"Pegasus to Acheron. How do you suggest we can assist you?" It was eerie to be speaking to a man who was already as good as dead. The traditions of space were as strict as those of the sea. Five men could leave the Acheron alive, but her captain would not be among them.

Halstead did not know that Commodore Brennan had other ideas, and had by no means abandoned hope, desperate though the situation on board the Acheron seemed. His chief medical officer, who had proposed the plan, was already explaining it to the crew.

"This is what we're going to do," said the small, dark man who a few months ago had been one of the best surgeons on Venus. "We can't get at the airlocks, because there's vacuum all round us and we've only got five suits. This ship was built for fighting, not for carrying passengers, and I'm afraid her designers had other matters to think about besides Standard Spaceworthiness Regs. Here we are, and we have to make the best of it.

(ed note: details here)

• 

(ed note: Arcot and Morey have invented a handwavium reactionless thruster. They use it to make a prototype revolutionary aircraft. But before they can use it the craft will have to be certified.)

      “Dick,” said Morey as he strode up to him after testing the last of the gyroscopic seats, “she's ready! I certainly want to get her going—it's only three-thirty, and we can go around to the sunlight part of the world when it gets dark at the speeds we can travel. Let's test her now!”
     “I'm just as anxious to start as you are, Bob. I've sent for a U.S. Air Inspector. As soon as he comes we can start. I'll have to put an 'X' license indication on her now. He'll go with us to test it—I hope. There will be room for three other people aboard, and I think you and Dad and I will be the logical passengers.”
     He pointed excitedly. “Look, there's a government helicopter coming. Tell the men to get the blocks from under her and tow her out. Two power trucks should do it. Get her at least ten feet beyond the end of the hangar. We'll start straight up, and climb to at least a five mile height, where we can make mistakes safely. While you're tending to that, I'll see if I can induce the Air Inspector to take a trip with us.”
     Half an hour later the machine had been rolled entirely out of the shed, on the new concrete runway.
     The great craft was a thing of beauty shimmering in the bright sunlight The four men who were to ride in it on its maiden voyage stood off to one side gazing at the great gleaming metal hull. The long sweeping lines of the sides told a story of perfect streamlining, and implied high speed, even at rest. The bright, slightly iridescent steel hull shone in silvery contrast to the gleaming copper of the power units' heat-absorption fins. The great clear windows in the nose and the low, streamlined air intake for the generator seemed only to accentuate the graceful lines of the machine.
     “Lord, she's a beauty, isn't she, Dick!” exclaimed Morey, a broad smile of pleasure on his face.
     “Well, she did shape up nicely on paper, too, didn't she. Oh, Fuller, congratulations on your masterpiece. It's even better looking than we thought, now the copper has added color to it. Doesn't she look fast? I wish we didn't need physicists so badly on this trip, so you could go on the first ride with us.”
     “Oh, that's all right, Dick, I know the number of instruments in there, and I realize they will mean a lot of work this trip. I wish you all luck. The honor of having designed the first ship like that, the first heavier-than-air ship that ever flew without wings, jets, or props—that is something to remember. And I think it's one of the most beautiful that ever flew, too.”
     “Well, Dick,” said his father quietly, “let's get under way. It should fly—but we don't really know that it will!”
     The four men entered the ship and strapped themselves in the gyroscopic seats. One by one they reported ready.
     “Captain Mason,” Arcot explained to the Air Inspector, “these seats may seem to be a bit more active than one generally expects a seat to be, but in this experimental machine, I have provided all the safety devices I could think of. The ship itself won't fall, of that I am sure, but the power is so great it might well prove fatal to us if we are not in a position to resist the forces. You know all too well the effect of sharp turns at high speed and the results of the centrifugal force. This machine can develop such tremendous power that I have to make provision for it.
     “You notice that my controls and the instruments are mounted on the arm of the chair really; that permits me to maintain complete control of the ship at all times, and still permits my chair to remain perpendicular to the forces. The gyroscopes in the base here cause the entire chair to remain stable if the ship rolls, but the chair can continue to revolve about this bearing here so that we will not be forced out of our seats. I'm confident that you'll find the machine safe enough for a license. Shall we start?”
     “All right, Dr. Arcot,” replied the Air Inspector. “If you and your father are willing to try it, I am.”
     “Ready, Engineer?” asked Arcot.
     “Ready, Pilot!” replied Morey.
     “All right—just keep your eye on the meters, Dad, as I turn on the system. If the instruments back there don't take care of everything, and you see one flash over the red mark—yank open the main circuit. I'll call out what to watch as I turn them on.”
     “Ready son.”
     “Main gyroscopes!” There was a low snap, a clicking of relays in the rear compartment, and then a low hum that quickly ran up the scale. “Main generators!” Again the clicking switch, and the relays thudding into action, again the rising hum. “Seat-gyroscopes.” The low click was succeeded by a quick shrilling sound that rose in moments above the range of hearing as the separate seat-gyroscopes took up their work. “Main power tube bank!” The low hum of the generator changed to a momentary roar as the relays threw on full load. In a moment the automatic controls had brought it up to speed.
     “Everything is working perfectly so far. Are we ready to start now, son?”
