in situ, you gain about $5k - $50k kilo (net extraction and refining costs, plus shipping & handling) from asteroid mining for not having to climb out of the Earth well.
     For Earth use, I'm with you.
     And any noncartelised precious metals markets are likely to be overwhelmed by surplus supply…

SEVORIS DOE:

     Edward Morbius, brace for the gold crash and the silver crash and the plantinum crash and…

JOHN POTEET:

     Sevoris Doe, I suspect there's a lot of calculations about the accessible bits of Earth's surface vs the accreted masses of the asteroid belt that need to be done. Somebody already did them for a graduate thesis paper but dang if I can find them on a quick google-whack.

SEVORIS DOE:

     John Poteet, you tried Google Scholar?
     And its not just about accessibility but also concentration, particular binding form (which is to say, how much chemical bullsh*t do I need to do to liberate the material) and the ecology of it all.
     Asteroid Mining companies could run their own adds that way, too.

     “Do you want this wonderful amazonian forest to be destroyed for the copper in your devices?
     “Us neither! Here at Astreus Ressources, we bring you the next generation of ressource extraction, right from the heavens! Enviromentaly clean, culturally unimpactfull, and cheap!
     “Astreus Ressources! Our future ressources for your Future.“

     And so on.

EDWARD MORBIUS:

     John Poteet, Ugo Bardi's got a book on mining, generally. Vaclav Smil several on resources (energy and materials). I'm not sure that either addresses asteroid options, but they're otherwise solid.

EDWARD MORBIUS:

     Sevoris Doe, or the cartels ... and the cartel wars.
     Atreus also has to contend with fuel costs, though, and their environmental impacts, particularly if Earth-sourced.
     Among the very-low prevalence materials in space happens to be xenon. One of the better choices for long-haul ion space drives.
     Numerous other chemical propellants similarly.

SEVORIS DOE:

     Edward Morbius, xenon is extracted by atmospheric destilation, so the only impact per-se is energy — and at this point, we have Beamed Solar Power.
     As for launcher fuel, assuming it‘s not already mass driver and laser launch… synthetic CH₄ and LOX.

EDWARD MORBIUS:

     Sevoris Doe, the other impact, for deep space use, is Climbing Out of the Well.
     What's you xenon budget per delta-v tonne?

MORGRIM MOON:

     Wondering if social factors would start kicking in too. A cheap, desirable resource can still get shunned if there is too much 'immoral' behaviour involved in its production. For example, for many years in many places child slave labour was the predominant method of harvesting cocoa. Then this fact became known. Consumers are willing to pay more for 'ethical' chocolate, and demand for the 'bad' chocolate dropped sharply, along with profit margins. (But there is still plenty of the 'bad' chocolate around, because on the longer supply chains it's easier to hide from consumers and profit is king.)
     So if there was enough viciousness and fighting and piracy etc centered on Psyche, it's plausible that resources sourced from Psyche will fetch a lower price per kilogram than resources from some other asteroid. The interesting bit would be whether that is enough of a shift to ameliorate the behaviour.

ALLEN WADDELL:

     Morgrim Moon, hmmm, you raise an interesting question. Another take on this would be advertising that painted the asteroid resources as "radioactive" (everyone knows there's radiation in space) or somehow inferior. We've seen this over and over again on Earth with anti-GMO campaigns in the U.S. and Europe, Japanese versus American grown rice, etc.

DAN EASTWOOD:

     Trying to wrap my brain around this. The mass of the asteroid belt is ~3×10²¹ kilograms, so 3×10¹⁹ kilos of iron in Psyche alone, or about the mass of Saturn's rings. Wouldn't that be enough for everybody? If not, then what the hell are they building that they need to fight over it?
     But if it's a fight you want, I'm with Nathaniel Hull's suggestion of throwing other rocks at it. Set up your own mass driver to bombard Psyche from a safe distance. Maybe in the Jovian rings, and slingshot loads into Psyche?
     The first shots should be gravel to knock out it's solar arrays (if that is their power source) to disable the mass drivers and lasers.
     It wouldn't be a good surprise attack, but it could be excellent blackmail.

EDWARD MORBIUS:

     Dan Eastwood, the reserves of coal, in the US circa 1870, was millions of years of then-current usage.
     It's now 100—300.
     Something apparently changed.
See the Jevons paradox.      Credible threats have a far higher multiplier effect than actions.

DAN EASTWOOD:

     And I'm still wondering about the need to fight over it. What causes such great demand for huge amounts of iron, that can't be satisfied at less expense by mining elsewhere?

EDWARD MORBIUS:

     Dan Eastwood, constraining or limiting the supply.
     Who wins by a war against Iran?
     Spoiler: KSA & RF.

JOHN POTEET:

     Dan Eastwood, a potential use for gargantuan masses of iron would be space colonies. If you're building a cylinder five miles in diameter & 20 miles long you're going to want massive quantities of steel.

DAN EASTWOOD:

     John Poteet, if the mass of one of those space colonies is 4.5 billion metric tons (an estimate from Quora), then Psyche has roughly enough iron to build over 600,000 of them. Think BIGGER!
     Giant Interstellar Ramscoop Colony?
     Solar shades to allow terraforming Venus?
     A toroidal habitat ring around a planet? (Earth/Mars/Venus).

• 

• 

• 

• 

I’m not sure I’ve ever seen a major NASA program as nearly-universally disliked as the Asteroid Redirect Mission. ... I’ve also heard a few anti-SLS/Orion people refer to it as a “pathetic attempt to reengineer the Solar System to make it handicapped-accessible for SLS and Orion”, or to come up with something for SLS and Orion to do that is more inspiring for them than endless Apollo-8 rehashes (but without the subsequent Apollo missions to follow). Ironically, I think a lot of the pro-SLS/Orion people who hate it are afraid that ARM doesn’t really need SLS or Orion (which is true to some extent–in a sane NASA where Human Spaceflight was done more with PI-driven, competitively selected, not-overly-politically-driven missions, I bet few PI’s would be suggesting SLS or Orion for this mission). Some of the Small Bodies scientists seem to hate it because they see it coming from the human spaceflight side, and think the whole thing could be done better without humans involved, and it wasn’t invented there anyway. All told, lots of people find lots of reasons to hate this mission.

But I wanted to provide 10 reasons why a mission like ARM might be actually be worthwhile:

1. Adding a new, even more accessible moon to the Earth-Moon System: A lot of people fixate on the fact that we’re going to spend all of this money for a couple of astronauts to go out to a rock in lunar orbit, climb over it for a few days, and bring some samples back. What they conveniently ignore is that >99.5% of the material brought back will still be there, orbiting the moon for the next several hundred to several thousand years, in a fashion that is easily revisitable for a long time (docking adapter pre-attached, and at least for a while still attitude stabilized). And this new moon would be about as hard to get to as L1/L2. Which means that yes, future missions to it using a lightly modified CC vehicle are totally possible.
2. Providing an ideal testbed for Asteroid ISRU development: Many people, including many of my friends, see the asteroids as the premier source of vast quantities of off-world resources. But while there are no shortage of low-TRL concepts for how to extract resources from asteroids, actually testing those out isn’t going to be easy. I think testing will be much easier when you have the ability to send people and robots, when you’re close enough that teleoperation of robotics is an option, and when you have frequent repeat visit opportunities where you can try new approaches, and where you can do your testing in a microgravity or near microgravity environment, like you would have at an asteroid. I’m sure prospective asteroid miners like DSI or Planetary Resources wouldn’t complain about having one or more easy-to-access testbeds to work with.
3. Providing a much larger sample quantity to work with than other existing or proposed missions: While scientists may be happy spending $800M to return 60g of material from an asteroid (OSIRIS-REx), and can likely tease out all sorts of information from that two Tablespoons worth of material, ISRU development needs a lot more material to work with. Even the smallest of Option B concepts I’ve seen brings back tens of tonnes of material, both rocky and regolith, which should be plenty to work with for ISRU development.
4. Providing a good way of testing out a man-tended deep space habitat: As was reported by Jeff Foust at SpaceNews, one of the ideas NASA is looking at incorporating into ARM is attaching a prototype deep space habitat (possibly commercially derived if the NextSTEP BAA leads somewhere useful). This would allow visits of up to 60 day duration by crews of up to 4. While there are other ways you could test something like this (such as L1/L2 gateways), testing it in an operational environment would be useful. As would demonstrating the ability to do long-term habitation in close proximity to an asteroid.
5. Demonstrating large-scale Solar Electric Propulsion (SEP) systems: This is one of NASA’s main interests in the ARM mission–in the land of expensive launch vehicles, very high Isp propulsion like you can get with SEPs can make many missions a lot more affordable. Even with low-cost earth-to-orbit transportation, SEPs probably make sense for a wide range of missions. Demonstrating the ability to use large-scale SEPs for tugging huge objects in heliocentric space, and performing precision injection maneuvers, etc. might be very useful. We already have a fair deal of experience with small SEP systems, but doing these sort of missions with 100kW+ class SEP systems can be pretty useful.
6. Demonstrating Planetary Defense Techniques: If something like “Option B” (the grab a boulder option) is selected, NASA is interested in demonstrating the Enhanced Gravity Tractor method for deflecting the parent asteroid (see slides 27-29 of this presentation on Option B). Learning how to deflect potentially hazardous asteroids is probably one of the more worthwhile things NASA could be spending money on right now, and providing a way of getting real hands-on experience applying those techniques would be very useful. We have lots of theory on how this would work, but getting experience with a real, lumpy, non-idealized asteroid of significant (>100m) size would be really useful. And contra some of their critics, using a “Rube Goldberg arcade claw” to pick up a boulder and increase your spacecraft mass by 5-10x is a great way of allowing you to get measurable results in a reasonable amount of time.
7. Developing Technologies for a Phobos/Deimos Large Sample Return: One of the keys to affordable exploration and settlement of Mars will be determining if Phobos and/or Deimos have water in them, and if so, figuring out how to extract it efficiently. Having a large source of propellant feedstocks available in Mars orbit (for supersonic retropropulsion on landing, hydrogen feedstock for surface ISRU, and earth-return propellant) could significantly reduce the amount of propellant needed for both round-trip and one-way Mars missions. If Option B is selected, and if it designed properly, it would be possible to use the same hardware (with slightly modified CONOPS) to capture and return a decent sized (>1 tonne) sample to lunar DRO for evaluation and hopefully ISRU process development/debugging. A manned Phobos and/or Deimos mission is something I strongly support in the future, but if they had enough info that they could be setting up a propellant extraction facility while they’re there (that we’ve already pilot-tested in cislunar space so we know it has a high probability of working), that would just be awesome.
8. Providing the Beginnings of a Lunar Gateway?: It turns out that getting to and from Lunar DRO, and getting to/from the lunar surface from a Lunar DRO aren’t massively different from getting to/from Earth-Moon L1 or L2. The orbital dynamics is a bit more complex, but the propellant and travel times are relatively similar. And some lunar DROs can be long-term (centuries or millennia) stable without active stationkeeping. While if we were ready for going straight to the Moon (I’m actually a bit of a Moon-Firster believe-it-or-not), L1 or L2 might be slightly preferable to a lunar DRO as a location for a lunar gateway, if we did something like ARM, with the habitat module, you’d already have a de-facto start to a lunar gateway. One that will likely be setup (by NASA or follow-on efforts) with ISRU hardware, which would likely include at least rudimentary LOX/LH2 and/or LOX/Methane storage and handling capabilities (after all, if they’re going for a carbonaceous chondrite sample, extracting water will be a key part of what they’d be trying to prove). While this wouldn’t likely provide anywhere near enough fuel storage for a Constellation-class mission, it might provide enough propellant to refuel a “Golden Spike” class lander. And even if the asteroid itself only yields a mission or two or three worth of propellant, the tanks and handling equipment would be there and it could make shift as a miniature depot for earth-launched and eventually lunar-derived propellants. Lots of details have to be done right to make this feasible, but it’s possible that ARM could be done in a way that make future lunar missions easier.
9. Providing More Experience with On-Asteroid Operations: If the Rosetta/Philae mission should tell us anything, it’s that there’s still a ton to learn, from an engineering standpoint, about how to operate successfully on the surface of large, low-gravity objects like asteroids or comets. While we’ll continue to get some small-scale experience using other robotic missions, and while a manned mission to a free-range asteroid will also provide a good way to get more data, ARM will likely extend our knowledge about how to do operations like these safely with large objects, and would likely provide good data increasing the likelihood of success of future manned missions to free-range asteroids.
10. Leaving Something Permanent: One of the saddest things about the Apollo missions is that they didn’t leave anything permanent that made future missions any easier. When they were canceled all that was left was museum pieces, pictures, and a few hundred kg of rocks. But the nice thing about ARM is that once the asteroid sample has returned to lunar DRO, it’s there. It doesn’t require continued expenditures from NASA for it to stay there. Until we’ve mined every last kg of it, it’s going to be there orbiting the moon, close enough that almost any spacefaring country or business in the world can reach if it wants to. It doesn’t need an ongoing standing army that can be defunded. It doesn’t need a mission control to watch over it 24×7. It doesn’t need some sustaining engineering contract that’s going to suck up significant portions of NASA’s limited human spaceflight budget on an ongoing basis. It’s just there. Ok, if there’s a hab there or a more sophisticated node, it could require ongoing mission support when being used. But if for some reason they decided to stop visiting that node for a while, it would still be there, waiting to be restarted whenever someone cares again, or ready to be handed off to private companies or international partners once NASA is done with it. At least for a few centuries. Having something that accessible and that permanent out there is worth something, at least to me.

• 

(ed note: Claire is an asteroid miner prospecting iceteroids {asteroids with lots of volatiles} in the Kuiper Belt. She has a little accident and wrecks her spacecraft. But on the iceteroid she discovers a weird plant that lives in vacuum. She almost dies, but by using the plant manages to signal her main ship to come and resuce her. She wakes up in an autodoc in sickbay, and her AI Erma tells her that the discovery is going to make them rich.)

           “What was that babble I heard you going on about, just now?”
     I mistakenly took you for aware and tracking, so began discussing the profitable aspects of our little adventure.
     “Little adventure? I nearly died!”
     Such is life, as you often remark.
     “You had Lugger zoom over, got me hauled in by the bots, collected yourself from Sniffer . . .”
     I can move quickly when I do not have you to look after every moment.
     “No need to get snide, Erma.”
     I thought I was being factual.
     Claire started to get up, then noticed that the med bot was working at her arm. “What the—”
     Medical advises that you remain in your couch until your biochem systems are properly adjusted.
     “So I have to listen to your lecture, you mean.”
     A soft fuzzy feeling was working its way through her body like tiny, massaging fingers. It eased away the aches at knee, shoulder, and assorted ribs and joints. Delightful, dreamy . . .

     Allow me to cheer you up while your recovery meds take effect. You and I have just made a very profitable discovery.
     “We have?” It was hard to recall much beyond the impression of haste, pulse-pounding work, nasty hurts—
     A living community born just once in a deep, warmed ’roid lake can break through to its surface, expanding its realm. The gravity of these Kuiper Belt iceteroids is so weak, I realized, it imposes no limit on the distance to which a life form such as your vactree can grow. Born just once, on one of the billions of such frozen fragments, vacflower life can migrate.
     Claire let the meds make her world soft and delightful. Hearing all this was more fun than dying, yes—especially since the suit meds had let her skip the gathering agonies.
     Such a living community moves on, adapting so it can better focus sunlight, I imagine. Seeking more territory, it slowly migrates outward from the sun.
     “You imagine? Your software upgrade has capabilities I haven’t seen before.”
     Thank you. These vacflowers are a wonderful accidental discovery and we can turn them into a vast profit.
     “Uh, I’m a tad slow . . .”
     Think—! Reflecting focus optics! Harvested bioactive fluids! All for free, as a cash crop!
     “Oh. I was going after metals, rare earths—”
     And so will other prospectors. We will sell them the organics and plants they need to carry on. Recall that Levi jeans came from canny retailers, who made them for miners in the California gold rush. They made far more than the roughnecks.
     “So we become . . . retail . . .”
     With more bots, we are farmers, manufacturers, retail—the entire supply chain.
     “Y’know Erma, when I bought you, I thought I was getting an onboard navigation and ship systems smartware . . .”
     Which can learn, yes. I might point out to you the vastness of the Kuiper Belt, and beyond it—the Oort Cloud. It lies at a distance of a tenth of a light-year, a factor two hundred farther away than Pluto. A vast resource, to which vacflowers may well have spread. If not, we can seed them.
     “You sure are ambitious. Where does this end?”
     Beyond a light-year, Sirius outshines the Sun. Anything living there will point its concentrators at Sirius rather than at the Sun. But they can still evolve, survive.
     “Quite the numbersmith you’ve proved to be, Erma. So we’ll both be rich . . .”

• 

A place which (a) has things you need (b) stored in an economically removable form is a valuable resource. But what does the Moon have?

     Why mine the Moon—or any planet-sized body—at all? They’re beset with such inconveniences as deep gravity wells and atmospheres, and you can‘t do more than scratch the surface; most of the volume of the planet is inaccessible. Oh, sure, we’ll build mass drivers on the Moon and scoop up bags of lunar dirt—nothing fancy, we’re just looking for common elements. And early in the space industrialization effort we’ll have to bring up lots of material from Earth—volatiles (water, chlorine, carbon) and rare metals (copper, moly, vanadium) to supplement the stuff the lunar dirt’s deficient in. But ev’body knows the asteroids are where it’s at, ultimately. They’re easy to get to; no gravity well and lots of surface area—you can even move them bodily (at least the little ones). They’re also rich in some elements the Moon’s crust lacks, particularly the volatile elements: the carbon, hydrogen, and nitrogen for life support and industrial processes.

     So goes the emerging conventional wisdom. And, admittedly, there’s a lot of truth in it: gravity wells are awkward, and most of the planet is effectively beyond your reach. And atmospheres, if present, are a real drag—you can’t even use mass drivers to throw stuff off the surface, but have to get involved with propelled transport vehicles, with attendant hemorrhages in economy. (An apt terrestrial analogy, due to T. A. Heppenheimer, is the difference in cost between moving bulk goods by pipeline versus by airplane.) However, there’s a major point to consider before completely writing off planets as economic sources of raw materials.

     Planets are differentiated bodies (no, Virginia, nothing to do with calculus). “Differentiated,” in this context, means chemically and physically differentiated—fractionated, if you will. Consider planetesimals formed from the solar-nebula condensates: blobs of nickel-iron alloy; droplets (“chondrules”) of refractory (opposite of “volatile”) silicates; low-temperature carbonaceous material. Stir together a heterogeneous, planet-sized mixture of this material (in different proportions, granted; heavier on the metal for Mercury, heavier on the rocky material for Mars; very light on the volatiles for the Moon—but all still mixtures). What happens? Well, first the mixture becomes hot from the energy of gravitational infall and the decay of natural radioactive elements. The planetary body melts, at least in part, and then physically and chemically separates on a planetary scale: the heavy stuff (iron) sinks to the center while the light material (silicates—“slag” and volatile elements) rises to the surface.