     “Main vertical power units!” The great ship trembled throughout its length as the lift of the power units started. A special instrument had been set up on the floor beside Arcot, that he might be able to judge the lift of his power units; it registered the apparent weight of the ship. It had read two hundred tons. Now all eyes were fixed on it, as the pointer dropped quickly to 150-100-75-50-40-20-10—there was a click and the instrument flopped back to 300—it was registering in pounds now! Then the needle moved to zero, and the mighty structure floated into the air, slowly moving down the field as a breeze carried it along the ground
.     The men outside saw it rise swiftly into the sky, straight toward the blue vault of heaven. In two or three minutes it was disappearing. The glistening ship shrank to a tiny point of light; then it was gone! It must have been rising at fully three hundred miles an hour!
     To the men in the car there had been a tremendous increase in weight that had forced them into the air cushions like leaden masses. Then the ground fell away with a speed that made them look in amazement. The house, the construction shed, the lake, all seemed contracting beneath them. So quickly were they rising that they had not time to adjust their mental attitude. To them all the world seemed shrinking about them.
     Now they were at a tremendous height; over twenty miles they had risen into the atmosphere; the air about them was so thin that the sky seemed black, the stars blazed out in cold, unwinking glory, while the great fires of the sun seemed reaching out into space like mighty arms seeking to draw back to the parent body the masses of the wheeling planets. About it, in far flung streamers of cold fire shone the mighty zodiacal light, an Aurora on a titanic scale. For a moment they hung there, while they made readings of the meters.
     Arcot was the first to speak and there was awe in his voice. “I never began to let out the power of this thing! What a ship! When these are made commercially, we'll have to use about one horsepower generators in them, or people will kill themselves trying to see how fast they can go.”
     Methodically the machine was tried out at this height, testing various settings of the instruments. It was definitely proven that the values that Arcot and Morey had assigned from purely theoretical calculations were correct to within one-tenth of one percent. The power absorbed by the machine they knew and had calculated, but the terrific power of the driving units was far beyond their expectations.
     “Well, now we're off for some horizontal maneuvers,” Arcot announced. “I'm sure we agree the machine can climb and can hold itself in the air. The air pressure controls seem to be working perfectly. Now we'll test her speed.”
     Suddenly the seats swung beneath them; then as the ship shot forward with ever greater speed, ever greater acceleration, it seemed that it turned and headed upward, although they knew that the main stabilizing gyroscopes were holding it level. In a moment the ship was headed out over the Atlantic at a speed no rifle bullet had ever known. The radio speedometer needle pushed farther and farther over as the speed increased to unheard of values. Before they left the North American shoreline they were traveling faster than a mile a second. They were in the middle of the Atlantic before Arcot gradually shut off the acceleration, letting the seats drop back into position.
     A hubbub of excited comments rose from the four men. Momentarily, with the full realization of the historical importance of this flight, no one paid any attention to anyone else. Finally a question of the Air Inspector reached Arcot's ears.
     “What speed did we attain, Dr. Arcot? Look—there's the coast of Europe! How fast are we going now?”
     “We were traveling at the rate of three miles a second at the peak.” Arcot answered. “Now it has fallen to two and a half.”
     Again Arcot turned his attention to his controls. “I'm going to try to see what the ultimate ceiling of this machine is. It must have a ceiling, since it depends on the operation of the generator to operate the power-units. This, in turn, depends on the heat of the air, helped somewhat by the sun's rays. Up we go!”
     The ship was put into a vertical climb, and steadily the great machine rose. Soon, however, the generator began to slow down. The readings of the instruments were dropping rapidly. The temperature of the exceedingly tenuous air outside was so close to absolute zero that it provided very little energy.
     “Get up some forward speed,” Morey suggested, “so that you'll have the aid of the air scoop to force the air in faster.”
     “Right, Morey.” Arcot slowly applied the power to the forward propulsion units. As they took hold, the ship began to move forward. The increase in power was apparent at once. The machine started rising again. But at last, at a height of fifty-one miles, her ceiling had been reached.
     The cold of the cabin became unbearable, for every kilowatt of power that the generator could get from the air outside was needed to run the power units. The air, too, became foul and heavy, for the pumps could not replace it with a fresh supply from the near-vacuum outside. Oxygen tanks had not been carried on this trip. As the power of the generator was being used to warm the cabin once more, they began to fall. Though the machine was held stable by the gyroscopes, she was dropping freely; but they had fifty miles to fall, and as the resistance of the denser air mounted, they could begin to feel the sense of weight return.
     “You've passed, but for the maneuvers, Dr. Arcot!” The Air Inspector was decidedly impressed. “The required altitude was passed so long ago—why we are still some miles above it, I guess! How fast are we falling?”
     “I can't tell unless I point the nose of the ship down, for the apparatus works only in the direction in which the ship is pointed. Hold on, everyone, I am going to start using some power to stop us.”
     It was night when they returned to the little field in Vermont. They had established a new record in every form of aeronautical achievement except endurance! The altitude record, the speed record, the speed of climb, the acceleration record—all that Arcot could think of had been passed. Now the ship was coming to dock for the night. In the morning it would be out again. But now Arcot was sufficiently expert with the controls to maneuver the ship safely on the ground. They finally solved the wind difficulty by decreasing the weight of the ship to about fifty pounds, thus enabling the three men to carry it into the hangar!