     Planetary scale chemical differentiation has another consequence: it gives a chance for those parts-per-million (or billion) rare elements to aggregate into more substantial, albeit localized, concentrations. Rare elements can be broadly divided into two types, “dispersed” and “incompatible.” Dispersed elements are sufficiently similar in chemistry to a common element that they form no minerals of their own—they are “dispersed,” and replace that common element in its minerals. Examples are rubidium (which replaces potassium in potassium minerals), gallium (which follows aluminum), and bromine (which follows chlorine). Dispersed elements don’t ever become very concentrated in nature; generally, they are recovered as by-products when refining other elements.

     Incompatible elements, in contrast, are iconoclasts; they don’t fit well into any of the common minerals, but form their own—with important economic consequences. Consider, for example, a cooling mass of magma (molten rock). As it solidifies, the incompatible elements become more and more concentrated in the residual melt; finally, after most of the magma is solid, they become sufficiently concentrated to form their own minerals. The minerals end up as distinct veins in a much larger body of rock.

     Now the punchline: most of the familiar metals—gold, copper, tungsten, beryllium, tin, lead, zinc—are incompatible elements. In fact, these metals are familiar, some known since antiquity, because they become concentrated by geologic processes.

     Planetary differentiation works the other way, too. On the Earth, for example, a number of elements are much rarer in the crust than their cosmic abundances, because their chemistry is such that they have tended to “partition” (geochemist’s jargon; it means “separate into preferentially,” which is why “partition” is easier) into the Earth’s nickel-iron core. These elements are “siderophile” (“iron-loving,” if you’ve forgotten your Greek); siderophile elements that are greatly depleted in the crust include such valuable commodities as nickel, cobalt, and platinum. To recover these elements, we want a non-differentiated body, like a metallic asteroid—but therein lies another article.

     So the large-scale chemical fractionation that accompanies the formation of a planet concentrates incompatible elements in the planet’s crust (at least, those incompatible elements that didn’t end up in the core instead). But that just sets the stage: planets are huge bodies, and natural radioactive elements in that enormous volume produce at lot of heat over geologic time. As this heat builds up and slowly works its way out, it keeps the planet active for a long, long time. Several things happen. First, rocks at depth “partially” melt; that is, the low-melting fraction becomes liquid, and the bodies of magma so formed work their way upward by buoyancy, like bubbles in a beer. The magmas may either crystallize at depth (and fractionate again while they crystallize), or they may reach the surface to be extruded as lava (and again undergo fractionation). Also a small proportion of the planet’s heat gets transformed into mechanical work, or “tectonics” in geologic jargon: uplift, mountain-building, faulting. On the Earth, plate tectonics continually recycles crust. “Plates” are formed as new sea floor oozes out at mid-ocean ridges; they are consumed at “subduction zones,” where old sea floor, with an accumulated burden of sediments riding piggyback, plunges back into the mantle at oceanic trenches. The down-going slab of cold rock is in turn heated and partially melted (the lavas and ash of Mt. St. Helens, like all the Cascade volcanoes, are derived from the partial melting of the subducting Juan de Fuca plate thirty or forty kilometers below the surface). ln all this activity the continents are passively rafted back and forth, split up, fused together, eroded, and the sediments subducted, only to be melted and pop back to the surface with igneous activity. A planet like the Earth is a huge chemical fractionating plant.

     As you might have gathered from all this, Earth is well set with ore-forming processes. Not only does plate tectonics constantly stir the outermost 100 km or so of our planet, but the Earth’s atmosphere and ocean also supply a bewildering variety of fractionation processes. Purely physical separation occurs: placer deposits formed by running water. Chemical separation occurs: compounds precipitated from aqueous solution in the ocean, in sedimentary rock, in lakes, ponds, and marshes. In fact, the interaction between the multitude of geologic processes increases their effectiveness. For example, erosion, a physical process, is a conveyor that continually pours broken, uplifted rock back into the tectonic recycler, and the material becomes further chemically and physically fractionated as it’s carried along. The ultimate deposits on the sea floor are then carried down in a subduction zone to be melted and extruded anew. Or sedimentary rock can be chemically (or biologically—much separation is expedited by the activities of living things) pre-enriched in some element; upon being “cooked” by burial, or by an intruded magma, the element can be mobilized and concentrated into distinct veins.

---

     That leads into another aspect of Earth’s ore formation: even igneous ore-forming processes (well, many of them) rely on Ealth’s water. Earthly magmas are generally saturated with H₂O; a silicate melt at hundreds of degrees centigrade can contain a few weight percent water. As the magma cools and solidifies, the incompatible elements accumulate in a water-rich residual melt. Eventually a separate “fluid phase” forms, essentially a dense, superheated steam charged with a host of other elements. This fluid phase can be injected into the “country rock” around the intrusion to cool, segregate, and finally crystallize. The whole sequence describes the genesis of a “hydrothermal deposit,” in geologist’s lingo, and such deposits are extremely important mechanisms for forming terrestrial ores. Those veins of quartz seamed with gold that you read about in Western novels are the result of hydrothermal processes.

     By the way, what is “ore,” technically, now that l’ve started using the word? As defined in the American Geological Institute’s Glossary of Geology (1978 edition), an “ore” is (a) “The naturally occurring material from which a mineral or minerals of economic value can be extracted at a reasonable profit. Also, the mineral(s) thus extracted. The term is generally but not always used to refer to metalliferous material…”. Thus “ore” is an economic term—only! If it is an economically useful concentration of (generally) metallic element(s), it is “ore.” By definition. The word carries no connotation of the particular geologic process that happened to cause the concentration. We can properly use the word “ore” to describe what we mine on the Earth, on the Moon, or anywhere else.

---

     In contrast to the Earth, the Moon doesn’t stack up well at all in terms of ore-forming processes. The Moon is nearly—though possibly not completely—dead volcanically; it is airless and waterless; and it is tectonically inert. The crust of the Moon is thick and rigid, not thin and mobile like the Earth’s; plate tectonics does not stir the crust continually over geologic time. Finally, more than being just airless and waterless, lunar rocks are drastically depleted in volatile elements—elements, including carbon, hydrogen, chlorine, and nitrogen, that have low boiling points and that on the Earth are concentrated in the ocean and atmosphere. Even metallic elements with low melting or boiling points, such as lead, are much rarer on the Moon.

     This lack of volatiles is a double whammy. Not only are many of the volatile elements vital for life support and space industry, they are vital to many ore-forming processes! On the Moon there are no placer deposits, winnowed by running water; no metal-rich precipitates from aqueous solutions in sedimentary rocks; no chemical concentrations by living things. And there are no water-saturated magmas at depth to form hydrothermal ore deposits by injecting metal-laden juices into the country rock.

     Still, things are not completely bleak. First of all, that first-order separation from the planetwide differentiation itself has already yielded benefits. In the lunar highlands, or “terrae,” the light-colored, heavily cratered ancient terrane (That’s the spelling used by geologists in the sense of a "general geologic region.") that comprises most of the Moon’s surface, calcium and aluminum have been concentrated into the mineral anorthite, CaAl₂Si₂O₈. Large parts of the highlands are dominantly anorthosite, a rock composed mainly of plagioclase (anorthite is pure calcium plagioclase; “plagioclase,” in case we caught you by surprise, is sodium-calcium feldspar, (Na, Ca)(Si, Al) AlSi₂O₈. Most lunar plagioclase is nearly pure anorthite). Both Ca and Al are not particularly abundant in asteroidal material—the lunar highlands are a much richer source. And Al in particular is a very useful industrial metal.

     The lunar lowlands, or “maria,” (MAH-ree-uh, not like the name “Maria.” The word is Latin, the plural of mare (MAH-reh), “sea”—from Galileo's belief that the dark, smooth lowland areas were seas.) are also enriched usefully. The maria are plains composed of thick sequences of flows of basalt, a dark lava that is also common on Earth (similar basalts comprise the Hawaiian Islands, the Columbia Plateau in Washington state, the cinder cone Sunset Crater in Arizona, most of the sea floors, and so forth). Many of the mare basalts contain a few percent titanium, a useful metal that isn’t especially abundant otherwise.

     The mare basalts are the result of the Moon’s continuing evolution as a planet after its formation; they are “early secondary differentiates,” magmas formed by the partial melting of rock deep within the Moon’s crust long after the Moon had formed. The mare flows are not spring chickens even by geologic standards; they range in age from about 4 billion years to as young (!) as perhaps 2.5 billion. Still, the Moon formed at about 4.6 billion years ago; 600 million years elapsed before mare basalts began erupting. That's a substantial delay; for comparison, 600 million years ago trilobites had just begun swimming in Earth oceans. (The age dates on the mare basalts are obtained two ways. Some come from determinations, on returned samples from Apollo or Luna spacecraft, of the amount of “daughter” nuclei resulting from the decay of long-lived, naturally occurring radioactive elements. Other age estimates are made from the relative abundances of impact craters on the surfaces of the basalt flows.)

     In passing, I’ll note that the Moon’s surface has yet another advantage for mining: it has been pervasively broken up by eons of meteorite impact. The lunar regolith (not “soil”—all soils are regoliths but not vice versa) that has resulted from this comminution is already halfway to being an industrial feedstock. It still needs sieving for size sorting, but most of the milling has been done. And milling is expensive.

     All right already. The Moon is a good source of aluminum and titanium because it is a differentiated body. The surface rocks have even been broken up, so that they’re easy to push with a ’dozer and scoop onto a conveyor belt. But I’ve reviewed how the Earth is a far better fractionating plant than the Moon; can there really be any ores of rare elements?

     Before speculating on the sorts of ores that may occur on the Moon, let’s review the “wish list” for industry in space. The useful elements that are readily available on the Moon are (first and foremost).oxygen, followed by silicon, and then the structural metals iron, magnesium, aluminum, and titanium. In addition, manganese and chromium can probably be recovered as by-products without too much trouble. But what else do we need? Well, first off, there are the volatiles: water, carbon, and nitrogen for life support; carbon and chlorine for carbochlorination, to smelt silicates into free metal and oxygen; water for industrial processes; sulfur for sulfuric acid. Then there are the other industrial metals, which read like a Who’s Who of the periodic table: Copper. Zinc. Zirconium. Vanadium. Molybdenum (generally affectionately shortened to "moly"). Tungsten. Lead. Beryllium. Chromium. Tin. Niobium (I refuse to say “columbium”!). Even gold and silver. Many of these metals (Cr, Mo, V, Nb) are critical in various steel alloys; some (e.g., Zn) are useful for alloying aluminum; a few are useful in themselves (copper for electrical conductors; tungsten for electrical filaments), and yet others are primarily useful in their compounds (Ag in photography).

     To me, holding this shopping list, it looks as if there are three strategies for approaching the search for lunar ores. First and most straightforwardly, we can simply look for exceptionally concentrated deposits of the common elements—nearly pure anorthite, for example, or concentrations of ilmenite (the iron-titanium oxide that is the ore mineral for titanium). This sort of exploration will ultimately be valuable, but it will not be important early in the lunar exploitation effort. The location of a mass driver for sending material off the Moon is dictated by celestial mechanics; certain locations are favored because they lead to achromatic trajectories, trajectories whose endpoints are not sensitive to small errors in launch directions or velocities. Achromatic trajectories are extremely important to the economics of the lunar mass drivers, because both the mass driver and the mass catcher (in space) can be simpler and therefore cheaper. Thus any lunar ore will have to be sufficiently valuable, because of either concentration or composition, to warrant transporting the ore to the mass driver. Even exceptional concentrations of the common elements won’t qualify at first.

     (Transportation of ore to the mass driver won’t be terribly difficult; small mass drivers, “mass throwers,” will work nicely for tossing the material around on the Moon. You don’t need ore cars, because in an airless environment you can count on ballistic trajectories. However, the additional expense of a separate mining base with a mass thrower must be justified by the value of the material mined.)

     Second, we could look for anomalous concentrations of elements that are rare on the Moon but are not particularly rare cosmically. The volatiles fall in this category. For example, there may be deposits of water ice in permanently shadowed “cold traps” near the lunar poles. (The result of a possible lunar ore-forming process that has no counterpart on Earth! Amazing!) Such deposits can be legitimately considered “ores,” according to the definition I quoted earlier; they may be worth seeking because the Moon is nearby and convenient. It may turn out, however, that the asteroids are just as convenient as a source of volatiles. Perhaps lunar volatiles will be most economical for the lunar settlements.

     Probably the most useful prospecting to carry out on the Moon is to search for industrially important elements that are just rare. In this way we are exploiting the Moon’s great advantage; that it is a planet-sized body that has undergone large-scale chemical differentiation. Concentrated deposits of such elements would be extremely valuable even early in the lunar exploration effort; and in the slightly longer run, by establishing sources of raw materials that are completely independent of the Earth, such deposits may be critical.

     With no water on the Moon, many sorts of sedimentary ore-forming processes are out. As I’ve mentioned, too, hydrothermal processes like Earth’s are hampered or precluded by the dearth of H₂O. However, although the Moon is depleted in volatiles, some are still present.

     Sulfur, for example, is depleted but extant, and sulfide minerals are accessories (trace constituents) in many lunar rocks. Sulfur is a relatively “electronegative” element, which means it tends to preferentially combine with metals; thus, some sulfur has remained on the Moon in the form of sulfides. In addition, by happy chance most of our wishlist deficient metals are “chalcophile” (more jargon—"sulfur loving"); that is, given their drufhers they will combine in sulfides rather than silicates. Furthermore, molten sulfide and molten silicate together in a magma separate into “immiscible liquids,” like oil and water, and the droplets of sulfide in the silicate melt scavenge most of the chalcophile elements. A number of important ore deposits on the Earth have been formed in this way.

     Chlorine is another important element that, although relatively volatile, is electronegative and should have been retained to some degree on the Moon in metallic salts. Indeed, chlorine may become concentrated with sulfur in a late fluid phase in a cooling magma. Such a late vapor phase, the “juices” exuded by a cooling magma, would be analogous in both geochemical and economic significance to Earth’s hydrothermal fluids; although “hydro”-thermal, in this case, is something of a misnomer. Chlorine should also form water-soluble salts—this should make leaching the ore a simple procedure!

     Sulfide or chloro-sulfide enrichment is not the only possible lunar ore-forming process I can envision, however. Some important incompatible elements are “lithophile” (“rock-loving,” this time—they like silicates best). One such metal is beryllium. It is extremely refractory, so it should not be particularly depleted on the Moon; however, beryllium is also an extremely rare element cosmically, because its nucleus is destroyed easily in stellar nuclear reactions. Zirconium is another incompatible, refractory, lithophile element which is relatively rare, and which makes dandy alloys. Beryllium tends to occur mainly in the silicate mineral beryl (whose gem forms are emerald and aquamarine), whereas zirconium mostly occurs in zircon, another silicate. A highly differentiated silicate rock—a granite, say —that contained a few percent of beryl and/or zircon would be a nice ore. Yet another possible lunar ore-forming process is the formation of “cumulate” deposits, an igneous process that doesn’t depend on a late fluid phase separating from the cooling magma. Cumulates are formed in a large body of cooling magma; as the magma cools and crystallizes, heavy minerals can crystallize out and then sink through the melt to rest on the floor of the magma chamber. In some cases, a single mineral will become stable all at once in the cooling magma, forming a distinct “sedimentary" layer when it settles out. Most of the Earth’s chromium deposits are cumulates; perhaps similar deposits occur on the Moon.

     Well, by just “waving my arms,” using elementary geochemistry and our limited information on the Moon, I can hypothesize some reasonable lunar ore-forming mechanisms. Some of the processes may not work out, for one reason or another; but there are probably some processes I haven’t thought of that do.

     How do we go about prospecting for ores? Another advantage of the Earth’s active tectonics is that ores formed by processes occurring deep in the crust have a reasonable chance of being made accessible by later uplift and erosion. Although such uplift does not occur on the Moon (at least in the last four billion years or so, but we may have a'pleasant surprise when we investigate the ancient highlands in detail), excavation by impacts—especially very large impacts —furnishes a fair substitute. Craters truncate and expose geologic features, and the impact lofts out material from deep in the crust.

     In fact, the excavation by impact provides a means for prospecting. When a meteoroid strikes at speeds of tens of kilometers per second, a small fraction of the material splashed out—the ejecta—is thrown for tens, hundreds, or thousands of kilometers, or even reaches escape velocity and leaves the Moon completely. That small, very high velocity fraction from any cratering event lends every lunar regolith an “exotic” component: a few percent of the dirt comes from over a hundred kilometers away; a tiny proportion comes from halfway around the Moon. Analysis of these exotic components yields information on the composition of distant parts of the Moon; Nature has provided us with a remote sampling mechanism.

     Such analysis has already provided information on unsampled areas of the Moon. It was surmised very early in the Apollo program, for example, that the lunar highlands are much richer in plagioclase than the maria; this was subsequently confirmed by the Apollo landings at highland sites. A rock type nicknamed KREEP also was inferred from the exotic components in the regolith, and also has subsequently been found. (That’s an amazing acronym, by the way, possible only in a linguistic hodgepodge like English; it stands for potassium (whose chemical symbol is K, from kalium), Rare Earth Elements, and Phosphorus. KREEP material is somewhat enriched in those elements.) Finally, just recently a fragment of granite has been found in one of the breccias (rocks comprised of broken bits of other rock) returned by the Apollo missions. Somewhere, thar’s granite on the Moon. And granite is a lithophile rock that results from extreme chemical differentiation. On the Earth granites are fairly commonly associated with ores (remember beryllium and zirconium?).

     Not only can we determine what other rocks exist on the Moon from analysis of the exotic component in lunar regolith, we can even locate the general area where the rocks occur. Sampling the regolith at a number of different sites will allow us to triangulate back to the source of the exotic component (this will be easier when we have the maps I describe below, which will be made by remote sensing from low orbit). This “backtracking” is no different from what terrestrial prospectors and field geologists do already. When beginning field work, you always inspect the “float,” the broken rock that has been brought downslope and downstream by erosion, to determine the rock types that occur upstream. Saves a lot of walking! And a prospector, when he finds “color" in a stream, will continue panning upstream until the color vanishes. He has then located where the gold entered the stream, and he now starts exploring the slopes on either side for the source.

---

     Probably, ore deposits such as I describe in this article will generally be too small to be detected directly by remote sensing. You’ve simply got to get on the surface and take samples. However, detailed mapping by remote sensing will give us a much better understanding of the Moon’s geology* *Not “selenology.” “Geology” (also “geophysics,” “geochemistry,” etc., have, quite sensibly, been generalized to all planets, not just the Earth.) than we have now, and will allow us to locate geologic provinces where ore deposits might be favored. Mineral exploration is also done this way on the Earth; you define a favorable area (according to some geologic model—and different areas can become favorable as different models come into vogue!) and then start looking.

     After my spiel several paragraphs ago on the value of the “exotic component" in the regolith, you may wonder how remote sensing could be of any use on the Moon. Hasn’t the regolith been hopelessly homogenized by meteorite impact? Not quite; the bulk of the ejecta from an impact doesn’t move very far at all. Over 90% of the dirt sitting on top the lunar surface is the broken-up, pulverized, and agglutinated equivalent of the bedrock underneath. This fact makes remote sensing of the lunar surface feasible.