• 

America’s national spacefaring enterprise is changing at a pace that has not been seen since the 1960s when space was first accessed on a routine basis. The president’s plans for a US Space Force, others calling for a US Space Guard, a renewed focus on reusability in space launch and on American human space exploration and commercial human spaceflight, and Congressional interest in space-based ballistic missile and satellite defense, are all putting America’s spacefaring future in the public spotlight.

America will not effectively become a true human spacefaring nation without the ability to achieve “aircraft-like access to space.” In this article, I focus on what “aircraft-like access to space” means and why achieving airworthiness certification for commercial passenger spaceflight is necessary to enable aircraft-like access to space to be safely and ethically achieved. (A US Space Force and a US Space Guard will need a comparable capability for any crewed operations they might conduct in space.)

Understanding what “aircraft-like access to space” means

As you read this on a typical morning or afternoon, thousands of commercial airliners, carrying around a half-million people, cruise America’s skies in comfort and safety, as illustrated above. Air travel’s convenience makes it the preferred means for most business and leisure travel. This past July 4th holiday, more than three million Americans traveled by air. We are now 60 years into the jet age of commercial air travel and this industry’s safety and convenience define what “aircraft-like” means to the public.

In the mid-1960s, during the first decade of the human space age, director Stanley Kubrick set out to forecast what our spacefaring civilization would be doing 30 years in the future, in 2001. America’s human spaceflight program was then just beginning two-person missions with the Gemini program. Author Adam K. Johnson superbly records, in 2001: The Lost Science, the technical and industrial expertise Kubrick harnessed in preparing the movie. Kubrick’s depiction of the two-stage-to-orbit Orion III passenger shuttle established our expectations of what “aircraft-like access to space” should be like. While some see the traditional aircraft-like appearance of the Orion III to be what “aircraft-like access to space” means, aerospace engineers understand that the key attribute—as depicted by Dr. Heywood Floyd sleeping in the passenger compartment of the Orion shuttle—was flight safety or airworthiness.

For leisure air travel, Americans routinely take their children while older children often travel by air unaccompanied. Especially with the safety of our children being paramount, the public has high expectations for the safety of air travel. If we are to normalize human space travel, then it must also be made acceptably safe so that working adults—many who have families—will be able to travel to, from, and within space with safety comparable to air travel.

For aircraft, acceptable safety is achieved through airworthiness certification. Comparable airworthiness certification will be needed for human spaceflight systems to achieve “aircraft-like access to space.” Whether the actual space flight system has wings, takes off from a runway, or launches vertically from a pad is not relevant to achieving “aircraft-like” access to space. How it is accomplished is up to the engineers, provided acceptable safety can be adequately demonstrated to an independent federal agency legally charged with protecting the safety of the involved and non-involved public.

Why airworthiness is a legal and ethical necessity

To understand the legal need for airworthiness, we need to start with the roots of how a legal obligation for commercial safety came about. The legal obligation for business owners and operators to be responsible for the safety of their customers arose, per my understanding, nearly 4,000 years ago in the ancient Code of Hammurabi.

If a builder build a house for someone, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death.

This criminal legal code—essentially an “eye for an eye” act of vengeance for a harm having been caused—was the basis of Western civilization’s law for several millennia. Two thousand years later, in ancient Rome, accountability expanded to hold a business owner at fault even if the act causing harm was done by an employee or slave. Roman law held that the shipowner and innkeeper “was to a certain degree guilty of negligence in having employed the services of bad men.” The owner incurred guilt even though someone else may have been directly to blame.

This Roman law obligation continued until the emergence of British common law in the 1400s. Not being a lawyer, my understanding is that British common law is based on the concept of legal precedence where court decisions (and British customs) establish the law going forward.

In the late 1500s and early 1600s, British common law established that those engaged in business with the public carried a legal obligation “to exercise his art rightly and truly as he ought.” Over time, this obligation became known as a “duty to care”. Those engaged in the transportation of people—legally referred to as passengers—clearly carried this obligation as it was not realistic that a passenger could know if a vehicle was roadworthy or a ship was seaworthy and adequately provisioned for the voyage. (It is my understanding that the commercial use of the term “passenger” implies acknowledgement of the “duty to care” obligation. Some companies now talk about taking fare-paying individuals to space rather than using the term “passenger.” This comes across to me as an intentional avoidance of acknowledging a duty-to-care obligation. Also, I believe some writers incorrectly use the term “passenger” when discussing what federal law now refers to as “spaceflight participants”. Such likely incorrect use only confuses the public.)

In the United States, each individual state defines the law governing the duty-to-care obligation for commerce within the state. However, for interstate commerce, the federal government regulates the duty to care obligation through its constitutional power “to regulate Commerce with foreign Nations, and among the several States, and with Indian Tribes.”

In the 1800s, as industrialization took hold, technology advanced rapidly. Construction with metals replaced stone and timber. Steam engines powered land and water transportation. Electricity was commercialized. By the late 1800s, injuries due to faulty construction and equipment failure increased significantly. Improperly prepared foods and drugs caused illness and death. Congress took steps to impose safety regulations to protect the public and workers from harm and to alleviate some lawsuits by having the federal government assume some responsibility for assuring safety. This was achieved by imposing design and operating requirements and undertaking independent safety inspections. Railroads were addressed first followed by food and drug regulation.

The emergence of the profession of engineering

The world’s transition to industrialization in the 1800s was enabled by the steam engine; the genius invention of Thomas Newcomen in 1712 which enabled a simple fire to produce useful mechanical power. Industrialization requires the ability to use metals in safety-critical applications—such as steam boilers—where failure can lead to injury and death. In addition to civil engineering—focused on roads, bridges, canals, and ports—mechanical engineering emerged to handle industrialization.

As the United States saw the need to regulate industrialization to achieve acceptable safety, the professional role of engineering changed accordingly. Engineers increasingly relied less on “rules of thumb” and more on scientifically-established principles and practices to design safety-critical machines and installations. Notable failures of boilers, bridges, and dams, as examples, hastened the awareness of the need for these changes. In 1907, Wyoming began the examination and registration of anyone engaged in engineering to clarify that a duty-to-care obligation existed for engineering works that impacted public safety and that only registered professional engineers could legally carry out such work. (A similar process now exists in many fields, such as architecture and medicine.) From this start arose the engineering ethical obligation, adopted by professional engineering societies, to protect the public from avoidable harm by using the best available principles and practices.

The emergence of airworthiness

In the 1920s, Congress passed laws creating the need for the emerging airline and aircraft manufacturing industry to achieve federal airworthiness certification. The fledgling airlines were suffering an unacceptable number of accidents. With airlines clearly interstate commerce, and with Congress taking steps and investing federal funds to promote air travel, the imposition of airworthiness certification to boost the public’s confidence in the fledgling industry’s safety was a logical step. The positive results speak for themselves. Air safety improved, making air travel increasingly common. Part of this process was the adoption of specifications and standards for the manufacture of materials and some parts used to build aircraft (e.g., fasteners), and for the methods used to design, build, test, and inspect aircraft. Many of these specifications and standards became military procurement specs and standards during World War II and the ensuing Cold War.

In the United States, airworthiness certification negates the need for engineers engaged in the human flight industry to be registered professional engineers (PE) or work for a PE. In other commercial engineering disciplines, the PE’s act of signing or stamping an engineering document or drawing acknowledges the PE’s legal responsibility for the work. (In a field where such a requirement exists, only a PE is properly referred to as an engineer.) If something goes wrong through error, the PE is held responsible. While there may still be independent inspections, such as building inspections, the PE remains legally responsible.

The federal civil, commercial, and military airworthiness certification processes essentially remove the requirement that a PE oversee and be responsible for the work. (However, within the aerospace industry, many engineers are PEs—doing this, often, to show personal adherence to professional ethical obligations.) The primary reason for this difference is that the airworthiness certification process includes substantial ground and flight testing, often including the ground testing of articles to failure to verify the conservatism of the predicted performance. Such destructive testing cannot be replicated for typical terrestrial constructions such as bridges, buildings, and dams. Government engineers and pilots, especially for military systems, have access to and often directly observe the airworthiness testing and undertake government flight testing.

In having the final say about the aircraft’s airworthiness, the federal government assumes the duty-to-care responsibility when it issues an airworthiness certificate. For civil and commercial aircraft, the Federal Aviation Administration (FAA) directs the procedures and processes to be followed to achieve and maintain airworthiness and correct deficiencies that are later identified. The military has comparable airworthiness procedures and processes but extends its oversight role to include performance and mission capability.