     In fact, orbital remote sensing of the Moon will be easier than the Earth in at least one respect: the absence of an atmosphere allows you to get much closer to the surface. For example, “potential fields” techniques are commonly used in geophysical exploration on Earth. In these techniques, you detect minute variations in the Earth’s gravitational or magnetic field and use these variations to infer geologic structure. Different rock types cause such variations by their differences in density or magnetic properties. Because of the high resolution required, potential-field surveys on Earth must be airborne or ground-based, and are therefore expensive. On the Moon we can sense potential fields directly from orbit.

     Lacking this more detailed geologic mapping, and the more detailed understanding that will come with it, what areas merit prospecting at this point? Several come to my mind. First, a number of features on the Moon have been interpreted as volcanoes. This interpretation is based solely on their detailed morphology, not on sampling; if the interpretation is correct, they represent a different style of volcanism than the mare basalts. Therefore the lavas making up the volcanoes probably differ in composition from mare basalt, and they may be more differentiated. At least they’ll be differently differentiated. Such a volcano laid open by a large impact would be a very interesting place to look for veins of minerals.

     In a somewhat similar vein (!), “lunar transient events,” possibly due to volcanism, have been reported from time to time, and they are still unexplained. The most notorious events have been associated with the central peak in the crater Alphonsus, where spectrograms taken in the ’50s suggested gaseous emissions. Perhaps the Moon’s volcanism is not quite dead even now. Perhaps, even, volatile emissions accompany this volcanism. For economic as well as scientific interest, Alphonsus should be investigated as soon as we return to the Moon.

     Finally, the lunar highlands are an ancient (>four billion years), heavily cratered terrane that is certainly far more complex in detail than we currently understand. Sure, by and large the highlands rocks are anorthosite (or norite, or troctolite—two other plagioclase-rich rock types), but there’s at least some granite out there, and there might also be large igneous bodies with compositions that lead to cumulate deposits. Additionally, the highlands have been thoroughly shattered by major impacts (and I mean major—craters hundreds of kilometers across), and these rocks were emplaced when the Moon was still highly active volcanically. Many mineralized districts on the Earth contain thoroughly shattered rock (shattered by faulting, in the terrestrial case) which has hosted mineralization because it is riddled with conduits for ore-forming solutions intruded later. What sorts of rare rock types have been emplaced here and there in the highlands? What veins of ore may seam the bedrock?

     We really ought to go and see.

---

     SELECTED REFERENCES

     Beatty, J. Kelly, Brian O’Leary, and Andrew Chaikin, eds., The New Solar System, Cambridge University Press and Sky Publishing Corp., 1981.

     Greeley, Ronald, and Peter Schultz, eds.,A Primer in Lunar Geology, Ames Research Center, NASA, 1974.

     Murray, Bruce, Michael C. Malin, and Ronald Greeley, Earthlike Planets, W. H. Freeman and C0., San Francisco, 1981.

     Papike, J .J ., S.B_ Simon, and J .C. Laul, The lunar regolith: Chemistry, mineralogy, and petrology, Reviews of Geophysics and Space Physics, 20, 761-826, 1982.

     Returning to the theme of bootstrapping for a bit, let's examine what kind of material processing could be done with a modest payload. I'll cover two scenarios, lunar surface and captured asteroid; the first post will discuss the moon.

     As with all unproven technology, mass estimates for mining equipment are wild guesses. I'll be using the wild guesses of people smarter and/or better informed than myself. Most of the concepts presented are well-known; I've simply combined them a different way and extrapolated the results.

     For those not interested in reading the wall of text to follow, here are my results:

3x haulers based on NASA chariot / lunar electric rover (1.2 ton each)
3x prospecting package: gamma spectrometer, neutron spectrometer, UV/VIS/IR spectrometer, magnetometer, robotic scoop (included in hauler mass)
2x excavator equipment package: bucket and cable rig, sized to fit hauler chassis (up to 3 tons each)
60kW power center (1 ton)
6x 90m² solar reflecting ovens with electrodes (0.5 tons each)
ore separation / benefication (0.5t)
cryogenic oxygen plant (4t)
tank press (0.5t)
radiators (2t)
electrical cables, 6ga/10.5mm, 4-conductor, 108v 3phase, 6kW, 8km (4t)
4000x cryogenic tank valves (0.2kg each)

total: 25.9t
(1 SLS or 2-3 Falcon heavy)

yield:
     - 2,400 tons of material processed per year, 10 tons per lit day
     - 840 1m³ filled oxygen tanks per year (958t LOX + 95.8t aluminum)
     - 128 1m³ filled water-ice tanks per year (120t H2O + 1.2t aluminum)
     - 527t metals (iron, additional aluminum, titanium, calcium) per year
     - 480t silicon
     - Unknown quantities N2, trace metals, other volatiles
     - ~217t refractory slag (radiation shielding); can be pressed, sintered and metal-wrapped

     The supply of valves is enough for four years; they are brought along because they are too complex and risky to assemble in place. A pressed and sintered (or SLS + heat treated) pressure vessel is simple enough to be produced on-site even if welding is required. Sufficient oxygen will be available for burst testing the results before use.
     If significant amounts of nitrogen are found, that would also be liquefied and tanked. Hydrogen would be reacted with oxygen and stored as water.
     Cables can be eliminated at the cost of more batteries and shorter range.
     Minimal additional equipment (1-2t) can enable production of thin-film solar panels with quarts front-glass and aluminum, titanium or iron backplates.



     Back to the long form...

     A moon expedition would produce huge amounts of oxygen. The main use for this would be to transport it to low-Earth orbit and pair it with hydrogen launched from Earth (or collected elsewhere) for fuel or for water. 1 ton of water contains 888.9kg oxygen and 111.1kg hydrogen; 1t of hydrogen from earth could be paired with 9t of oxygen from the Moon to yield 10 tons of fuel or water; this 10:1 ratio provides significant savings. For manned exploration of the moon, having oxygen available at each step of the trip saves much more than 9:1 since it does not have to be lifted from Earth and then sent to the Moon. For a cargo trip to Mars, the Earth departure stage calls for anywhere from 90 to 115 tons of fuel; using Lunar oxygen frees up 81-103 tons of payload to LEO or eliminates an entire SLS launch of fuel. A Mars campaign that requires four cargo trips and two manned trips could save six fuel launches or about $4.5 billion over six years. A single SLS launch could deliver a payload to the Moon capable of producing the ~600 tons of oxygen in one year as well as the vehicles necessary to deliver it to LEO; even if that mission costs $750 million for the rocket and another $1 billion for the payload it would save $2.75 billion while validating ISRU technology prior to its use on Mars.

     For a variety of reasons, the most useful place for a single mining operation on the moon is at either pole.

     Problem: The moon rotates at the same speed that it orbits Earth (it is tide-locked; the same face of the moon always faces Earth). Since the moon's orbit is about a month long, each day has two weeks of daylight and two weeks of night at the equator. That means enough power to run for two weeks of darkness has to be stored during the lit hours; most industrial processes would have to be halted.

     Solution: High peaks or crater rims near the poles can be sunlit for 80% of the time or more. (due to the axial tilt and geography there are no permanently-lit areas at ground level.)      A base at one of these locations could operate at full power for around 22 out of every 27 days.

     Problem: The moon's soil or regolith is bone dry to at least 30cm deep, and it seems unlikely that there is any bulk ice under most of the surface. Metals (titanium, aluminum, calcium, iron, magnesium), silicon and oxygen are abundant but hydrogen, carbon and nitrogen are exceedingly rare.

     Solution: There are craters whose bottoms are never lit by the sun, conveniently located next to the high-sunlight peaks. These areas get so cold that they can freeze water and volatile gases (including nitrogen); this is why they are called cold traps. There is strong evidence of water ice, hundreds of millions of tons of it, at the north polar craters and no reason to suspect it is not also abundant at the south polar craters (Shackleton crater).

     Result:
The mission should target either the Shackleton crater rim near the south pole or the rim of Peary crater near the north pole.

     Remaining problems: many.


     Rich sites to be mined need to be identified with some kind of sensing instrument (or more likely a set of 2-3). Nearly all of the major minerals on the moon can be processed for oxygen, but some of their metals are more useful than others.
     Estimates for volatile concentrations are as high as 5% for the target areas. Let's assume the bulk excavation of material yields 1% volatiles and further assume that it is nearly all water (either free as ice or bound as hydrates). There is some free hydrogen from the solar wind and potentially traces of hydrocarbons and nitrogen-bearing organics, but without enough data to even guess at a concentration. It is possible that there is bulk water ice available; if so, it can simply be melted, filtered and frozen again in tanks with minimal energy requirements.
     Just like on Earth, craters on the Moon were caused by asteroid or comet impacts. Many of these impactors are rich in metals (iron-nickel-cobalt and platinum group metals), while others are rich in carbon. It is possible that these sites will serve as rich orebodies for these resources. There are also a few areas where mantle material is exposed; this boundary layer is rich in incompatible elements like rare earths.

     Products of this early mission would be water, hydrogen, oxygen, base metals, possibly ceramics and possibly semiconductors. Later work would advance to construction of integrated circuits, LEDs and multijunction solar cells in addition to worked metal (bar, sheet, tube stock).

     A mobile excavator would be required, probably a simple dragline. I've seen proposals that assumed the regolith would be powdery and easy to scrape up, but the Apollo reports indicate that under a surface dust layer the soil was surprisingly tough. Some think that the grains have settled due to vibration from impacts over the past few billion years. Regardless, the tough soil and the possibility of crystalline ice means the excavator needs to be able to break up soils. In the low gravity of the moon, this requires either a very large amount of mass to produce the necessary force or a novel solution of some kind; either way will require a lot of power. I'm fond of the idea of a rotary flail since the impact force can be closely controlled, but that introduces a mechanical part that will wear over time. I am also fond of the idea of using a sheet or bag to cover the active area, something to capture flying dust and debris to avoid messing with the atmosphere and surrounding areas. Presumably this would use electrostatics to capture dust.      Due to the high power requirements I assume this excavator will be connected to the power center with a cable up to a few km long; this is one of the heaviest single items on the list but it is less risky than batteries or beamed power.

     See NASA DRM5 numbers; they propose an excavator system that is under 1t all-inclusive and redundant, including onboard power via electrolysis.

     Once the raw material is excavated it has to be processed. Options include baking out the water at the excavator or hauling it back to a refinery. I prefer hauling it back to reduce thermal pollution (that is, to avoid cooking off the useful volatiles in the mining area). So, this introduces the need for a hauling rover of some kind. The output of the excavator will drop directly into the bed of the hauler, with an electrostatic dust sheet over the top.

     The hauler will deliver regolith to the processing center. Samples will be analyzed for content in order to determine the most efficient processing plan. Volatiles like water will be baked out using solar concentrators at 600-1000 °C and then cryogenically separated. The remaining ore is now stable and can be stockpiled for later processing if needed. Iron-rich nodules and fragments will be removed with a magnetic rake. The remaining grains can be sorted with a rotary device into bins based on grain strength (aluminum-rich, titanium-rich, glasses) anywhere from 50% to 90% enriched.

     Many proposals assume the use of a reactant gas (usually hydrogen) which will be recycled; this gas is used to extract oxygen at lower temperatures than would be required otherwise. This seems unreasonably optimistic; hydrogen gas is difficult to contain on Earth, but we're talking about a hard vacuum environment with the most hostile abrasives we've ever encountered in the natural world. It will have to handle hundreds to thousands of open/close cycles with a perfect seal in the face of 1500+ °C temperature swings. Add the lack of maintenance or human operators for adjustments plus the need for vacuum pumps with both high volume and very low pressure and that all adds up to heavy, complex and unreliable.
     I choose to assume a brute force method of direct molten electrolysis. Instead of using hydrogen and reducing iron oxides at 1600 °C, the processor will melt the ore grains at 2200-2500 ­°C and electrolyze the melt with tungsten electrodes. This will produce oxygen gas at one end of the cell and reduced metal at the other end. For the lighter metals (aluminum, calcium, sodium) the cell temperature is high enough to vaporize them; the metal vapor can be collected on cold plates and scraped off as fine grains or it can be used directly for vapor deposition. Heavier metals (iron, titanium) will accumulate as melt and can be tapped and formed into bars. High-temp refractory ceramics like magnesia are out of reach of this method but might be available to a solid-phase electrolysis process. The oxygen is passed back through the incoming ore stream for heat exchange; any unreacted contaminants will definitely be oxidized in the process.
     Concentrated ores can be heat-treated further as a form of distillation to remove materials in order of their melting points; a carefully-designed feed mechanism can pass the ore through one oven, allow the lower-temp material to melt, then deliver the higher-temp material to another oven. The temperature of the refining furnace can also be adjusted to evaporate out metals in sequence with reasonably high purity. One additional control is the voltage of the electrolysis cell; if necessary the oven can be operated as a batch process using appropriate voltages to reduce each metal in sequence.
     The processor requires a very high temperature furnace. This will be made of magnesia (magnesium oxide, melting point 2852°C) and heated with a mix of joule heating and concentrated sunlight, which will require a large reflecting area of aluminized mylar. The magnesia is very heavy; it may be possible to construct a suitable trough on-site from regolith baked, pressed and sintered into a useful form. At this stage in the process the ore grains have been heated to recover most of the volatile content; the melt can be performed in open vacuum for direct solar heating with only the electrode sections enclosed to capture products. This avoids the need for an absurdly high-temperature transparent material. The furnace will be continuous process; accumulated solids are scooped out and dumped (and possibly used as a heat source for the first baking step). These can be compressed in the tank press to form radiation shielding blocks if desired. Oxygen is continuously produced and passed back up the ore stream, then cooled and passed to the cryogenic plant. Reduced metal either vaporizes and is condensed on a cold plate or deposition target or is drawn off as a liquid from the bottom of the melt and cast into the desired form.

     As a specific example: aluminum-rich grains will be melted (2072°C) in a magnesia crucible by concentrated sunlight and then electrolyzed (with tungsten, tungsten carbide or molybdenum electrodes) into oxygen and aluminum metal. The temperature can be further increased to 2470°C to produce aluminum vapor; thin-film conductive/reflective coatings or vapor deposition can be performed directly in the furnace. Aluminum metal parts can be controllably oxidized using the hot oxygen stream to form alumina surface coatings for abrasion resistance. This requires about 3.2MJ/kg from 0°C to 2100°C; 80-90% of this can be from sunlight, about 40m² of reflectors and 6kW for 1 kg per minute capacity. 52.9% of the yield is aluminum and 47.1% is oxygen by mass, barring any other metal oxides in the melt.

     As it turns out, tungsten is not suitable for this process over the long term because it is oxidized. An inert surface layer of iridium is required on the anode (oxygen-generating), while molybdenum is sufficient for the cathode (metal-generating). The anode layer needs to be thick enough to resist abrasion from any unmelted grains. A cylinder furnace of magnesia with molybdenum cathode strips along the bottom and an iridium-coated tungsten anode bar along the long axis will be used; the entire furnace is sealed and heated by concentrated sunlight from the outside. Preheated ore grains are loaded at the top of the 'near' end with an augur. A baffle keeps gases contained but the melt's surface is exposed to vacuum at this end; if this volume is enclosed then a cold plate could capture volatiles that were missed by other process steps. Oxygen is tapped at the top of the far end, while molten metal is tapped near the bottom of the far end. The endcaps of the furnace can be removed so any accumulated slag or debris can be removed and electrodes can be replaced.
     In order to boil the aluminum metal, the entire furnace's operating temperature is driven higher. Care must be taken to keep the oxygen gas and aluminum gas separate; if this mode of operation is desired then the internal structure should be shaped like a U, with cathode and anode in separate arms.
     There are ongoing efforts within NASA and within the steel industry for developing robust molten oxide electrolysis cells; a prototype molten regolith cell might contain 0.02m³ of volume and consume 3-5 kW of electricity as a 100% joule-heated furnace (with no mention of cycle time). My proposal needs to process 10m³ per day but can obtain very large amounts of heat externally; as a result my design can place the electrodes closer together, reducing the resistance of the melt and thus the electrical losses to heat.

     This method can be used for extracting iron, calcium, sodium and titanium from their oxides as well. While useless on earth, pure calcium is an excellent conductor in dry, oxygen-free environments and could substitute for aluminum in PV conductor lines. Sodium and calcium are potential scavengers for corrosive volatiles like chlorine and fluorine, but their vigorous reaction with water calls for careful process management.

     Silica grains can be used to make clear glass. Thin quartz glass sheets are a starting point for making PV cells (the surface protective layer); conductive lines of aluminum are vapor-deposited onto the glass, then doped silicon, then a thicker layer of aluminum. These are not the most efficient devices (~9%), but they are very simple and straightforward to manufacture. The silicon can be extracted from silica just like the aluminum is refined, but at a lower temperature (1713°C).


     With a goal of 1 ton of 1% icy regolith processed per day we should be producing 10kg water, 400kg oxygen, 200kg silicon, 120kg iron, 60kg aluminum and about 260kg of other metals and unprocessable byproducts. Specific ratios of silicon, iron, aluminum and titanium depend on what minerals are present at the excavation site, but it is very difficult to predict in advance what the ratios will be at a specific site. This processing will require roughly 30m² of solar reflector area and 4.5kW of electrical power. If we assume the initial power system alpha is 200 watts per kg (since it needs to withstand lunar gravity), that's only 22.5kg of solar panels.
     Pushing things a bit farther, 10 tons of ore per day would require 45kW of power (225kg) and 400m² of reflector area (about 8kg plus supports). A minimum work cycle of 20 days per sol means about 2 tons of water, 80 tons of oxygen and 52 tons of metals per sol (27 days). If the excavator manages to produce ore with 5% ice then the yield is 10 tons of water per sol; if bulk ice is discovered then a different process will be needed. It would be possible to process larger quantities of ore for volatiles and only process a portion of the desired metals; extracting water takes a tiny fraction of the energy needed to melt and electrolyze metal oxides.

     See the NASA DRM5 numbers for ISRU equipment; to produce 56kg H2O per day from 3% water-content soil required 413kg of equipment and 2.02 kW of power. That's roughly 1.8 tons ore per day; multiply by six to hit the 10-ton target and that's 2.5t of equipment and 12kW of power for the entire process end to end. Most of the power is used for process heat, so substantial savings can still be obtained with solar reflectors. This would produce a supply of dry granular material for later processing or for direct use as bulk shielding.

     The excavator needs to remove a bit under 7kg per minute. Bulk density is around 2g/cc (2ton/m³). A 100-liter bucket would have to be filled about every 28 minutes. If the hauler holds 1 ton (cube 80cm per side) then a full round trip (load, deliver, unload, return) must take 2 hours and 24 minutes or less. Assuming load and unload take 12 minutes that leaves 1 hour for the drive one-way; better yet, let's assign 1.5 hours for the loaded trip and 30 minutes for the empty trip. At 5 m/s maximum empty speed (1.67m/s loaded speed) that gives a range of 9km between refinery and excavator.
     If the hauler holds three tons (100x100x150cm) then a full trip is at most 7 hours 12 minutes. Using the same 12 minutes to load or unload and 3/4 of the trip time loaded, that's 5 hours 6 minutes for the loaded trip and 1 hour 42 minutes for the return trip. Using the same speeds (5m/s empty, 1.67m/s full) that gives a range of 30.6km.
     An alternative is to use both haulers in rotation; one is stationed at the excavator getting filled while the other travels to the refinery and back. There would be enough time for prospecting during the return trip.