Benefits of government safety certification

Today, most businesses operate quite successfully within a framework of government safety oversight that limits the public or employee’s possible harm when they engage in commerce. Per my understanding, with the government inspectors’ independent approval, the business operator’s duty-to-care obligation is met. This shields the business operator from legal claims of harm except where negligence can be proven. Also, when an approved product or operation is used, no informed consent is required, absent some further consideration due to age or health. Obviously, this legal protection benefits commerce significantly. Of course, mistakes can happen and unexpected failures can occur that cause harm. When this happens, safety criteria and requirements are modified to try to prevent a reoccurrence. Impacted systems are withdrawn from service until appropriate inspections and changes are made and recertification is achieved. (The FAA issues Airworthiness Directives to mandate needed changes.) The intent of government safety oversight is not to prevent all harm, but to keep the occurrence at an acceptable very low rate such that normal commerce can proceed without undo concern or serious disruptions should failures occur.

An often-overlooked aspect of this safety regime is that it also helps to shield professionals working in private industry from legal risk. The business owners and operators understand that the safety of their product or service will be thoroughly reviewed by independent experts before commercial use can begin to verify that approved safety protocols have been implemented. Identified deficiencies will be corrected, often at a substantial additional expense. Intentional acts resulting in unsafe products or services may have both civil and criminal consequences. Practicing professionals benefit because independent safety certification helps to prevent unsafe products and services from entering commercial use and causing harm.

Airworthiness does not preclude technology advancement

As everyone is aware, there is a surge in interest and private investment in electric-powered, VTOL air taxis that will carry fare-paying passengers. Rather than trying to avoid airworthiness certification—perhaps by claiming that mandating airworthiness precludes rapid technology advancement—electric VTOL air taxi developers are working closely with the FAA to make sure that airworthiness is achieved.

One such prototype two-person air taxi has received an experimental airworthiness certificate permitting test flights with two people on board to simulate passengers being transported by the taxi. The pilot would remain on the ground as the vehicle only carries two people. The test participants cannot be fare-paying passengers. With final airworthiness certification, the air taxi would operate carrying fare-paying passengers even if this was just for a local “joyride” to see the sights from the air. There is no reason why this model of handling technology advancement should not be applied to commercial human spaceflight.

Informed consent use in commerce

Going back to the 1500s, common law established a duty-to-care obligation by those engaged in commerce to protect the public. Under some circumstances, such as war or piracy, this obligation is waived. In modern times, it has also been waived in some areas of intrastate commerce.

Informed consent in voluntary commerce—as opposed to medical treatment—ethically requires that a reasonable person understands the risks. One common example where state laws permit the use of informed consent is river rafting. While rafting is a form of transportation, whitewater river rafting is deemed to be entertainment and not subject to the duty-to-care obligation required for fare-paying passenger transport. The distinction appears to be that such rafting does not exist to transport a person to a destination.

Not being a lawyer, it is my understanding that the legal presumption is that the simplicity of rafting enables responsible adults to make an informed decision regarding the inherent risks of injury or drowning. Does the raft appear sound? Is the guide competent and not intoxicated? Are the water conditions abnormally dangerous, such as following heavy rains? Is the safety equipment, such as helmets and life jackets, in good condition? If customers conclude that they should be safe, they sign an informed consent waiver absolving the rafting company of liability in most circumstances. The state may impose some basic regulations, such as wearing life vests and helmets, setting a minimum age or physical condition, or not being intoxicated, but the rest is left up to the adult or, in the case of older children, the parent or guardian to decide. Hence, rafting, mountain climbing, and similar commercial activities are permitted because it is presumed that an informed decision regarding one’s safety can be made. Further, the adult can physically inspect the equipment and question the operators to enhance their understanding and evaluation of the risk.

State court decisions determine any exceptions to the use of informed consent. When harm occurred on one rafting trip, an attempt to sue under the duty to care obligation was turned back by the court because, per my understanding, an informed consent waiver had been signed and this was deemed adequate for this form of entertainment commerce. However, in another case, when harm occurred on a theme park ride, the state court decided that the duty to care obligation held, overturning the expectation that purchasing a ticket to the theme park constituted giving informed consent.

Imagine trying to apply an informed consent approach to the electric VTOL air taxis if used for pure sightseeing—a form of entertainment travel comparable to river rafting. Would a simple visual inspection of the aircraft provide sufficient information for a typical adult to ascertain its airworthiness? With no pilot, who would be asked pertinent questions? If being used as a taxi to a destination, would it be ethical for a company to demand its employees, as a condition of employment or advancement, use such an aircraft that lacked airworthiness certification, requiring instead that an informed consent be signed absolving the employer and the operator of legal liability?

Informed consent and commercial human spaceflight

No company, to the best of my knowledge, is currently seeking airworthiness certification of a commercial human spaceflight system. Thus, an informed consent approach appears to be the way commercial human spaceflight is now being pursued. The inherent presumption appears to be that a typical adult can, of their own accord, determine whether the risk is acceptable such as is now done for entertainment rafting. Obviously, human spaceflight systems will be far more complex than river rafts, theme park rides, or even, the new air taxis.