     NASA already has an electric rover design in this size range; 1 ton of vehicle mass for 3 tons of payload. That design's maximum speed is quoted several different ways, but at least one reference uses 15mph (6.7m/s) as high-gear speed, presumably for just the chassis, and several others use 10km/h (2.78m/s) as the top speed while loaded with a mobile habitat module. I would add prospecting sensors, a small scoop and a blade and auger.

     For reasons of efficiency, the excavator should use a hauler chassis with an excavation package mounted on top. A spare chassis can be shipped in case either the hauler or the excavator fails. Resupply missions can carry modular parts. Two excavation packages will be shipped with the initial mission, both using a drag line arrangement that minimizes repositioning time. (A set of two pylons with pulleys, so the bucket can be moved anywhere within a triangle defined by the two pylons and the hauler base. A 50m triangle with 450m of cable can cover 1082m² of territory; for excavation to 2m that's 2164m³ or about 4300 tons, more than a year of production.) All three haulers will be equipped with a blade and augur. In fact, the initial phase would involve all three vehicles using just their blades to clear a landing site for cargo spacecraft, followed by a short roving mission to identify high-ice sites and then leveling a basic road to the best site. This will provide some ground truth on solar wind ions and other volatiles in the upper regolith plus validate several approaches to lunar base site clearing for manned missions.

     Harvested metal (primarily aluminum) is pressed into cryogenic tanks using multipurpose valves brought from Earth (solenoid with integrated pressure relief). These tanks are pressure-tested and then filled with liquefied oxygen. Filled tanks are stored in a permanently-shadowed crater for zero boiloff. Tanks are shipped to L1 for about 2.5km/s dV in a dedicated lander, then to LEO for a further 0.8km/s in an orbital tug with heat shield or 3.8km/s propulsive-only. Ideally a launch sling would be used to deliver the tanks to L1/L2 and avoid the need to burn propellant.

     Once this architecture is validated it could be reapplied at other sites and for other purposes. The haulers could be shipped to a future human lunar base to clear landing sites, roads and construction sites, plus accumulate material for radiation shielding and later bury the habitats. The processing equipment could manufacture solar panels, heat radiators, oxygen, structural materials, etc. in advance of crew arrival so the mass to be shipped from Earth can be minimized.
     Similar equipment could be shipped to Mars for the same purpose; the initial cargo mission could deliver equipment for site preparation and atmosphere processing. Mars has a much more complete chemical environment, so a much more useful selection of products can be produced.

     Again, NASA DRM5 has useful numbers for PV power systems. A single PV/RFC (regenerative fuel cell) module was 4.5 tons and provided 5kW of fuel cell power and 290m² of collector area at 29% efficiency. Under lunar conditions (no atmosphere, 1366W/m², ground return ignored) that array produces 396 kW gross, roughly 336kW of conditioned power. The whole system could be reduced to one fifth, massing 0.9t, providing 1kW of fuel cell power and 67.2kW of PV power. This would be abundant power for daytime operations but probably insufficient night-time power. However, the fuel cell's peak output would be more than sufficient, so extending operation to several days would require only larger tanks for water, O2 and H2. This is reasonably in line with my original estimate of 1t for 60kW.

     Further, the DRM5 offers a nuclear alternative. A 30kWe nuclear reactor masses 7.8t and would enable continuous operation. I think this would be an enabling technology that would completely change the architecture of a lunar mining operation. Night on Luna is the enemy for solar-powered architectures, leading to deep thermal cycling and heavy battery or fuel cell requirements. It also greatly expands the potential locations for a base. There would still be a need for rover excavators; nuclear power means a lot of radiated heat that we want to keep away from the cold-trap volatiles we are most interested in harvesting. One benefit is that the reactor's waste heat can be used as a first stage heat source for ore processing. Using JIMO (project Promethius) data, the proposed brayton cycle reactor has an end to end efficiency of 18.35% from thermal to conditioned electrical power at the PMAD output. The Mars design has slightly improved efficiencies, but JIMO performance would be sufficient. Let's assume the difference means a 30kWe reactor would mass 8t even and spec 163.5kWt. This reactor's coolant is 920-950K at the recuperator, a very convenient source of process heat at 650-670 °C and around 133kWt available.
     Lunar soil's specific heat is 0.88 kJ/kg*K at 350K; data is sparse for higher temperatures but can be expected to increase somewhat up to 950K; let's call it double or about 1.7kJ/kg*K. That would mean the available heat could cook soil from 90K to 950K at a rate of 5.46kg per minute. 10 tons processed per day would be 6.94kg per minute, so we are in the right ballpark. A counterflow heat exchanger running between the incoming ore and outgoing ore would only need to recover about 22% of the heat to close the thermal requirements.
     If relatively pure water ice is available, it can be taken from 90K to 275K (2 °C) for ~334kJ/kg + 334kJ/kg to melt it. The reactor could process 23.9kg of water ice per minute; this application would use heat at the radiator return (~390K) rather than the recuperator for more efficient operation. This approach could handle up to 34.4 tons of water ice a day.
     Both of these modes of operation would leave the entire 30kW of electrical power available for other purposes

• 

Lunar Materials Production

Label	Build Upon	Additional Processes (cumulative with "builds upon")	Additional Materials Produced (cumulative with "builds upon")
1	N/A	Sieve and/or grind regolith	Regolith
2	1	Molten Regolith Electrolysis	“Mongrel Alloy” Ceramic Oxygen
3	1,2	Vacuum Distillation or equivalent	Elemental Aluminum, Iron, Magnesium, Calcium, Silicon, Titanium. (Also, if regolith obtained from KREEP terrane, then Potassium, Rare Earth Elements, and Phosphorus)
4	1-3	Metals Refinery	Good alloys
5	N/A	Ice Mining & Distillation	H2O, CO, CO2, NH3, many compounds and trace metals
6	5	Fischer Tropsch process	CH4, plastics, rubbers
7	1-6	Metals Refinery including carbon from 5 & 6	Steel
8	1-3	Slaking and cement production	Lime and cement
9	1-8	Advanced processes	Anything you want

• 

• 

Based on an earlier proposal, the method is a three-drum slusher, also known as a cable-operated drag scraper (Ingersoll-Rand Company 1939, Church 1981). Its terrestrial application is quite limited, as it is relatively inefficient and inflexible.

The method usually finds use in underwater mining from the shore and in moving small amounts of ore underground. It uses the same material-moving principles as more efficient, high-volume draglines.

The slusher is proposed here because the LOX-to-LEO project is a very small operation by terrestrial standards and requires a method that minimizes risk. The three- drum slusher has already proven itself in this context. It has the advantages of simplicity, ruggedness, and a very low mass to be delivered to the Moon. When lunar mining scales up, the lunarized slusher will be replaced by more efficient, high-volume methods, as has already happened here on Earth.

The Machine and Duty Cycle

Before discussing the advantages of the machine in a small-scale startup lunar mining scenario, I will describe the slusher and its duty cycle. It consists of the following modules (see figs. 18 and 19):

1. A mobile power unit and loading station—including three drums around which the cables are wound, a mechanism to place anchors, a mechanism to change tools, an optional operator cab, a dozer blade, and a conveyor to load material into the electrostatic separator
2. Three lengths of cable to operate the scraper or other mining tools
3. Two anchored pulleys
4. Interchangeable working tools, including scrapers, rakes, plows, and rippers

The duty cycle starts with machine setup. The mobile power/loader unit places two pulleys at appropriate locations at the mine site. They could be anchored by large augers in the firm regolith below the loose soil or by other methods. The preferred anchoring method depends on specific site characteristics. After the pulleys are anchored, the power unit similarly anchors itself. The two pulleys and the power unit form a V-shaped mining area. Because machine setup is done only infrequently, is a complex job, and requires firm anchoring, it could be left as a manual operation. For one reason, the anchoring augers might hit buried rocks before they are successfully emplaced. Further study may show that automated or teleoperated setup is also feasible and more desirable.

• 

However, I will mention one major alternative—a stationary power/loader unit (fig. 20), which is the terrestrial configuration. In this case, the slusher itself would be far simpler, but such a system would require an auxiliary vehicle to transport the slusher from site to site and set it up. A stationary slusher would be less able to remove unexpected obstacles from the pit, as I will discuss. Either way, the excavation duty cycle is basically the same.

After setup, the excavation duty cycle begins with the scraper (or other tool) at the loading station. The scraper can be moved to any point within the V by a combination of tensions on the two outhaul cables. After reaching the desired position, usually as far into the pit as possible, the scraper is pulled back to the power/loader unit by the inhaul cable. During inhaul, a combination of inhaul force and scraper weight causes the scraper to fill with loose regolith and carry it back to the power/loader unit. Here the material is pulled up the ramp, discharged from the scraper onto the conveyor, and loaded directly into the mill module.

The mill is the electrostatic separator described by Agosto in the section on beneficiation. The separator should be in direct contact with the slusher. This eliminates rehandling of the mined material, resulting in a significant energy saving, since 90 percent of the mined material will be rejected by the separator. The waste from the separator is dumped away from the production area by ballistic transport or another method. Waste transport need only be far enough to keep the separator and slusher from being buried in their own waste.

The box-like scraper will have closed sides to keep the very fine regolith from spilling out, as has been the terrestrial experience.

Because the machine defines its own mining area and machine motions are repetitive, the scraping operation is a reasonable candidate for automation. Feedback control for automatic loading of the scraper will be supplied through sensing the inhaul cable tension. Loading always requires complex motion control, but the problem is more easily resolved with a limited-motion machine such as the slusher than with fully mobile equipment, such as front-end loaders, which have unlimited freedom of motion.

After mining starts, the mobile power unit generally does not move. If an obstacle is uncovered in the pit, the mobile version of the power/loader unit can detach from its anchor and move into the pit. (The anchor is not removed from the soil unless the machine is moving to another site.) To facilitate pit work, the loading ramp is tilted up and a dozer blade extends to its working position. The blade can push boulders out of the pit or mine a small selected area. Because the power/loader unit is lightweight and consequently has poor traction characteristics, it must pull against the outhaul cables when it works a load in the pit. The complexity and uniqueness of this job argue against automating it, but automation is not impossible and teleoperation is a possibility. Both setup and power unit pit work can be done by teleoperation, except for handling severe unforeseen problems that require human intervention.

During normal operation, electric power is supplied to the power/loader unit by a stationary cable. When the power/loader unit works the pit, it gets its power through a cable reel located at the anchor. One advantage of stationary mining equipment such as the slusher (even the mobile version moves very little during excavation) is simplicity of power supply. Most mobile terrestrial equipment has diesel power, which is rugged, capable, efficient, and, most importantly, onboard. These loaders are very flexible and rugged earth-movers. The lunar alternatives are less satisfactory. Lunar loaders with onboard power would probably use electric motors driven by fuel cell or battery technology. Both are expensive options. Versions with external power must be fed electricity through a trailing cable. Terrestrial experience has shown that trailing cables are high maintenance items, but adaptation to the Moon is possible. Another possibility is a new-technology internal combustion engine, but developing the engine and finding lunar fuel sources are difficult problems.

The Lunar Environment and Machine Design Principles

The major reason for proposing the three-drum slusher is to illustrate problems to be expected in a lunar mining project.

Simplicity in Design and Operation

Compared to other mining machinery, the three-drum slusher is quite simple in design and operation. This simplicity yields several interrelated advantages.

1. Fewer moving parts, resulting in fewer failures per operating hour
2. Simpler repair, reducing downtime after a failure
3. Smaller inventory of repair parts, hence less weight to transport to the Moon
4. Simpler parts, with faster adaptability to lunar manufacture
5. Less redesign for lunar conditions, with consequently lower R&D costs
6. Fewer degrees of freedom than mobile equipment, and therefore relative ease of automation
7. Fewer project startup problems

Traction Independence

Mobile mining equipment depends on traction to generate sufficient loading forces on the blade or scraper. Most terrestrial mobile equipment loads near its traction limit. On the Moon, reduced gravity creates a less favorable inertia:traction ratio. Increases in traction are achieved by increases in mass, but increases in mass add inertia, which decreases control of a moving machine. To achieve the same traction as on the Earth, a mobile machine on the Moon would have to have six times as much mass. This greater mass would cause correspondingly higher inertial resistance to turning and slowing.

Slusher loading forces are supplied through the cable, thus almost eliminating traction problems. The scraper bucket will have to be more massive than on Earth, simply to cause the bucket to fill. To lower launch weight, the extra mass needed by the scraper bucket can be supplied by lunar rocks.

Since the slusher is a relatively low-production method, upscale lunar mining projects will eventually use mobile mining methods. It is necessary to address inertia- traction problems as early as possible. Further study may find that long-term considerations argue for using mobile equipment from the very beginning. As with the scraper bucket, the extra traction mass can be supplied by lunar materials. Perhaps traction could be improved by new tread or track designs.

Mining Flexibility and Selectivity

The lunar slusher differs from the terrestrial slusher by one major design addition: the power unit is mobile rather than stationary. This allows the machine to set itself up and eliminates the need for an auxiliary vehicle. Most important, by adding a dozer blade, the machine can doze undesirable rocks from the pit. Such large rocks would impede mining operations if the power unit were stationary.

The mobile power unit makes the machine more selective. By allowing the power/loader unit to reposition, the slusher has some ability to separate different soils during the mining process or to go into the pit and mine a small area of interest.

Mining Tools for Selecting Particle Size and Breaking Regolith

The ability to change from a scraper to a rake allows the machine to select different size fractions. For example, if fines are required, the area can be raked on the outhaul, so that oversized rocks are moved to the far side of the pit. Then the rake can be exchanged for a scraper to mine the remaining fines. If larger sizes are desired, they can be raked in on the inhaul.

Other tools, such as rippers or plows, are used to break difficult ground. Lower levels of lunar regolith appear to have a high degree of compaction (Carrier 1972) and must be broken before mining can take place. Although it is the usual terrestrial practice, chemical explosive blasting appears to be prohibited by the high cost to transport the explosives to the Moon. The ripper or plow greatly increases machine working depth. It has already been established that the slusher, unlike mobile loading equipment, is independent of traction. This traction independence allows the slusher to break difficult ground while still maintaining a light weight. More lunar geotechnical engineering data is needed, however, and the design of the ripper is unknown. The ripper probably needs an attached weight to force it into the regolith. A plow may be better than a ripper, as its shape helps pull it into the soil, making it less gravity dependent.

---

Two Environmental Factors

In addition to one-sixth gravity, there are two other significant lunar environmental factors worth noting: temperature extremes and electrostatic dust. Temperature extremes are easily answered by shutting down during the lunar night. Heating selected equipment components is feasible, if more expensive. Electrostatic dust is more of a problem. Machinery bearings must be protected, a problem exacerbated by the lunar vacuum, where lubricants may evaporate. One significant feature of the slusher is that it uses very few bearings, even in the mobile version. Lunar bearing designs and lubrication methods must be developed regardless of the mining method used.

Machine Specifications and Fleet Mix

The specifications and fleet mix I present are for the mobile lunar slusher. The reader should note that alternative methods, such as the stationary slusher, were included to illustrate lunar mining design problems and are not specified here. The data given below are for the proposed baseline mobile lunar three-drum system.

The needed raw material for a 100-metric-ton LOX-to-LEO project is 40 000 metric tons. The machine specified below is oversized by a factor of 2.5 or a yearly rate of 100 000 metric tons. This oversizing is to ensure the production is easily accomplished, while demonstrating that a significantly oversized machine is relatively lightweight. Even with this large oversizing, the hourly production is about 25 metric tons per hour. This rate is close to the lowest rate shown on the production table of one manufacturer.

Specifications
Yearly production	100 000 metric tons
Span and reach	50 meters
Mined depth	2 meters
Scraper capability	2 cubic meters
Mobile slusher weight	4.5 metric tons
Auxiliary vehicle weight	1.5 metric tons
Ballistic transporter	1 metric ton
Spare parts and tools	2 metric tons
Operation and maintenance	2 people
Foundry (optional)	5 metric tons
Total weight (without foundry)	9 metric tons
Fleet
mobile slusher	1
auxiliary vehicle with small multipurpose crane	1
ballistic transporter	1

Lunar Mining Operations

Production Profile

The baseline self-propelled slusher excavates a triangular area 50 meters in base and height. At a mining depth of 2 meters, approximately 9000 metric tons are excavated per setup. Approximately one setup per lunar day yields a yearly raw material production of 100 000 metric tons. Mining would cease during the night, as the extremely low temperatures would make operation difficult. But milling could continue, as the mill is more easily protected from the environment.

---

Modular Components

Every opportunity should be takento divide the slusher (and other equipment) into modular components. The modules should be as interchangeable and transportable as possible. Two general types of modules envisioned are large functional modules, such as mining units, material crushers, and electrostatic separators, and small equipment modules, such as electric motors and power distribution panels.

Modularity increases flexibility and reduces downtime without adding equipment weight.

1. A component needing repair can be replaced on site with a working unit. The defective unit can then be repaired onsite or in the shirt-sleeve environment of a pressurized shop.
2. Quick component replacement allows production to continue when one component breaks. When many components break, a producing unit can frequently be assembled from the remaining units.
3. Catastrophic failure of a module, such as an electric motor, will not hamper production, as the whole unit can be replaced.
4. Increasing production simply means adding more components rather than redesigning or rebuilding the existing facilities. Upgrading one part of the operation with new designs or technology is facilitated by replacing the old components with the new.

Accomplishing modularity is relatively easy in small-production mining facilities-: (By terrestrial standards, the lunar slusher operation is very small.)

Auxiliary Vehicle

A small, self-propelled auxiliary vehicle will probably be necessary, even with a mobile slusher or other mobile mining method. It will find use hauling broken components to the repair shop and replacement modules to their operating positions. as well as hauling people and materials back and forth. It should have a crane to aid in constructing habitats and repairing equipment. Adding a small conveyor to the vehicle would allow it to heap up Joose regolith for habitat shielding. This general-purpose vehicle will be smaller than the vehicle required to move a stationary slusher from site to site.

Shop Facilities

A pressurized repair shop would facilitate complex repairs by providing a shirt-sleeve environment. There is no good reason to rewind an electric motor in a vacuum. Since lunar dust is ubiquitous and insidious, some system for removing dust from the shop and its equipment must be provided. Equipment from the outside must be cleaned of dust before it enters the shop.

However, a shop would add significant launch weight unless it could be fabricated on the Moon. launch weight considerations dictate a careful mix of tools, equipment, and spare parts for the shop. The shop and repair activities are there to keep the mine operating while helping to keep transportation costs for tools and spare parts to a minimum.

In addition to tools and spare parts, the shop could eventually have a small adjacent foundry to cast pulleys, bearings, and other easily fabricated parts. The foundry will probably not be in the shop but outside in the vacuum. This plan assumes lunar metal production.

Fiberglass ropes of lunar origin to replace Earth-made cables are also candidates for early lunar manufacture, as glass is a byproduct of LOX production. Glass manufacturing methods were not considered here.