At what level of complexity does it become unreasonable to expect that a typical adult can, of their own accord, make a determination whether the risk is acceptable? Is it not the case that the inherent complexity of commercial human flight was why airworthiness certification was implemented: to take slick marketing and profit-seeking out of the safety decision process so that the air travel industry could mature and prosper? Imagine a commercial human spaceflight operator offering fare-paying service to transport people to Earth orbit. For commerce to develop in space, companies will require employees to travel to space. If it would not be ethical for the company to demand that employees consent to using air taxis that are not airworthiness certified, why would it be ethical to demand that they consent to travel to and from space on flight systems that are not airworthiness certified?

Today’s road to oblivion

With recognition that reliance on an informed consent approach to commercial human spaceflight is ethically wrong and, as courts may determine, contrary to the long-held common law duty-to-care obligation, it is clear that America’s human spacefaring enterprise is still dead in the water. Despite the billons being spent, America is not yet developing a true commercial passenger spaceflight industry.

As I have pointed out elsewhere, shortly after SpaceShipOne won the Ansari X PRIZE for private, suborbital human spaceflight, it was loudly touted that commercial human suborbital spaceflight was just a couple years away. Congress was told to stand aside and just let private industry takeover. More time has since elapsed without such a commercial capability coming into operation than it took this nation to land humans on the Moon after President Kennedy’s1961 speech. Further, the operators of the suborbital systems now being developed appear to plan to rely upon the informed consent approach to safety. What is being developed is fancy river rafting trips for the wealthy. While some people champion this as progress, clearly it is not.

The emerging electric VTOL air taxi industry is leading the way by embracing airworthiness as the means to provide a proper safety foundation for their industry. The federal government is working closely to make this a success. In sharp contrast, the US private commercial human spaceflight industry is on a road to oblivion. Strong federal government leadership is now required to correct this situation by focusing on airworthiness-certified “aircraft-like access to space” system development that will foster the creation of a commercial passenger spaceflight industry.

A US Space Force may require a military human presence in space to achieve the dominance that the President desires. For this reason, it is time for the military to lead in advancing America’s human spaceflight industrial mastery. As was done with the new US Air Force’s leadership in advancing jet aviation after World War II, such federal government leadership will enable military and commercial airworthiness-certified aircraft-like access to space to become as safe and routine as air travel is today.

• 

In 1968, a year prior to the Apollo 11 landing on the Moon, as a teenager I traveled to New York City for the first time. Growing up in a middle-class suburb in middle America, this was a remarkable experience—almost an alien encounter given the tremendous lifestyle differences between NYC and my quiet suburban city.

By coincidence, the now classic science fiction movie 2001: A Space Odyssey was opening that week. Billboards harking the opening were everywhere. Along with a group of other teenagers on this trip, I made a point of seeing the movie. Stanley Kubrick, with the help of many aerospace engineers, had created a detailed, technically accurate depiction of what humanity’s spacefaring near-future could be. The realism of Kubrick’s vision of this future was visually staggering, especially with the Super Panavision 70 Cinerama version projected on the large screen of a major NYC movie theater—an immersive experience missed on the home screen.

Dr. Heywood Floyd’s trip to space aboard the Orion III spaceliner—the orbiter part of a two-stage-to-orbit, fully-reusable commercial passenger spaceflight system—caught everyone by surprise. Compared to the three-person Apollo capsule atop the massive Saturn V, an ability to travel to space in comfort as a typical flight passenger, while wearing a business suit, set the standard for what the future of commercial passenger spaceflight “should be.” It is a goal that, 50 years later, we are still struggling to achieve, puzzled why this has not yet happened.

The focus of this three-part article is on commercial passenger spaceflight safety—what this ethically means and how to achieve it now. Without acceptable safety, a real version of Floyd’s travels to and within space will simply not happen. Despite what some would have us believe, outer space will not be permanently opened to commercial development and settlement without first establishing acceptably safe commercial passenger spaceflight.

The key question, of course, is what constitutes “acceptably safe” passenger spaceflight. Developing acceptably safe human systems is fundamental to the ethical practice of engineering. For some—the extraordinary risk takers—a real threat of death is part of the allure of the activity, such as climbing Mount Everest. In the civilized world—which many like myself hope to extend into space—risk is intentionally reduced through the implementation of the best-available engineering principles and practices. For air travel, these are embodied in airworthiness regulations. To truly open space to civilization, we must now carefully select the ethical path to achieve acceptable passenger spaceflight safety. Otherwise, more time and—especially—hard-to-replace funding will be wasted.