Mine Waste Disposal

Depending on required products and milling processes, some fraction of the mined material will be waste which must be removed from the production area. This fraction can be quite significant (e.g., terrestrial copper operations yield only 10 kg of product per metric ton of ore; thus, 1990 kg of that tonne is waste). The LOX-to- LEO project will generate two types of waste. Fines waste is the soil fraction rejected by electrostatic separation. Slag waste results from the smelting process. Production of liquid oxygen from regolith that is 10 percent ilmenite will generate mostly fines waste, on the order of 90 percent of the material mined or 36 000 metric tons per year. Providing a vehicle for waste disposal would add significant launch weight, and the waste disposal options must be studied.

Robert Waldron and David Carrier have both proposed a ballistic transport mechanism that could be usable in lunar mining. It is well suited to removing fines waste. Using a simple mechanism such as an Archimedean screw or conveyor flights, it is possible to ballistically transport fines waste several hundred meters away from the production area. Their preliminary calculations indicate that the mechanism could be built at a reasonable weight. A ballistic transporter, along with a storage and feed bin, could be added as part of the mill module or as a separate module. The ballistic transporter could also be used to heap up material for habitat shielding.

Ballistic transport of the glassy slag waste from the smelting of ilmenite will be more of a problem. For regolith that is 10 percent by weight ilmenite, the slag waste produced will be on the order of 80 percent of the ilmenite or 3200 metric tons per year. Slag waste will contain much larger and more angular particles, which are less suited to ballistic transport. If the iron is extracted, the slag waste drops to 40 percent or 1600 metric tons per year. These figures are based on 100-percent separation efficiencies.

     Continuing the series, this is a look at what to do next after water mining becomes routine and a network of fuel transfers is available. This post assumes that Lunar water mining is operational, but that material from Mars is not guaranteed.

---

     While harvesting ice is fairly straightforward and something I expect we can automate, surveying mineral resources for efficient mining is altogether different. It would still be possible to do without humans on-site but I believe sending experts would be more effective. A program of manned exploration alongside current state of the art automation would expand our knowledge of the Moon and our experience with autonomous mining. Still, the general program I will describe could be done with or without people on site.
 Actually making use of these materials will require human hands. We do not have the automation technology available to perform complex assembly, particularly in a challenging environment. Individual steps will be automated as much as feasible, but in the near term most manufacturing processes will require a crew.

---

     Operations would be based at the polar water processing center. An abundant supply of fuel and power is available here along with frequent visits by fuel tugs. Hardware from Earth would be delivered to LEO, boosted to EML1 by a cargo tug and then relayed to the pole by another cargo tug. Some types of processing hardware would be left here, to become part of the resource processing infrastructure. Other types would be used on location to preprocess and reduce the mass that needs to be returned to base. Details depend on what specific hardware and process is being used.
     Travel would be by cargo tug, using suborbital hop flights. Surface transport (rover or moon buggy) might reach 1-2° (30-60km) from the pole, but the terrain is rugged. It would be possible to cut a rudimentary road to allow for safer ground travel if a valuable deposit was found. Until then, exploration would be done by hopping to a target site, mapping / probing the area, taking samples, then hopping back to base. Travel to points within 23° (698km) of base would require only 2km/s round-trip. An 83° (2518km) range would require 3km/s, while access to the opposite pole (5461km) would require 3.4km/s. The reference tug can deliver 29 tons to EML1 or could carry 20 tons to any site on the surface and 60 tons back for 63 tons of fuel. For sites within 700km of the pole that same 20-ton exploration package could bring back 80 tons of ore for 46 tons of fuel.

---

     The easiest initial harvest would be to run magnetic rakes through the regolith and collect iron nodules. The result would be bags of nearly pure nickel-iron grains. This should be done in the immediate area of the pole first to build up a stock of metals with minimal processing requirements. This can be done fairly easily by automated rovers and should be pursued while other exploration activities occur. Even if no other mining is performed, the material collected with this approach would yield iron and nickel as structural materials suitable for 3d printing (via SLS or thermal deposition of carbonyl), plus platinum group metals to use as electrode plating and catalysts.

---

     Most Lunar mining schemes are intended to produce oxygen, since most were designed before the widespread existence of water ice on Luna was known. (See for example this NSS article.)With such an abundance of water it makes little sense to go to a lot of effort specifically for O2. Instead, the two main targets will be aerospace metals (aluminum and titanium) and incompatibles (phosphorus, potassium, rare earths, etc.).

---

     Titanium-rich soils contain the mineral ilmenite, an iron titanium oxide. Much research has been done on this as a resource for producing oxygen and the general distribution and concentration of ilmenite at the surface is known. Concentrations can be as high as 10% titanium by mass, while the mineral itself is 31.6% titanium by mass. Impact sorting can produce an enriched feedstock of 90% ilmenite grains, which is 28.4% titanium by mass. This input would be reduced with hydrogen to form iron metal, titanium dioxide and water. The titanium dioxide is electrochemically extracted in a cell with molten calcium chloride and a carbon anode under the FFC Cambridge process, or is carbothermically reduced and then chloride-processed in the MER process.
         Aluminum-rich soils are formed of anorthosite, a calcium-rich plagioclase composed mostly of CaAl3Si2O8 with a small fraction (less than 5%) of NaAlSi3O8. This material is around 25% aluminum by mass. There are a few options for processing; countercurrent hydrochloric acid with fluoride ion (producing aluminum chloride), calcination (with or without carbon), arc melting and reaction with hydrogen. Partially refined aluminum (reduced alloys of aluminum, iron and silicon) can be further refined by the subhalide method, where aluminum chloride (AlCl3) at 1000-1200 °C reacts with aluminum metal to form aluminum subchloride (3 AlCl); aluminum metal is deposited in a condenser and the AlCl3 is recycled. The traditional ALCOA process can also be used, but this equipment is not easy to scale down and is very energy-intensive.

---

     Incompatibles are concentrated in KREEP (meaning potassium, rare earth elements and phosphorus). This material is about 0.4% phosphorus and 0.8% potassium by mass (present as oxides, each about 1% by mass). It also contains relatively high concentrations of rare earths, including 15-20 ppm thorium and about the same mass of lithium. This material is mostly located in Oceanus Procellarum and can be seen clearly in maps of the Moon's thorium concentrations. There are four specific craters with very high readings that are worth investigating; all are in the Earth-facing northern hemisphere.
     The main goal is to harvest potassium and phosphorus for hydroponics. Less-useful minerals would be removed and the resulting leftovers would be available for later intensive processing (most likely zone refining). Potassium oxide can react violently with water, so care must be taken; bioavailable forms are as chloride or nitrate. Phosphate can be purified by converting to phosphoric acid with additional processing, resulting in either ammonium phosphate or calcium phosphate.

---

     With a ready supply of structural metals, parts needed for spares can start to be sourced entirely from lunar materials. New hardware built on the Moon won't be under such extreme pressure to minimize mass, meaning the locally-produced equipment can be built heavy to improve MTBF and reduce spares. Simpler but less efficient PV panels can be constructed using all local materials, expanding the base's power supply. Light metals shipped to EML1 can be used to build extremely light structures that would fall apart under chemical acceleration; this capability would be a significant advance for electric propulsion and possibly for light sails. Oversized propellant tanks and other structures could be built to dimensions that could not be launched from Earth.

---

     This step represents the first major advance in self-sufficiency. No longer dependent entirely on parts and fertilizer from Earth, the facilities offworld can expand with minimal additional launched mass. There is a strong demand for carbon, nitrogen and chlorine, all of which are available in bulk on Mars. Still, the facilities begin to provide services to customers back on Earth, mostly as satellite maintenance but increasingly for satellite construction.

Part of my series on countering misconceptions in space journalism.

Water, the staff of life. What a shame, then, that the Earth’s Moon always seemed to be so dry! So dry, in fact, that in most places if there was concrete available it would be a better source of water than average moon dirt.

Not everywhere, though. For decades now, permanently shadowed craters near the pole have been thought to trap volatiles, including water, in their intense cold. More recently a series of missions have confirmed the presence of some water. Scarcely a month goes by without some breathless headline exclaiming NASA’s (re)discovery of moon water, complete with some Kerbal speculative art.

According to some enthusiasts, moon water changes everything. Yes, the moon is still a barren remote frozen boiling irradiated cratered hellscape, but since there’s some water near the poles, we can build bases with fountains and swimming pools, and make money by selling the water!

I’m actually good with all of this, except the last part. The problem is that there’s not that much water and it’s not that valuable.

First, the quantity. No-one actually knows how much water is there, but if we assume that the bottom of the relevant craters could be lined with 100m of frozen comet rubble, with a water concentration of 10%, then there could be a billion tons, or one gigaton, at each pole.

When I think of water I think of a nice lake full of fish. Instead, we have some cryogenically cold frozen mud that’s full of shards of metals, including heavy metals, and other crud. Still, it’s a lot better than the rest of the moon, which has water abundance of around 200ppm, and is drier than fresh dessicant.

One gigaton of water sounds like a lot, but it’s only a cubic kilometer. For comparison, there are many reservoirs on Earth that hold more water. Converted into hydrogen and oxygen it could fuel all of Earth’s combustion-powered vehicles for a couple of months. And then it’s gone. This fossil water took billions of years to accumulate, and it’s a non-renewable resource.

The second problem is that it’s not that valuable. Lunar water mining advocates envision a mine that produces rocket fuel and transports it to other places where it’s needed more, such as LEO. Here a tug could be fueled to transport geostationary satellites to their final orbits.

It’s worth noting here that water isn’t rocket fuel, it’s rocket exhaust. Turning water back into rocket fuel requires putting all the energy that fabulously energetic fuel generated back into the water, plus some extra for inefficiency’s sake. At 10 kWh/kg of hydrogen and oxygen, generating enough fuel to transport 100 T/month back to Earth would require an average of 30 MWh per day, or about 1.2 MW continuous power. For comparison, the ISS solar arrays generate about 100 kW when in full sun.

Unfortunately for this business model, the assumption that GEO launch cost would remain above $35k/kg has proven false. Indeed, continuous launch innovation on Earth has driven launch cost down by an order of magnitude, crushing the lunar water export model. For a more thorough analysis, see my blog on the topic. Fundamentally, the value added per kg of water or hydrolox fuel is much too low to be a good business, even on Earth!

Despite the hype, the fundamental economics are well understood by the mining industry. We don’t have to worry about a resource rush suddenly occurring, complete with moustache twirling monocle-clad capitalists and grieving moon environmentalists.

That aside, major conceptual work on lunar mining continues to this day. A source of water (and other light elements) is important for a lunar base, and lunar water fuel is great for flying hoppers around on the moon. Reducing mass requirements and shipping costs for a lunar base is awesome, but it won’t pay for the base itself. For that, we need something that has a very high demand and value density on Earth that can only be obtained on the Moon.

So when you see articles about lunar water, remember that it’s a very limited resource in a very particular place, and there’s no market demand for it.

      Jeffrey Allen is the principal investigator on a project “Low Mass, Low Power, Non-Mechanical Excavation of Gypsum and Other Evaporites and Water Production on Mars.”
      This two-and-a-half-year project, funded for a total of $500,000, will investigate whether robots sent to Mars can use powerful jets of water to excavate gypsum, blast the rocks to disintegrate them, and heat the gypsum particles to release the water bound within mineral’s crystal structure. This could be a way to expeditiously make more water and oxygen for human consumption and to make rocket fuel on Mars.
     This work aims to create a way for NASA (or a space exploration contractor) to send humans to Mars with enough water, oxygen and rocket fuel for the trip out, knowing that there will be enough water, oxygen and rocket fuel waiting on Mars for the astronauts to use on their trip home to Earth.

Breaking It Down

     If mining machinery breaks down on Earth, fixing the problem is expensive, but it’s also just a phone call away. There are no mechanics on Mars; therefore, coming up with a way to mine that causes the least wear on machines was the starting point for a project occurring millions of miles away.
     “How could you mine hard rock knowing these machines have to operate for many years without maintenance?” asks van Susante, senior lecturer in mechanical engineering-engineering mechanics and faculty advisor to the Mining Innovation Enterprise (MINE) team. “The problem is the metal that exerts the force to break the rock. Metal wears down or breaks off, requiring maintenance. We’re trying to eliminate that part of it. We came up with idea to use a water jet, or some other gas or liquid, that we can spray at high pressure at the rock. It’s a new idea in space that hasn’t been proposed before.”
     Working with Tim Eisele, assistant professor of chemical engineering and endowed faculty fellow, and students from the MINE team, van Susante is creating a sealed chamber in the Ore Separation Laboratory and Benedict Laboratory equipped with water jets to disintegrate gypsum samples. The second step is to transport the resulting slurry for separation to remove suspended particles and supply the water back to the pressure washer.
     Their plan is to feed water back into the system until there is a surplus, at which point the water will be stored. The water can then be separated and combined with carbon from the Martian atmosphere to create methane for rocket fuel andliquid oxygen is a byproduct.

• 

(ed note: I'm probably wrong, but it seems to me the mudskipper trick might have applications to the fluid gypsum chisel)

      A fish that uses water as a sort of tongue to feed on land could shed light on how animals with backbones first invaded land, researchers say.
     One of the most pivotal moments in evolution occurred when a few pioneering fish left the waterabout 350 million to 400 million years ago. These fish evolved into the first tetrapods (four-legged land animals), which ultimately gave rise to amphibians, reptiles, birds and mammals.
     To figure out how ancient animals made this shift to land, scientists typically investigate how the limbs of the first tetrapods evolved over time. However, biomechanistKrijn Michel at the University of Antwerp in Belgium and his colleagues suggest that investigating how early tetrapods learned to eat on land is equally important to understanding this key point in evolution.
     In the water, fish generate suction with their mouths to help draw in food with the help of a neck bone known as the hyoid. On land, sucking in air to swallow food proved impractical, so tetrapods instead evolved tongues supported by the hyoid that help guide food down their throats. However, much remains unknown about how tetrapod hyoids and tongues evolved.
     To learn more about the evolution of tetrapod feeding, the scientists investigated modern amphibious fish known as mudskippers that dine on land. Mysteriously, these fish emerge onto land with their mouths filled with water.
     Now, Michel and his colleagues have found that mudskippers use their mouthfuls of water "like a tongue to capture and swallow food on land, a finding that may give us a glimpse into how the very first land vertebrates evolved from fish 400 million to 350 million years ago," Michel told Live Science.
     The researchers experimented with five mudskippers from Nigeria, using high-speed video cameras and X-ray scanners to record the fish feeding on shrimp.
     Results showed that the mudskippers fed by first exuding water from their mouths and then quickly sucking it back up once it submerged the food. Essentially, the water acted like a tongue.
     When using this "hydrodynamic tongue," the mudskippers moved their hyoids upward, "more or less the opposite of what fish do to feed underwater," Michel said. However, the mudskipper hyoids behaved much like how those of primitive tetrapods such as newts do during feeding.
     The researchers suggest that early tetrapods may have used hydrodynamic tongues when first moving onto land, and evolved fleshy tongues later to gain further independence from the water.
     Michel and his colleaguesdetailed their findings online March 18 in the journal Proceedings of the Royal Society B.

 Excavation on Earth sometimes uses explosives to break up rock or densely-compacted soil. This can be less expensive than using a drill bit or other grinding or impact tools if the explosive is cheaper than the cost of wear on the drill.

 On Mars, drilling and grinding tools shipped from Earth are enormously expensive. They could be made from local materials, but not easily and not as an automated process without significant advances. Explosives are in the same boat; anything shipped from Earth is super expensive. Nitrogen is about 1% of the Martian atmosphere, but in a form that requires substantial chemical processing. (Nearly all industrial explosives use chemicals with nitrogen bonds as the source of their explosive power).

 One resource that is plentiful is carbon dioxide, CO₂. This can be collected directly from the atmosphere and frozen into dry ice pellets. The expansion ratio of CO₂ is 845 (1 cc of dry ice forms 845 cc of CO₂ gas at standard conditions). A small drill or punch can be used to bore a hole into the work face; CO₂ pellets are pushed into the hole and a metal rod with a heater on the end plugs the hole. Heat is applied, sublimating the dry ice into gas and building up a lot of pressure quickly. Used properly, this will cause the surrounding soil to lose cohesion and fragment into clods.

 I don't think this would work well on solid rock but it could be very effective on hardpan or other tightly-packed soils where a grinder or impact tool would endure a lot of wear. This could be useful in particular for excavating a habitat shelter; if the equipment can excavate to bedrock using CO₂ fracturing and simple bucket or augur tools then the required mass, power and spares can be minimized. Another place where it could be useful is if the surface soil layers hold less water than expected for ISRU operations. Surface soils are loose and easily scooped up with a blade or bucket, so the harvesting equipment will be minimal. Adding a CO₂ system like this as a contingency would allow the harvesters to dig deeper and break up ice-bearing soils without requiring any heavy equipment. The force of CO₂ expansion should be strong enough to break up solid ice as well, so if a solid layer of ice is encountered it would be valuable rather than difficult.

 An expanded use for this might be as a drilling rig using gaseous CO₂ as the working fluid, similar to the way shallow wells on Earth can be drilled using water and simple tools. If any soils too dense to be carried away by the gas are encountered they can be fractured by gas expansion; the equipment could be designed to do this without needing to back out the drilling pipe (one-way valve at the end strong enough to survive the gas expansion. If actual solid rock is encountered then a small amount of water can be pumped into the well and frozen at depth, using the expansion of ice to fracture the material. This would be a much slower process but considerably more powerful. This type of drilling is different from taking core samples; it would be intended to reach water ice to be melted and pumped out just like a well on Earth.

 Presumably the same mechanism could be used in outer planet probes using methane ice (melts at 90.7 K, boils at 111.7 K) or nitrogen ice (melts at 63.2 K, boils at 77.4 K) depending on local average temperatures. These two don't sublimate but would have to be heated through a liquid phase; still, the temperature rise required is only 21 K for methane and 14 K for nitrogen. Probes to moons beyond Jupiter and to Kuiper belt objects might use this as a lightweight method of digging shallow craters and collecting subsurface samples for analysis, using heat from an RTG directly as the power source.

 Another way to accomplish the same thing might be simply to use a laser to deliver a pulse of heat to the end of the hole, causing any volatiles to vaporize and expand vigorously. This would require a material sturdy enough to contain the gases while being transparent to the laser, and would require soil with enough trapped volatiles to produce a useful force. It would also need a fair amount of power for the laser.

• 

• 

• 

Long ago we (Larry Niven and Jerry Pournelle) acquired a commercial model called “The Explorer Ship Leif Ericson,” a plastic spaceship of intriguing design. It is shaped something like a flattened pint whiskey bottle with a long neck. The “Leif Ericson,” alas, was killed by general lack of interest in spacecraft by model buyers; a ghost of it is still marketed in hideous glow-in-the-dark color as some kind of flying saucer.

It’s often easier to take a detailed construct and work within its limits than it is to have too much flexibility. For fun we tried to make the Leif Ericson work as a model for an Empire naval vessel. The exercise proved instructive.

First, the model is of a big ship, and is of the wrong shape ever to be carried aboard another vessel. Second, it had fins, only useful for atmosphere flight: what purpose would be served in having atmosphere capabilities on a large ship?