I am addressing this question in three parts. In this Part 1, I critique a proposal to establish a “regulated self-policing” approach to commercial human spaceflight safety certification. Finding the proposed approach, largely based on NASA’s “human-rated” safety process, to be unethical for commercial passenger use, I explain in Part 2 why the airworthiness approach yielding acceptably safe passenger air travel should be extended to all commercial passenger spaceflight. In the concluding Part 3, I describe how to proceed with creating an initial commercial passenger spaceflight industry, including a technical approach for developing a “DC-3” passenger spaceliner, as the initial step in building a broader American astrologistics infrastructure.

Making spaceflight safety a national priority

On the recent 50th anniversary of the Apollo 11 landing, one evening national news broadcast featured a 58-year-old woman. She was excited about the possibility that the long-awaited commercial suborbital spaceflight participant rides—legally not commercial spaceflight passenger rides—were “about” to commence.

Mesmerized by the billionaire boys of space, the “objective” news media has turned a blind eye to the safety of their version of human spaceflight. It is reminiscent of the lead-up to the fatal 1986 flight of the Space Shuttle Challenger, which was to fly the first civilian, a teacher, into space. The inherent risk the teacher was taking was part of the mission hype rather than a serious discussion of whether the teacher was intellectually capable of understanding and assessing the risk of losing her life—of making a true informed consent. Flying on the Space Shuttle was, we were then told, almost as safe as flying on an airliner. On that early shuttle mission, the probability of loss of crew is now estimated to have been 1 in 10; not the 1-in-1000 the public was led to believe. Yes, 1 in 10! Do you think that she—a schoolteacher and mother—would have signed on had she known this? Would the public have accepted this? Of course not!

NASA had turned the process of selecting the teacher into a giant publicity stunt. The selected teacher became a national media star. After disregarding known safety hazards with the seals in the giant solid rocket boosters, problems exacerbated on the exceptionally cold launch day in Florida, as the teacher boarded the shuttle, looking every bit an astronaut in her flight suit, her safety was not NASA’s foremost priority. The shocked world watched her and the rest of the crew die live on NASA TV. NASA’s public image of flight safety integrity evaporated.

We are repeatedly told that human spaceflight is inherently more dangerous. In its “human-rated” requirements document, NASA says “that a certain level of risk needs to be accepted to conduct human spaceflight.” This thinking will only open space to the foolishly bold and brave—such as those who free-climb mountains or wingsuit glide down mountainsides—or those who are wealthy but particularly naïve. I believe this mindset will lead to more Challenger-like failures in the future, such as the loss of the crew of the Columbia in 2003 due to poor safety decisions.

America must change course regarding human spaceflight safety. Achieving acceptable commercial passenger spaceflight safety must be made a national space policy priority if we are to open space to development and settlement. To understand why changes are needed, the two current federal approaches to human spaceflight safety must be explained.

The current federal law regarding suborbital human spaceflight is simply bizarre and immoral

Returning to the woman wishing to experience suborbital spaceflight, per federal law, assuring her safety is unimportant to the government. Should she undertake a commercial suborbital spaceflight, she will be required to sign a comprehensive waiver absolving everyone, especially including the government, of any liability should harm or death occur. Federal law presumes the average person has the wherewithal to ascertain the level of risk involved and the integrity of the spaceflight operations. This is nonsense!

To further confuse the topic of safety, federal law forbids the use of the standard commercial term “passenger,” instead substituting “spaceflight participant.” Only lawyers understand the legal significance of this change with respect to the owner/operator’s common law “duty to care” obligation regarding the safety of their passengers. The change to spaceflight participant generally abrogates this obligation.

One the same day as the 50th anniversary national news broadcast, the local news reported that several rides at the state fair were shut down due to not being assuredly safe. One was permanently shut down because of visible corrosion. Several years ago, a person died when a ride at that state fair failed. Now, per state law and common sense, the safety of the ride participants is paramount to the extent that the state government took on the final responsibility to inspect the rides to ascertain their safety and close rides where the safety could not be assured by operational inspection.

In our litigious world, public safety is increasing in importance—except in the area of human spaceflight. Per federal law, there is no current requirement for the federal government to inspect and ascertain the safety of a commercial suborbital human spaceflight system except to protect the safety of the public on the ground or flying in the shared airspace. Isn’t this bizarre! A state government will inspect a fair ride called “Travel to Space” to protect the public’s safety, but the federal government will not inspect and certify the acceptable safety of a commercial suborbital human spaceflight system to protect an American spaceflight participant engaged in this legal commerce. The current 2004 federal law addressing suborbital human spaceflight is immoral and must be changed.

NASA is currently responsible for orbital American spaceflight safety

For human orbital spaceflight originating in the United States, there is no current operational capability. NASA ended Space Shuttle operations in 2011 without, for the first time in US history, replacing an important national infrastructure with a better, safer capability. With NASA able to purchase rides to the International Space Station (ISS) from Russia, NASA did not have a true operational deficiency driving the development of an immediate replacement system. Instead, NASA focused on developing the Apollo-like Orion capsule spacecraft to be launched on the expendable Space Launch System and paying for the development of two smaller, less capable space capsules to transport astronauts to the ISS. This is the commercial crew program.