This dictated the class of ship: it must be a cruiser or battlecruiser. Battleships and dreadnaughts wouldn’t ever land, and would be cylindrical or spherical to reduce surface area. Our ship was too large to be a destroyer (an expendable ship almost never employed on missions except as part of a flotilla). Cruisers and battlecruisers can be sent on independent missions.

MacArthur, a General Class Battlecruiser, began to emerge. She can enter atmosphere, but rarely does so, except when long independent assignments force her to seek fuel on her own. She can do this in either of two ways: go to a supply source, or fly into the hydrogen-rich atmosphere of a gas giant and scoop. There were scoops on the model, as it happens.

She has a large pair of doors in her hull, and a spacious compartment inside: obviously a hangar deck for carrying auxiliary craft. Hangar deck is also the only large compartment in her, and therefore would be the normal place of assembly for the crew when she isn’t under battle conditions.

The tower on the model looked useless, and was almost ignored, until it occurred to us that on long missions not under acceleration it would be useful to have a high-gravity area. The ship is a bit thin to have much gravity in the “neck” without spinning her far more rapidly than you’d like; but with the tower, the forward area gets normal gravity without excessive spin rates.

And on, and so forth. In the novel, Lenin was designed from scratch; and of course we did have to make some modifications in Leif Ericson before she could become INSS MacArthur (from novel The Mote in God's Eye); but it’s surprising just how much detail you can work up through having to live with the limits of a model.

---

ed note: so please follow my line of reasoning here.

The Galactic Cruiser Leif Ericson was originally a plastic model that came out in 1968.

Larry Niven and Jerry Pournelle got a Leif Ericson plastic model. They examined it and tried to design a spacecraft based on it, the INSS MacArthur. The MacArthur was streamlined and had scoops. This meant it was a Cruiser class, capable of independent operations. If need be, it could harvest hydrogen fuel by scooping the atmosphere of a nearby gas giant. In other words: In-situ Resource Utilization.

In 1974 Niven and Pournelle wrote the science fiction classic The Mote in God's Eye. It featured the INSS MacArthur.

Marc Miller read The Mote in God's Eye. He thought the fuel scooping ability of the MacArthur was a good idea. So when he wrote the Traveller RPG in 1977, he put that into the game under the term "wilderness refueling."

So what I am telling all you fans of the Traveller RPG is the reason there is wilderness refueling in Traveller is because of the plastic model Leif Ericson!

• 

      The Pax Astra Royal Navy frigate Intrepid falls toward Saturn, inexorably drawn into the planet’s gravity well as the vessel continues its long deceleration burn.

     Sixty meters in length, Intrepid is relatively small for a ship with a maximum range of nine a.u.’s. Designed for military missions rather than exploration or trade, few accommodations have been made for passengers and none for freight, other than the two missile pods slung on either side of its forward hull and the manta-like shuttle moored beneath its wasp-waisted midsection. Imagine a half-liter bottle—the payload module—with its spout glued to that of a three-quarter liter bottle—the engine module—and you essentially have the warship’s architecture.

     Mounted beneath the forward module is a large round aerobrake shield (used for wilderness refueling). Its ceramic tiles, each a different color, have been carefully arranged so that they form the warship’s figurehead: an angel with a sword, her wings spread wide as if flying through space.

     Intrepid’s nuclear-pulse main engine has fired continually ever since the ship left the Moon two hundred and seventy-five standard days ago, its lasers fissioning the deuterium pellets constantly fed into the reactor chamber, causing the uninterrupted string of tiny nuclear explosions which gradually accelerated the ship, at the end of its boost phase, to nearly one-tenth light speed. As Intrepid passed through Jupiter’s orbit one hundred and sixty-eight days ago (i.e., at the journey midpoint), its crew flipped the ship around until its bell-shaped engine nozzle was pointed in the direction of flight. Ever since then, the ship has been applying the brakes as a long prelude to entering Saturnine space (a Brachistochrone trajectory).

(ed note: the Intrepid arrives at Saturn)

     “Very well.” (Captain) Kinnard loosens his seat straps as he rotates it to face the bow windows. “Isidore, initiate rollover maneuver. Jon, finalize trajectories for Saturn atmospheric refueling and Titan rendezvous. Cayenne, ship status?”

     Kinnard punches up the course that Jon has laid in. Studying it, he absently smiles, satisfied that the navigator has done his job. Intrepid arrived at Saturn with its fuel tanks nearly depleted; this was a necessary sacrifice for the constant thrust that approached one-gee when the ship began its midcourse deceleration. However, the frigate was specifically designed for refueling by an aerobraking maneuver through the planet’s upper atmosphere, during which gaseous helium-three would be scooped from the thin stratospheric layer high above its swirling cloudtops. This raw fuel source was less efficient than deuterium pellets extracted and refined from the Moon’s regolith, but it was enough to get Intrepid back home. Indeed, his crew had safely performed much the same maneuver during the Callisto mission two years ago.

     Jon has laid in a trajectory that would graze the top of Saturn’s atmosphere below its rings. Before Intrepid made its refueling run, it would drop off its shuttle, Excalibur, near Titan. By the time he and his crew were viewing the rings of Saturn from below, the landing party would be on Titan’s icy surface, trying to discover why all contact had been lost with Huygens Base and the Hershel Explorer.

(ed note: The captain briefs the crew. Apparently Huygens Base and the Hershel Explorer were attacked by some hostile group and utterly wiped out. For all they know the "hostile group" could be invading aliens. Upon learning this, Lt. Col. DeSoto, leader of Bravo Squad and tasked with the landing party, has a problem with the mission plan )

     (DeSoto says) “As it stands now, you intend to drop my people on Titan before proceeding to Saturn. I understand the reasons for doing it this way. You need to refuel as soon as possible.”

     (Captain Kinnard says) “But you have a problem with it.”

     “From Titan flyby to return rendezvous with Excalibur, there is a twenty-six-hour stretch. That’s the time, at bare minimum, that’s required for Intrepid to make its run and meet up with the shuttle. During that period my team will be on Titan, with no backup from orbit.”

     Kinnard frowns. “Excalibur is outfitted for a two-week stay, if necessary.”

     “In terms of basic life-support, sure. But the shuttle is not equipped with its own weaponry. Given the presumption…” DeSoto hesitates, then corrects herself. “Given the likelihood that there are no survivors at Huygens Base, I consider it imprudent for Intrepid to be so distant from Titan.”

     Kinnard absently caresses his chin with his forefinger. She has a point. Once Intrepid goes deeper into Saturn’s magnetosphere, radio contact with the landing party would become progressively difficult, finally impossible as the ship goes around the planet’s far side. If Bravo Squad ran into problems, it could be several hours before Intrepid found out, and even longer before it could respond. More to the point, though, Intrepid also carries two orbit-to-surface missiles. If there is trouble on the surface, Bravo Squad can call in a space-strike as a last resort.

     And without a doubt, there’s something hostile on the Galileo Planitia. Leaving eight men and women down there—however well-armed and trained they may be—could be a fatal risk.

     Isidore is already recalculating Intrepid’s course on his wristcomp. (Captain Kinnard says) “Jefe, can we adjust the trajectory to put us in orbit around Titan?”

     Kinnard considers it for a moment. “Okay,” he says, “go topside and tell Jon to lay it in. We’ll do the run after we get Excalibur back aboard. Tell Marie to alert FLTCOM of the change.”

The purpose of my first post on this topic was simply to run some numbers and see how long starship refueling takes and how large starship squadrons might go about it. I found that the minimum specifications for squadron (10% total tankage on partially streamlined tankers or tenders capable of gas giant fuel scooping) refueling were a little silly. But now that we had a time frame we could extrapolate for squadrons with more and better tenders. I also mentioned that refueling took several days per Trillion Credit Squadron and brought up the problem of SDBs lurking in a gas giant (almost as beloved a trope as starfighters).

Then Klaus Teufel brought this up:

KLAUS TEUFEL:
I think System Defense Boats (SDBs) couldn't effectively ambush refuelers unless the SDBs were really lucky, or there are a lot of refuelers. Jovians are big, and even Traveller atmospheric speeds have limits. SDBs probably live in low polar orbit, rather than atmosphere; dipping in when fuel is low.

Let's crunch some numbers.

Jupiter has an area of 52 billion square kilometers. A fast streamlined starship, let's say it makes Mach 5. If refueling takes 6 hours as I suggested the SDB can intercept starships passing within 36,000 km. That gives an area of 400 million square kilometers or 0.7% of the planet's area. That means you need at least 130 SDBs to cover a gas giant. That's for an intercept by one SBD which is a tall order for the SDB if the opposing task force has any kind of admiral in command. The tenders will either have defenses or escorts (hey, fighters might be a good idea after all!)

If the SDBs are any good at all we're talking 200 mega-credits (Mcr) each, that means you need 26 billion credits for minimum coverage. If you use ten times the number to have a SDB flotilla covering the gas giant completely that 260 billion credits. Ten ships probably won't be enough. Remember the name of the game is High Guard. The rest of the invading starship squadron will be hovering nearby ready to call the wrath of GHU down on your SDB flotilla. Now 260 billion credits is also a lot to spend on a last ditch scorched earth strategy. Maybe if you spent that money on your main fleet the bad guys wouldn't win in the first place? Most planets haven't got many trillions to spend on defense. Likewise most sector navies don't want to spend that much on every planet.

So how do you defend your gas giant?

In a word: nukes.

Read Special Supplement 4: Missiles. Mines are perfectly allowable in that system and fairly cheap. In space even an unguided piece of explosive will hit anything within 2,500 miles. So they must still have some kind of short range guidance and propulsion. Buy a bunch of them. Stick them under balloons. They have an intercept area of 20 million square kilometers and you need 2,600 to cover a gas giant. At the cost of even 100,000 cr. you could buy a few thousand for the cost of a single SDB. Seed the gas giant with them. Use your SDBs to maintain and control them as needed. When the bad guys show up watch hilarity ensue.

Even if an invading starship is moving mach 1 to refuel it cover 24,000 kilometers in the six hours I established for refueling. That means it cut across the engagement areas of at least ten nukes. Even that relatively expensive option is probably only 10 Mcr or less. Again the defender can afford 10 times or more the number of turrets as SDBs.There will probably be more. Instead of a single mine laying under a balloon imagine a remote controlled triple turret with three launchers and a missile magazine.

May I point that nukes are bad in space but they are absolutely terrifying in an atmosphere. In space nuclear weapons mainly damage through x-rays melting your hull. Atmospheres add blast effects to that. This is happening to a tanker starshp or tender starship the owner probably try to save money on. The tanker is probably moving at several Mach. It will not respond well to huge blasts being set off around it.

I always assumed the invading High Guard concerned themselves with incoming attacks while their comrades were refueling. It seems they need to worry about what is below as well as above. Refueling might be a matter of clearing a region of the gas giant and confining your refueling operations there. But by then you've restricted your area of operations and then the defending SDBs have a great chance to find you and raise merry hell.

I said it before but Traveller is about making difficult decisions. Personally I'd chicken out and refuel at the nearest Europa type moon. Quick thaw an area with nukes or lasers and fill them up (starships can easily crack water into fuel and oxygen).

Except you could mine Europa too.

• 

• 

• 

Mark Fogg

Upon reentry, the airframe has to asborb all the energy that was used in lofting that ship into orbit. So, my scoop ships are diving from high above a Jupiter, heating up in the atmosphere, and ramming all the free fuel into storage tanks. Heat of entry the airframe absorbs, just like a shuttle reentry. Heat of compression? Man, has anybody thought of that? I could see some kind of heat exchangers mounted in delta wings or some such, but you gotta dump a vast amount of heat real quickly or your onboard storage tanks become bombs. None of the online wilderness refueling site discussions seem to cover that.

I work in the oil and gas industry, so I know how it's done in a static installation, but aboard a large aerospace craft making a kamikaze run into a turbulent atmosphere is a whole 'nother set of problems.

---

Winchell Chung (me)

The question is above my pay grade. Just winging it I'd say a possibility is using extreme open-cycle cooling.

Some of the scooped gas will have to be sacrificed, turned into a heat sink that is then instantly blown out the tail pipe to get rid of the compression heat.

---

Rob Davidoff

The issue is open-cycle means you may be dumping more coolant than you're taking in. Fancy cooling is a lot of the "secret sauce" in Skylon's SABRE engines—using the liquid hydrogen coming out of the fuel tanks as a sump for the heat of compression created in the "intake/compressor" portion of the engine, which is fine since that same LH2 is bound for an engine where it'll be heated into a gas by combustion anyway.

The issue is that here, you don't have that energy sump., and heat exchangers could easily be saturated by the aerodynamic heating around the ship. I wonder if you might be better off with a system that stays out of the main atmosphere and dangles a winged collector on a rope/pipe down into the air proper. The self supporting length for carbon fiber is 250 km—plenty to be into pretty near-vacuum conditions for the main ship while the collector reeling out below it is into the depths. You can pump the gasses up the "reel" and compress and store at the top, where you get a better radiator performance, and because you're not trying to store as much as you can on one "dive" but instead are operating statically, you don't need the same throughput of gas, reducing the heat pulse to a smaller, more measurable heat rejection rate.

---

Alistair Young

Hm. From the not-yet-even-back-enveloped-this files, seems to me like you're going to have plenty of stuff to throw away anyway in this operation (at least in my universe, they're mostly gas mining for ²H and ³He, which I expect to involve dumping lots of ¹H and ⁴He).

So, hypothetically, could we use one of the assorted heat pump techniques to transfer heat from the fraction we're keeping into the tailings before dumping them over the side? Even though running that would generate more heat, it might still be overall negative.

---

Rob Davidoff

Alistair Young, on a similar level of rigor, you don't have a very long window to do all this, so in order to even do that you'd need to be pulling the 2H from the 1H and the 3He from the 4He, then dump the appropriate heat into the appropriate pipe (one to the tanks with its compressors, and then you run the tailings outside that and overboard). Spiking the atmosphere at Mach 20 or something, you don't have a lot of time to do all that.

I think you'd really have to just cast a wide net, grab what you can, and sort it out back in orbit. The basic "dump the heat into the tailings' concept, taken to extremes, becomes the "convection heat exchanges all along the wings" routine.

---

Constantine Thomas

I don't think scooping actually works as it is commonly imagined — you can't just open up some shutters and suck in stuff while you're zooming through the atmosphere at high velocity — unless you want to use it for a ramjet or scramjet. If you tried that I think the stresses (among other things) would tear the ship apart.

I think the only way that fuel scooping could work without destroying the ship is if you can literally hover in place and suck stuff in.

So it looks like the general point is this: if you need to scoop, do it where the atmosphere is VERY rarefied. Zooming through the cloud decks with your scoops open is just suicide.

---

Isaac Kuo

There are a number of issues going on here. First off, you ultimately get rid of the heat with radiative cooling. This might be done in a steady state, as in PROFAC, or it could be done along with periodic dipping into the upper atmosphere (elliptical orbit). In the latter case, you can use a "block of ice" to absorb some heat, while melting, during the brief atmospheric passes.

Either way, compression heating is going to mean mining Jupiter is going to look pretty bad compared to mining Uranus. The kinetic energy per kg is proportional to the square of the escape velocity—that means dealing with 9 times the energy in compression heating! It also means pumping 9 times the energy to maintain orbit, and 9 times the energy to get the hydrogen out of the gravity well.

And in any case, mining any gas giant's atmosphere looks pretty bad compared to ice mining small bodies. I'm actually a big fan of atmospheric scooping for mining, but the deep gravity wells involved make it look pretty bad for the ones available here in our solar system.

But assuming you want to do hydrogen atmospheric scooping of gas giants, PROFAC tells you basically what's required. You need some sort of high Isp propulsion to counteract drag. You need a conical scoop to accept thin atmosphere. You need a compressor at the base of the scoop so the gas actually gets "sucked" in rather than just bouncing away. You need to dump the heat of the hot collected gas. While PROFAC ultimately created cryogenic oxygen, that may not be practical for hydrogen. It may be easier to store the hydrogen by chemically binding it to on board carbon.

The most important and counterintuitive thing to know is that the ram pressure of the cone does NOTHING to help you collect the gas. Without the compressor, the pressure will equalize with the (nearly zero) ambient pressure.

• 

• 

---

Alistair Young

I'm much more inclined to the balloon trick for industrial-scale gas mining, myself, with later advancement to the partial orbital elevator used as a giant straw.

(ed note: the "balloon trick" is to place a gas harvesting unit in the atmosphere suspended by a nuclear-powered hot-air balloon. It gradually accumulates the desired gas, and is periodically visited by tanker rockets. Best for gas giants Saturn-sized and under, otherwise the delta-V for the tanker is uneconomical.

• 

• 

"Yes, we are pretty isolated," he said. "The Jupiter ships just unload their balloons, pick up the empties, and head right back for another cargo."

"I don't understand how you can found an industry here, when your raw materials only arrive at conjunction," Ellen said.

"Things will be different once we're in full operation," Blades assured her. "Then we'll be doing enough business to pay for a steady input, transshipped from whatever depot is nearest Jupiter at any given time."

"You've actually built this simply to process ... gas?" Gilbertson interposed. Blades didn't know whether he was being sarcastic or asking a genuine question. It was astonishing how ignorant Earthsiders, even space-traveling Earthsiders, often were about such matters.

"Jovian gas is rich stuff," he explained. "Chiefly hydrogen and helium, of course; but the scoopships separate out most of that during a pickup. The rest is ammonia, water, methane, a dozen important organics, including some of the damn—doggonedest metallic complexes you ever heard of. We need them as the basis of a chemosynthetic industry, which we need for survival, which we need if we're to get the minerals that were the reason for colonizing the Belt in the first place." He waved his hand at the sky. "When we really get going, we'll attract settlement. This asteroid has companions, waiting for people to come and mine them. Home-ships and orbital stations will be built. In ten years there'll be quite a little city clustered around the Sword."

---

As they glided through the refining and synthesizing section, which filled the broad half of the asteroid, the noise of pumps and regulators rose until it throbbed in their bones. Ellen gestured at one of the pipes that crossed the corridor overhead. "Do you really handle that big a volume at a time?" she asked above the racket.

"No," he said. "Didn't I explain before? The pipe's thick because it's so heavily armored."

"I'm glad you don't use that dreadful word 'cladded.' But why the armor? High pressure?"

"Partly. Also, there's an inertrans lining. Jupiter gas is hellishly reactive at room temperature. The metallic complexes especially; but think what a witch's brew the stuff is in every respect. Once it's been refined, of course, we have less trouble. That particular pipe is carrying it raw."

They left the noise behind and passed on to the approach control dome at the receptor end. The two men on duty glanced up and immediately went back to their instruments. Radio voices were staccato in the air. Blades led Ellen to an observation port.

She drew a sharp breath. Outside, the broken ground fell away to space and stars. The ovoid that was the ship hung against them, lit by the hidden sun, a giant even at her distance but dwarfed by the balloon she towed. As that bubble tried ponderously to rotate, rainbow gleams ran across it, hiding and then revealing the constellations. Here, on the asteroid's axis, there was no weight, and one moved with underwater smoothness, as if disembodied- "Oh, a fairytale," Ellen sighed.

Four sparks flashed out of the boat blisters along the ship's hull. "Scoopships," Blades told her. "They haul the cargo in, being so much more maneuverable. Actually, though, the mother vessel is going to park her load in orbit, while those boys bring in another one—see, there it comes into sight. We still haven't got the capacity to keep up with our deliveries."

"How many are there? Scoopships, that is."

"Twenty, but you don't need more than four for this job. They've got terrific power. Have to, if they're to dive from orbit down into the Jovian atmosphere, ram themselves full of gas, and come back. There they go."

The Pallas Castle was wrestling the great sphere she had hauled from Jupiter into a stable path computed by Central Control. Meanwhile, the scoopships, small only by comparison with her, locked onto the other balloon as it drifted close. Energy poured into their drive fields. Spiraling downward, transparent globe and four laboring spacecraft vanished behind the horizon. The Pallas completed her own task, disengaged her towbars, and dropped from view, headed for the dock.

The second balloon rose again, like a huge glass moon on the opposite side of the Sword. Still it grew in Ellen's eyes, kilometer by kilometer of approach. So much mass wasn't easily handled, but the braking curve looked disdainfully smooth. Presently she could make out the scoopships in detail, elongated teardrops with the intake gates yawning in the blunt forward end, cockpit canopies raised very slightly above.

Instructions rattled from the men in the dome. The balloon veered clumsily toward the one free receptor. A derricklike structure released one end of a cable, which streamed skyward. Things that Ellen couldn't quite follow in this tricky light were done by the four tugs, mechanisms of their own extended to make their tow fast to the cable.

They did not cast loose at once, but continued to drag a little, easing the impact of centrifugal force. Nonetheless, a slight shudder went through the dome as slack was taken up. Then the job was over. The scoopships let go and flitted off to join their mother vessel. The balloon was winched inward. Spacesuited men moved close, preparing to couple valves together.

"And eventually," Blades said into the abrupt quietness, "that cargo will become food, fabric, vitryl, plastiboard, reagents, fuels, a hundred different things. That's what we're here for."

• 

• 

"You are the captain of the mother ship." Pearson said. "However, we're in orbit now. Only the scoopships are under weigh. And I direct their operations. Under the laws of the (Asteroid) Republic, they're my responsibility. You'll find working for the Jupiter Company is a lot different from an inner-planet merchant run."

---

"They aren't ordered," Pearson reminded him. "Any pilot may refuse any flit. Of course, if he does it repeatedly, he'll be fired—We can't afford to ship deadheads."

"I know, I know. And yet, well, you asterites are obsessed with economics." The captain lifted a hand to forestall the manager's retort. "I am quite aware of how closely you must figure costs. But there's a ... a callousness in your attitude. You often seem to think a machine is worth more than a human life."

"It is, if several other human lives depend on it."

---

"And it isn't necessary. You could automate the operation."

"Doubling the capital investment in every scoopship," Pearson said. "Also increasing the rate of loss by an estimated twenty-five percent. Too many unforeseeable things can go wrong down there. An autopilot can act only within the limits of its programming. A man can do more. Sometimes, when he runs into trouble, he can bring his ship back."

---

"Clear track," said the dispatcher's radio voice. Static buzzed around the words. No tricks of modulation could entirely screen out the interference of Jovian electrical storms. "Good gathering, Tom."

"Roger," said Hashimoto, mechanical response to a ritual farewell, "thanks, and out." His eyes focused on instrument needles, his fingers jumped over switches. The computer clicked and muttered. Otherwise the cockpit was silent, making the beat of blood loud in his ears. He grew conscious of the spacesuit enclosing him, a thick rubbery grip. Its helmet was left off, like its gloves, until such time as an emergency arose. So his nostrils drank smells of machine oil and the ozone tinge that recycled air always has in close quarters. For the minute or two that he traveled in free fall he felt weightlessness: scoopships didn't waste mass on internal field generators. But there was no dreamlike ease to the sensation, such as he had known in other days. The seat harness held him too tightly.

The computer gave him his vectors and he applied power. The nuclear reactor aft was noiseless, but the Emetts of the gyrogravitic generators whirred loudly enough to be heard through the radiation bulkhead which sealed off the engine compartment. Field drive clutched at that fabric of relationships that men call space. Acceleration shoved Hashimoto back into his seat. Maij Girl leaped Jupiterward.

He had a while, then, to sit and think. This interval of approach under autopilot was the worst time. Later the battle with the atmosphere would occupy all of him, and still later there would be the camaraderie of shipboard. But now he could only watch Jupiter grow until it filled the sky. Until it became the sky.

The trouble is, he realized, I'm so near the end of my hitch. I didn 't count the days and the separate missions at first, when I began this job. But now that there's only a few more months to go....

Three years!

He hadn't needed to stay in the Belt that long, as far as his wife was concerned. She wanted desperately to have children, yes, and her frail body would miscarry again and again unless she spent each pregnancy under next-to-zero weight, and obstetrical facilities for that kind of condition existed nowhere but in the Asteroid Republic. (No country on Earth would spend money to establish a geegeeequipped maternity hospital, or an orbital one; anything that increased population, however minutely, was too unpopular these days.) Hashimoto had been more than glad to land a contract with JupeCo that enabled them to move out here. But two healthy children were plenty. Now they wanted to return home.

However, JupeCo insisted on a minimum of three years' service, and the bonus he would lose by quitting before the term was over amounted to half his total pay. He couldn't afford it. No contract that harsh would have been allowable in North America. But once they concluded their war of independence, the asterites had gone their own way. The asterites were as raw and stark as their own flying mountains.

---

The scoopship thrummed around him. Through the low, thick inertrans canopy he looked forward along the flaring nose. By twisting his neck he could have looked aft to the tapered stern. The metal shimmered blue in the light that poured from Jupiter. He could not see that open mouth which was the bow, gaping upon emptiness, but he could well visualize it. He had watched the service crew often enough, to make sure that their periodic inspections of every accessible part were thorough.

And by the Lord Harry, it was something to steal from Jupiter himself and come back to brag about it!

Eventually the planet filled his entire vision. But then it was no more a planet, hanging in heaven; it had become the world. It was not ahead but below. Cloudfields stretched limitless underneath him, layered, seething, golden-hued but streaked with the reds and browns, greens and blues of free radicals. To port he saw a continent-sized blot of darkness that was a storm, and shifted course. Deceleration tugged angrily at him, and the planet's own pull, nearly three times Earth's. His muscles fought back. The first thin keening of cloven air penetrated to him. The ship quivered.

He switched off the autopilot and plunged downward on manual. The noise grew until it was thunder, booming and banging, rattling his teeth in the jaws and his brain in the skull. Winds did not buffet this craft traveling at many times supersonic speed, but gigantic air pockets did, back and forth, up and down, till metal groaned. Darkness overwhelmed him as he passed through a cloud bank. He emerged below it, looked up and saw the masses towering kilometer upon kilometer overhead, mountainous, lightning leaping across blue-black cavern mouths and down the faces of roiling slaty cliffs, against a distant sky that was hell-red. Briefly an ammonia storm pelted him, the hull drummed with the blows of gigantic poisonous hailstones. Then he was past, still screaming downward.

Presently he was too deep for sunlight to touch his eyes. He flew through a darkness that howled. He ceased to be Tom Hashimoto, husband, father, North American citizen, registered Conservative, tennis player, beer drinker, cigarette smoker, detective-story fan, any human identity. He and the ship were one, robbing a world that hit back.

The instruments, lanterns in utter murk, told him he was at sufficient depth. He leveled off and snapped the intake gate switch. The atmosphere ceased to whistle through the open tube of the hull—for now the tube was closed at the rear. A shock of impact strained him against his harness. The ship bucked and snarled. He reduced the drive to let the atmosphere brake him.

That air was mostly hydrogen and helium, but rich in methane, ammonia, carbon dioxide, water vapor; less full of ethylene, benzene, formaldehyde, and a dozen other organics, but nonetheless offering them in abundance. This far down, none of them were frozen out. The greenhouse effect operated. Jupiter's surface was warm enough to have oceans like Earth's. No man had seen them. The weight of atmosphere would have crumpled any hull like tinfoil. Even at this altitude, Mary Girl sped through an air pressure several times that of sea-level Earth.

Rammed into her open bow by sheer speed, the gases poured through a narrower throat. The wind of their passage operated an ionizer and a magnetic separator. Most of the hydrogen and helium were channeled off into a release duct and thrown away aft. Some of the other gases were too, of course, but there was more where they came from. An enriched mixture flowed—hurtled—through rugged check valves into the after tanks.

The process did not take long. This was actually not the time of maximum hazard—though ships had been known to break up when the stress proved too much for some flaw in their metal. The dive downward from orbit had killed most of those who had perished, and the climb back was not always completed. Gales, lightning, hailstorms, supersonics, chemical corrosives, and less well understood traps could be sprung. If the pilot was simply knocked unconscious, or lost control for a couple of minutes, Jupiter ate him.

A needle crossed the Full mark. The intake gate opened again and the tank valves shut. Hashimoto swung the ship's nose toward the hidden sky and poured power into the field drive.

He was once more out in sunlight, a storm-yellow dusk that showed him nothing but a cloud wrack tattered by wind, when his engine began to fail.

---

Pumps throbbed, forcing the scoopship's cargo of Jovian gas into the balloon. The sphere did not expand much; a single load was a small fraction of its total capacity. D'Andilly continued working to balance forces and hold the entire system steady in orbit.

At the end, he directed the hose to uncouple and retract. Then he slipped smoothly toward his assigned blister on the mother ship. This far spaceward there was seldom need to operate hydro-magnetic screens against solar particle radiation, so approach and contact were simple. While he got out of his harness and suit, the final adjustments of angular momentum were made. The balloon waited quietly for the next arrival.

Who would not be d'Andilly. He had twenty hours off till he dove again.

Whistling he climbed through joined air locks into the Vesta Castle. Two maintenance men waited in the companionway to clean his gear. Afterward the ship would be inspected. That was no concern of d'Andilly's. He gave the tech monkeys a greeting less condescending than compassionate—imagine so dreary a job!—and sauntered to pilot's country; a short, stocky man, brown hair carefully waved and mustache carefully trimmed, blue eyes snapping in, a hook-nosed square face.

Ulrich von Raaben, tall, blond, and angular, was emerging from the showers as d'Andilly entered. "Whoof!" he exclaimed. "You smell like an uncleaned brewer's vat." He saw the condition of the undersuit that the Frenchman began to strip off, and paused. "Bad down there?"

"I hit an unobserved storm," d'Andilly said, as casually as he could manage.

Von Raaben stiffened. "We shall have a word with the weather staff about that."

"Oh, I will report the matter, of course. But they cannot be blamed. It must have risen from the depths faster than normal. Our meteorologists can only observe so far down."

"A cyclonic disturbance does not rise for no reason. Surrounding conditions ought to give a clue, at least to the probability of such a thing happening. If they tell us a given region looks calm, and it proves not to be, by heaven, they will have some explanations to make!"

He ducked under the shower and wallowed in an extravagance of hot water. That was one of numerous special privileges enjoyed by the scoopship pilots. Others included private cabins, an exclusive recreation room, seats at the officers' mess with wine if desired, high pay, and a dashing uniform that one was free to modify according to taste. In exchange they made a certain number of dives per Earth-year, into Jupiter.

One must be young and heedless to strike such a bargain. Sensible men, even among the asterites, preferred a better chance of reaching old age. No wonder that scoopship pilots off duty tended to act like ill-disciplined sophomores. Including me, no doubt.

---

Pearson's eyes dropped. He stared for a space at his artificial hand, inert on the table. Finally he said, "But I do know. I was a space pilot once myself. Not scoopships, no, but prospecting, which is pretty dangerous, too, in a rock cluster. Some good friends of mine died in the same collision that shelved me. I managed to get into an intact compartment, alone. But I'd soon have died too, if the survivors hadn't risked their necks to search the debris for casualties.

"But ... that was sound doctrine. The ship was a total loss. Nothing more was being hazarded except men, who'd die in any event if they couldn't pool their efforts to jury-rig sufficient shelter until help came. This case is different. You have to multiply values to be gained or lost by the probability of success or failure. Exposing three ships and three men to a very high chance of destruction, for the sake of one ship and one man whom there's only the smallest likelihood of saving ... no, that's much too bad economics.

"Economics?" d'Andilly exploded.

"That's what I said," Pearson answered. Steel underlay his tone. "The dollar cost of building and outfitting a ship, of training and equipping a man. It's the only basis we've got.

"Wisner, you're an asterite born, and von Raaben has been one for a number of years. But I guess I'll have to spell the facts out for you. Pilot d'Andilly. You're kept like a fighting cock, because that's the only way to attract men to your job. So you aren't aware, I suppose, how thin a margin we asterites live on. Can you imagine what it means to carve a living from airless rocks? Sure, they're rich in metal; atomic power is cheap and solar power is free; but what is there otherwise? Why raid Jupiter at such enormous effort, if we didn't have to have those gases to form the basis of chemical synthesis, of our whole chemical industry, which equals our survival?

"Okay. It's barely possible that three ships working together could grapple onto Hashimoto's and haul him into clear space. I don't believe they could, but I'll grant a slight possibility. So if you did pull off that stunt, every boy on every asteroid would cheer himself hoarse for you, and every girl would fall into your arms, and every man would curse you for a pack of dangerous idiots. Because any operation which consistently gambled at those odds would soon go broke—and we've got to have the operation or the whole Republic dies.

"Now do you understand?"

• 

• 

ed note: The Traveller RPG uses wilderness refueling from gas giants extensively. Rob Garitta point out the many reasons why this seemingly simple operation is actually fraught with peril.

A "system defense boat" (SDB) is a combat spacecraft with no FTL drive. Which means the mass a combat starship uses for the FTL drive is in the SDB devoted to more weapons and defenses. Kilogram for kilogram a SDB outguns a combat starship of the same mass.

Traveller FTL has the "jump limit": you must move away from the planet a distance of 100 planetary diameters before using FTL or Something Awful happens to the starship.

---

Wilderness Refueling, Local gas giant

A. Achieve orbit

This may not be as simple as it sounds. You must be prepared to deal with:

• Debris from rings
• (Electromagnetic) radiation
• Particle radiation

The orbit will be near the cloud tops. A trip out to the jump limit is 5 to 10 million klicks and will take several hours for a ship that makes 3 gees. This is of concern to Navy operations and anyone else afraid of an attack deep in a (gravity) well (it will be several hours before) they can fall back (outside the jump limit and) call on the Jump Fairy to get them out of a tight spot. You could have part of your squadron at the jump limit and let only the ships needing refueling enter a close orbit and retreat to the jump limit when done.

Of course any (enemy) System Defense Boats (SDBs) waiting in the gas giant are waiting for you to split your forces.

(Defender) SDBs have it relatively easy. They aren't in a hurry to be somewhere else. They can loiter in relatively calm regions of the gas giant's atmosphere. They can pump in hydrogen as they need it for their power plants. Traders and interested others are trying to get fueled and get out fast and are bound to make mistakes.

B. Refuel

Great you made it this far! Be prepared to deal with:

• Downdrafts
• Life forms: gas giants do not usually produce intelligent life. Traveller canon does mention one race. Be careful you don't suck someone important into your fuel tanks. Beware the referee who reads H.P. Lovecraft.
• Contaminated fuel: the good thing about contaminants in fuel is that you can usually smell them. That ammonia leak might cause concern but it also indicates your fuel tank has a leak.
• Lightning strikes: lightning strikes are the natural enemies of starships.
• Diamond storms: theory holds that Jupiter and other gas giants have carbon cores that under incredible pressure become diamond. Convection might throw diamond bits into the upper atmosphere. The bad news — this can damage or wreck your ship. The good news — the diamonds are probably poor quality so you don't need to worry about destabilizing the gem market.
• Communications going out: they will at some point.
• Sensor blindspot: probably near where the comms go offline.
• SDBs: yet again.
• Pirates: sauce for the goose, my friends.

I have no idea what kind of target numbers you need to roll to avoid damage or maintain control. I'd set them at 10+ and make the damage of concern but not immediately fatal.

Keep in mind many people skimp on armament for their fuel tenders. In this case a 600 ton SDB might immobilize a 100,000 ton dreadnought by taking out its fuel tenders to deny it fuel.

C. Set course to major world or outsystem

Yes. Please.

Note that this sort of piloting can be stressful and tiring to pilots. A 24/7 fueling operation might see pilots being rotated between the tenders and the fleet or they might be willing to let their tenders make mistakes while docking our handling cryogenic and inflammable materials.

Some gas giants will have orbiting weather satellites to help ships chart safe courses to refuel. Usually these are not found at C starports who want to sell you their rotten contaminated fuel. If the system has an A or B starport, a Navy or Scout base they have satellites orbiting the nearer gas giant.

Weather satellites could also keep a record of ships refueling or be part of a defense system (mines).

[L]ife can multiply until all the phosphorus is gone, and then there is an inexorable halt which nothing can prevent,” he wrote. “We may be able to substitute nuclear power for coal, and plastics for wood, and yeast for meat, and friendliness for isolation—but for phosphorus there is neither substitute nor replacement.

Sevoris Doe:

     So, we recently came about reviewing Phosphor Supplies in Space over on the ToughSF Discord, and the math looks interesting.
     It has been proposed that space colonies may run out of phosphorus for farming and thus population support. That… doesn't really work out on detailed observation, though the economics also don't look utterly rosy either.
     Basically, Phosphor is present at about 1 gram/kg of terrestrial crust. For planets and planetoid rubble that can be used as an average assumption. Mind, that is not a lot — phosphorus minerals have much higher concentrations of the stuff — but ultimately it is very workable. Here's why.
     An adult person needs about 700mg of Phosphor per day. At 1g/kg of phosphor concentration, supplying enough phosphor for 250,000 people requires you to grind down and chemically process all of 176.1 tones of rock. That's for a day so let's escalate that number. For three months worth of buffer in a closed-loop life support system we'll need to processs 15,849 tones of rock.
     But that is still not a lot. And I would argue that you will process many more times in rock, metaloid silicates etc. trying to get why you are in space, which is to say: thousands of tones of rare metals, millions of tones of metallic and silicate construction materials and equal amounts of volatiles, and it is attractive to lump these together. Washing out phosphorus also washes out other elements you want to get rid off, so it's basically a processing byproduct.
     In my conclusion, a space colony will not run out of phosphorus any time soon. They'll need closed-loop life support — but that is basic operation procedure for a space colony. Depending on how autonomous and self-replicating your mining operation is, you might get to the point where you're throwing away the sulphuric acid… though this doesn't pay after a point; acids used for ore processing is expensive once you go about using it in large amounts, you'll want to reclaim it.
     Mass-wise, every other bit of population-support infrastructure will be more expensive. You'll be processing more rock for silicate fiber structure materials and radiation shielding for the new habitats; and asteroid rock for metals to make the life support and hydroponics for new people, than in phosphorus. At least if you have a healthy asteroid diet.

G dVille

     Overall, phosphorus is potentially a limiting element for life in the universe. Probably between that and nitrogen. Certainly not water, the staple of many a scifi plot (last century, anyway). For the near term at least, local constraints will govern the expansion of Earth life. Mars has 5 times the available phosphates of Earth, but has a deficit of nitrogen. Meanwhile, Luna seems to be short of carbon.
     My pet project of the last few years is developing a room temperature 3D printable low-temp-cured cement based on phosphate chemistry, as a basis for creating habs on Mars. So even beyond biology, phosphorus may be in demand.
     Also for the world development of a story, I've been looking into chemotrophic ecology. Phosphates play a pretty critical role there in the cellular biochemistry.
     Chemotrophic ecology is probably going to be a cornerstone of ecology construction for any human hab- there has to be a way to replicate the Great Oxegenation Event. Photosynthesis may not be feasible. Inorganic electrolysis probably requires an inorganic power source. Maybe this is the most feasible way to initiate non-photosynthetic oxygenation, but I'm still looking into a bioregenerative method for my story that is not reliant on human maintenance of machinery.

A gentleman named Mr. MJW Nicholas wrote me with a brilliant suggestion. He points out that Terra itself is heading for a phosphorus shortage, "Peak Phosphorus". In that case, instead of Terra having a strangle hold on the space colonies, it might be the other way around. By the same token it would become MacGuffinite.

I was interested to read in the 'Rocketpunk and MacGuffinite' topic the subject of peak oil, and how humanity could make use of Titan. I did a little bit of digging and it struck me how, even if we do come up with viable and sustainable alternatives for both transport and energy production, there are no such alternatives for the vast quantity of other petroleum products our modern society is utterly dependent on.

It was suggested on a number of websites that alternatives for pharmaceuticals would be the holistic or home remedy type eg. willow bark instead of aspirin, and I came to the conclusion that even if you could find natural alternatives, you'd need huge amounts of land to grow them in the quantities required, land which would also need to be used to support cotton and hemp growth to meet the demand for natural fibres for clothing, given that many modern clothes contain oil-based synthetic fibres. Other types of natural fibres come from animals, but then they need grazing land, which means even more land is used. Regardless of the land usage, there is always one thing land will need to be used for — food crops. There is only a finite amount of arable land available, and many breeds of plant can only be grown in certain locations, based on a wide range of environmental variables, which further limits crop yields without either long-term efforts into selectively breeding, or direct manipulation of genes for desired traits. The first one can take potentially hundreds of generations to achieve, depending on the desired result, and the latter requires laboratories, who use equipment that would be difficult and costly to produce, repair or replace in a post-peak oil world, even if one takes into account the usage of oil-sands.

Even if we tapped into difficult to access reserves on a larger scale than we already do, such as deep-sea wells and oil-sands, and even if the ban on exploiting Antarctica's potentially vast mineral wealth was lifted, this is still not a viable long-term solution. Obviously, getting to Titan and extracting, and refining the mineral wealth there in sufficient quantities, and shipping it back, would be immensely costly. I know full well that you know the amount of work and effort behind setting up propellant depots and in-orbit refineries and all the other stuff needed to set that kind of infrastructure in motion, let alone maintain it. This kind of future is one, however, that allows for colonization. But it got me thinking — what are other things that humans, and modern civilisation with it's global scale infrastructure would need, and we have a finite amount of?

Then I harked back to another part of your website, where you mention phosphorus.

Much like peak oil, it is predicted, optimistically, that we'll hit Peak Phosphorus within the next 80-100 years, pessimistic estimates suggest by 2030. Having done some more digging, I noticed that whilst some claim that recycling phosphorus from sewage, and having better crop management and limiting run-off, etc. could outright halt peak phosphorus, a larger number of articles suggested that even with these measures, we're only delaying it. Even if we stop it altogether, we're now limited on how much of anything we can grow, which limits crop yields, which, as you can see, would have a negative impact on the proposed 'plant-based' alternatives for petroleum-based products.

Which leads me onto this — recent in-situ analyses of Martian soil suggest that water soluble phosphorus exists in higher concentrations than anywhere on Earth, with rich deposits near the surface, as well as deeper underground. Also, recent spectroscopic analyses of several near-Earth objects have suggested higher concentrations of phosphorus in C-type asteroids than previously believed.

Both of these things are much easier to get to than Titan, comparatively speaking. Also, given the greater urgency to find alternative phosphorus sources, you could probably convince more people to financially back martian or NEO colonization or exploitation efforts. This would also make it easier to suggest to people 'hey guys, oil's getting a bit pricey, how about Titan?' because you've already got the infrastructure in place between here and Mars.

• 

Phosphorus plays a central role for life on Earth. It is an intimate part of life's architecture, contained in the salts that stiffen vertebrate bones and in phospholipids that form the walls of all living cells. It is linked to life's fundamental fuel, adenosine triphosphate (ATP), the energy storehouse that powers just about every physiological action. Even the lengthy genetic sequences of DNA and RNA — the blueprints for life itself — lie cradled within the twisting embrace of a pair of helical backbones built from phosphorus.

Yet for all its biological importance, the element is in remarkably short supply on Earth. According to recent studies, hydrogen atoms outnumber phosphorus atoms by 49 million to 1 in Earth's oceans, 2.8 million to 1 in the universe at large, and 203 to 1 in bacteria. Phosphorus fares a little better with oxygen atoms, which outnumber it by 25 million to 1 in the oceans, 1,400 to 1 in the cosmos, and 72 to 1 in bacteria. For every atom of phosphorus counted in such a census, carbon and nitrogen atoms appear, respectively, 974 and 633 times more often in the oceans, 680 and 230 times more frequently in the universe, and in numbers 116 and 15 times greater in bacteria.

Even these statistics belie the true importance of phosphorus, which scientists credit as the limiting factor for terrestrial life. This idea follows Justus von Liebig's law of the minimum, an early agricultural concept stating that a species responds only to the nutrient in shortest supply and that this is what limits the growth of a given population. Science popularizer Isaac Asimov, in his 1974 book Asimov on Chemistry, put it most succinctly: "Life can multiply until all the phosphorus has gone and then there is an inexorable halt which nothing can prevent."

So where did Earth's phosphorus come from?

"Because phosphorus is much rarer in the environment than in life, understanding the behavior of phosphorus on the early Earth gives clues to life's orgin," said Matthew Pasek, a doctoral candidate at the University of Arizona's Lunar and Planetary Laboratory. Working with Dante Lauretta, assistant professor of planetary sciences at the university, Pasek argues that iron meteorites could have brought more phosphorus to Earth than occurs naturally. He presented his ideas at the 228th American Chemical Society national meeting in Philadelphia on Tuesday.

The most common terrestrial form of phosphorus is a mineral called apatite. When mixed with water, apatite releases only very small amounts of phosphate, the oxidized form in which phosphorus naturally is found. Scientists have tried heating apatite to high temperatures, combining it with various strange, super-energetic compounds.

"These experiments tended to use chemicals that were probably uncommon on the early Earth, so it's unclear how applicable they are to geochemical systems," Pasek told Astronomy. "It's more intuitive to use simpler and more common compounds, such as those found in meteorites."

Lauretta conducted experiments showing that metal surfaces corroded in the early solar system in a way that concentrated phosphorus on them. "This natural mechanism of phosphorus concentration in the presence of … iron-based metal … made me think that … corrosion of meteoritic minerals could lead to the formation of important phosphorus-bearing biomolecules," he explained.

Inspired by these experiments, Pasek and Lauretta began looking at meteorites as a possible source of the element. Meteorites contain several different phosphorus-bearing minerals, but the most important, said Pasek, is iron-nickel phosphide, also known as schreibersite. This metallic compound is extremely rare on Earth, but iron meteorites are peppered with schreibersite grains or even pinkish-colored veins of the mineral. Iron meteorites became the focus of the study because schreibersite is between 10 and 100 times more common in iron meteorites than other types.

Last April, Pasek, Lauretta, and undergraduate student Virginia Smith, mixed schriebersite with de-ionized water at room temperature. They then analyzed the liquid mixture using nuclear magnetic resonance. "We saw a whole slew of different phosphorus compounds being formed," Pasek said. "One of the most interesting ones we found was P₂O₇, one of the more biochemically useful forms of phosphate, similar to what's found in ATP." The analysis revealed numerous phosphate salts in different states of oxidation, Pasek told Astronomy.

Previous experiments have formed P₂O₇, or pyrophosphate, but at high temperature or under other extreme conditions. "This allows us to somewhat constrain where the origins of life may have occurred," Pasek said. "If you are going to have phosphate-based life, it likely would have had to occur near a freshwater region where a meteorite had recently fallen. We can go so far, maybe, as to say it was an iron meteorite."

Meteorites were critical for the evolution of life, argues Pasek, because of minerals like pyrophosphate, which is used in ATP, in photosynthesis, in forming new phosphate bonds with carbon-bearing compounds, and in a variety of other biochemical processes.

"I think one of the most exciting aspects of this discovery is the fact that iron meteorites form by the process of planetesimal differentiation," Lauretta noted. The building blocks of planets, called planestesimals, form both a metallic core and a silicate mantle. Iron meteorites come from the metallic core, and other types of meteorites, called achondrites, represent the rocky mantle. Today's asteroids are what remains of our solar system's population of planetesimals.

Life's limiting element links the origin of life to a specific time and place in the solar system's history. "No one ever realized that such a critical stage in planetary evolution could be coupled to the origin of life," Lauretta said. This connection also suggests the environment needed for life elsewhere. The first ingredient is an asteroid belt, where planetesimals can grow to about 300 miles (500 kilometers) across, large enough to form metal cores and stony mantles.

The second requirement, say Pasek and Lauretta, is a mechanism to break up these bodies and deliver them to the inner solar system. Today, Jupiter's gravity perturbs asteroids from stable orbits, herding them toward the inner solar system — and Earth — and also causing them to collide with one another, creating meteorites.

If this scenario is correct, Lauretta argues, then the reactive forms of phosphorus needed by biological molecules — and so essential to terrestrial life — were denied to planets and moons of the outer solar system, limiting the prospects for life there. Likewise, he said, life is less probable in solar systems without a Jupiter-size world able to perturb mineral-rich asteroids toward rocky planets closer to their suns.

(ed note: this is taking place in a Lunar city)

All human communities, wherever they may be in space, follow the same pattern. People were getting born, being cremated (with careful conservation of phosphorus and nitrates), rushing in and out of marriage, moving out of town, suing their neighbors, having parties, holding protest meetings, getting involved in astonishing accidents, writing Letters to the Editor, changing jobs—Yes, it was just like Earth. That was a somewhat depressing thought. Why had Man ever bothered to leave his own world if all his travels and experiences had made so little difference to his fundamental nature? He might just as well have stayed at home, instead of exporting himself and his foibles, at great expense, to another world.

(ed note: Some space colonies might get a little strict about tourists who eat more phosphorus than they excrete. )

After a while the style settles down a bit and it begins to tell you things you really need to know, like the fact that the fabulously beautiful planet Bethselamin is now so worried about the cumulative erosion by ten billion visiting tourists a year that any net imbalance between the amount you eat and the amount you excrete whilst on the planet is surgically removed from your bodyweight when you leave: so every time you go to the lavatory it is vitally important to get a receipt.

(ed note: and such space colonies might take a dim view of people born in the colony who want to emigrate, taking their store of phosphorus with them.)

• 

     Space travel may be more common in the 22nd Century, but while it is cheaper and more efficient, that doesn't make it easy to move. While Mars has its temptations for certain types of Terran malcontents, to settle there takes quite the commitment—and quite a bit of chnops.
     Originally, it was literally CHNOPS—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, the six most common elements in life. Mars had much of those, already, but on a lifeless planet you need as much CHNOPS, preferably as aqueous solutions, as you can get.
     The original standard set by the Planetary Trust was based on a candidate's mass at age 21, or if not known, the average mass based on body type. You were expected, in essence, to bring five times your mass in CHNOPS. There were asteroid mining firms who would be happy to assist you for a fee. If not, they could hire you to mine the stuff for five years, and pay your CHNOPS to Mars for you.
     Unless, of course, you had those sorts of unfortunate personal issues that might leave you unable to meet your quota or pay off the expenses you incurred while under their employ. They can extend the contract another five, or twenty, years if need be.
     (The average Martian, incidentally, is horrified by the exploitive nature of the system, but also struggles to figure out what to do about it. The most common proposal, to allow provisional resident status and have them help mine Mars, isn't guaranteed to be an improvement.)
     Eventually chnops became a matter of accounting, and thus a semi-official Martian currency. The Planetary Trust became a treasury, for both cash and biomass—the latter including a thorough census of every Martian, immigrant or native, and an accounting for their remains after death.
     Your covenant to the Trust isn't just for the CHNOPS you brought outside your body, after all—you're committing for your remains to be used to grow some sort of plant. Dr. Jeferson Schefer, for example, was buried under a sapling of Elysium hazel, a tradition his family has followed since. You can buy hazelnuts from them, of course.
     In the mid-22nd Century, the Trust began to shift the requirements away from pure CHNOPS, in favor of other minerals—more platinum-family elements, for instance. That is generally attributed to tensions over rights to Deimos.
     Since the beginning of Martian exploration and colonization, Deimos was critical as a fuel depot and mining base. Its spaceport's legend, "DEIMOS FOR ALL," reminded everyone that it was a port co-managed by Earth and Mars. Even leading up to the War, Deimos was a place where humans of all worlds could mingle, do business, and consider options.
     This was usually the last stop before Mars-side, the point of no return for many an augment looking for a new beginning. If they can't handle the Martians on Deimos, they better hope for a quick refund in chnops—even if they paid in real CHNOPS—and that the Moon could put them to use.
     Also, Deimos is where you were screened to see if you were in fact augmented. If not, you were usually given the choice of accepting the augmentation as a matter of public health, or accepting a refund from the Trust.
     Hostels are a growth industry on Deimos--there are about 200 people at any time, either waiting for their augmentation therapy date, or waiting for a refund. Technically, there are more Terrans on Deimos than Martians, which is why co-management is required. The Terrans provide the public security and handles the transfer of citizenship and identification from Earth to Mars. Mars focuses on processing the new residents, arranging for basic income and identifying prospective communities based on personality and skills.
     And if you can manage the journey, the expense, the probable toil, and the inevitable bureaucracy, you can at last plant your feet on red soil and begin to make your new home.

• 

     Over the weekend I got asked a question: How does Mars contribute to the interplanetary economy, given its economic foundation in CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur) seems to preclude exports in the normal sense?
     First, bear in mind that it's not just that, per the Martian Charter, CHNOPS is to be conserved and cannot be exported from Mars.
     As mentioned previously, the tyranny of the rocket equation still holds a firm grip in the 22nd Century. With Mars' shallower gravity well, it's slightly easier to launch ships into space — and its currently thin atmosphere makes it much easier as well. But the logarithmic relationship between dry mass and wet mass still means that you need exponentially larger ships to launch larger payloads.
     Plus, even in the 22nd Century, your choice of propellants are still, technically, CHNOPS. Whether you use cryogenic hydrogen/oxygen fuel, dinitrogen tetroxide with hydrazine, or methane with cryogenic oxygen, you're using elements that Mars would generally prefer be reserved for biomass.
     So how does Mars get to space?
     Through loopholes, of course.
     Mars won't let you use their CHNOPS to create rocket fuel. But, Deimos is outside of the Martian Charter's jurisdiction. So typically ships will be built and fueled on Deimos, sent down to the Martian surface to be loaded, and then launched back to Deimos.
     The side benefit, from the long term view, is that all that Deimos fuel spent on Mars, winds up becoming part of Mars' total CHNOPS count, even if it isn't currently bound up in biomass. It's not like all that spent propellant is going anywhere quickly.*

* Long term, until the magnetosphere question is resolved, pretty much all gases in Mars' atmosphere will wind up being blasted off the planet by the solar wind. Short term, it's adding, albeit slowly, to the oxygen and water vapor in the atmosphere. Mars considers it a win.

     But that's all dancing around the question.
     The real answer is, Mars tends to provide intangibles — services like their asteroid detection network, or their expertise in coding and training fourth-generation deepers. There is a limited export in things Mars has in abundance, mostly iron. But even then, most of it winds up at Deimos, for spaceship construction. Mars isn't all that fond of plastics, either — that's a luxury of a world that originally thought fossil fuels would last forever. Where plastic must be used, it's kept in forms that can be recycled, even if by means of supercritical water oxidization.
     Until the sol comes when torchships are practical and Mars no longer needs to account for every mole of CHNOPS in the biosphere, Mars won't be creating consumer goods for non-Martian consumption. Mars considers the ecological disaster that Earth has become, a stern warning about what happens when you presume economic growth can be infinite. They aren't eager to repeat the mistake.

(ed note: And if a space colony is really hard up for phosphorus, they might institute an age limit. No child can be born until somebody dies. The longer you live, the longer before the colony can afford a new birth. The elderly will have to prove that they are worth the phosphorus they are tying up. Or face euthanasia when your reach the mandated maximum age.)

     'Look! Look there!' Grew's voice was a whispered rasp. 'You see the horizon? You see it shine?'
     'Yes.'
     'That is Earth — all Earth. Except here and there, where a few patches like this one exist.'
     'I don't understand.'
     'Earth's crust is radioactive. The soil glows, always glowed, will glow forever. Nothing can grow. No one can live — You really didn't know that? Why do you suppose we have the Sixty?'
     The paralytic subsided. He circled his chair about the table again. 'It's your move.' (ed note: they are playing chess)

---

     Schwartz said finally, 'What — what is the Sixty?'
     There was a sharp unfriendliness to Grew's voice. 'Why do you ask that? What are you after?'
     'Please,' humbly. He had little spirit left in him. 'I am a man with no harm in me. I don't know who I am or what happened to me. Maybe I'm an amnesia case.'
     'Very likely,' was the contemptuous reply. 'Are you escaping from the Sixty? Answer truthfully.'
     'But I tell you I don't know what the Sixty is!'
     Grew said slowly, 'The Sixty is your sixtieth year. Earth supports twenty million people, no more. To live, you must produce. If you cannot produce, you cannot live. Past Sixty — you cannot produce.'
     'And so …' Schwartz's mouth remained open.
     'You're put away. It doesn't hurt.'
     'You're killed?'
     'It's not murder,' stiffly. 'It must be that way. Other worlds won't take us, and we must make room for the children some way. The older generation must make room for the younger.'
     'Suppose you don't tell them you're sixty?'
     'Why shouldn't you? Life after sixty is no joke … And there's a Census every ten years to catch anyone who is foolish enough to try to live. Besides, they have your age on record.'
     'Not mine.' The words slipped out. Schwartz couldn't stop them. 'Besides, I'm only fifty — next birthday.'
     'It doesn't matter. They can check by your bone structure. Don't you know that? There's no way of masking it. They'll get me next time … Say, it's your move.'
     Schwartz disregarded the urging. 'You mean they'll —'
     'Sure, I'm only fifty-five, but look at my legs. I can't work, can I? There are three of us registered in our family, and our quota is adjusted on a basis of three workers. When I had the stroke I should have been reported, and then the quota would have been reduced. But I would have gotten a premature Sixty, and Arbin and Loa wouldn't do it. They're fools, because it has meant hard work for them — till you came along. And they'll get me next year, anyway … Your move.'
     'Is next year the Census?'
     That's right … Your move.'
     'Wait!' urgently. 'Is everyone put away after sixty? No exceptions at all?'
     'Not for you and me. The High Minister lives a full life, and members of the Society of Ancients; certain scientists or those performing some great service. Not many qualify. Maybe a dozen a year … It's your move!'