My understanding is that, per federal law, the NASA administrator is the authorizing authority for approving human spaceflight on NASA systems. To implement this authority, NASA developed its “human-rated” approach to human spaceflight safety. The “human-rated” approach has evolved over the years. NASA NPR 8705.2C, Human-Rating Requirements for Space Systems, is the current statement of NASA’s certification process and requirements. The following two quotations outline the purpose and responsibilities:

The purpose of this NASA Procedural Requirements (NPR) document is to define and implement the additional processes, procedures, and requirements necessary to produce human-rated space systems that protect the safety of the crew and passengers on NASA space missions.

The Program Manager is expected to evaluate the intent of these technical requirements and use the talents of the development and operation team to design the safest practical system that accomplishes the mission within constraints. By doing so, the program is expected to arrive at an optimal solution that represents the best overall value considering cost, schedule, performance, and safety. [emphasis added]

Note that safety is the “and” requirement, establishing its apparent importance in the hierarchy of program manager responsibilities; perhaps reflecting NASA’s acceptance of “a certain level of risk” and designing the “safest practical system that accomplishes the mission within constraints.” I think it is fair to say that these are inferior to the public’s expectations of the importance of safety for commercial systems providing public transportation services.

Space Shuttle probability of loss of crew

The Space Shuttle system was developed and operated under previous versions of NASA’s human-rated requirements. After the conclusion of shuttle operations, NASA was directed by its independent Aerospace Safety Advisory Panel to conduct a retrospective assessment of the probability of loss of crew (LOC) throughout the 30-year operational life of the system. The figure below shows the results For example, an LOC probability of 1 in 10 missions plots as a value of 0.1 or 10 percent. Notations indicate what changes were made to the shuttle system that affected the estimated LOC. The Challenger mission was #25 while the Columbia mission was #113.

The panel’s 2011 report noted, “In the Shuttle’s case, the first flight risk as now retrospectively calculated was in actuality 1 in 12 for LOC, yet at least one analysis that existed at the time of the initial launch estimated the risk to be 1 in 1,000 or better.” If the earlier analysis had predicted a 1 in 12 LOC probability on the first flight and this was known to the public, would the shuttle ever have flown? (Note that the retrospective LOC probability through Challenger mission #25 was 1 in 10.)

NASA made improvements to the Space Shuttle system throughout its operational life. Many of these, especially with the main engines, were noteworthy technological advances. However, even at the end of its 30-year history, the LOC probability had only improved to 1 in 90. By then, there had been two mission losses with the second mission—Columbia in 2003—being lost due to known but unresolved hazards related to the expendable External Tank’s external insulation.

It is reasonable to suspect that NASA had an idea of the actual low shuttle LOC probability throughout most of the 30 years. This helps us to understand what NASA really means when saying, in NPR 8705.2C, “that a certain level of risk needs to be accepted to conduct human spaceflight” and designing the “safest practical system that accomplishes the mission within constraints.”

It took the actions of NASA’s quasi-independent safety panel—after decades of operations—to publicly identify this substantial discrepancy between the implied safety of NASA’s “human-rated” safety regime and what was going on. This indicates that safety is apparently not the priority within NASA as the public has been led to believe as it is hard to believe that the true state of the Shuttle’s safety was unknown within NASA. Essentially, “human-rated” safety was whatever the NASA astronauts were willing to sign on to do.

It is best to think of NASA astronauts as being comparable to test pilots from the early days of aeronautics. Test pilots were the final judge of the airworthiness of a new aircraft based on the technical information gained from close observation of the aircraft’s development and the “feedback” from close program associates. Like test pilots, astronauts are employees voluntarily engaged in providing a service to their employer. Many employees volunteer for dangerous jobs—first responders, for example. Even then, however, normal life experience in the United States today does not provide an appreciation of what a 1-in-10 chance of death really means. Americans haven’t experienced this level of risk since World War II-era combat such as bombing missions over Germany.

The SpaceX Crew Dragon commercial crew system

As previously mentioned, NASA’s commercial crew program is developing several additional means of transporting NASA astronauts to the ISS. Two of these, as seen above, involve the use of capsules that will be launched on rockets. Both are nearing their first human flights. Somewhat of a surprise, NASA astronauts will be the first to fly rather than company astronauts—a reverse of the normal flight test approach for government-acquired aircraft.

A SpaceX Crew Dragon test capsule, Demo 1, was the first to fly—uncrewed—to the ISS. On its return to the Earth, it was recovered and processed for further testing. The company’s plan was to fly it a second time, also uncrewed, to activate and test the ascent escape system during an actual ascent.

The Crew Dragon capsule integrates the rockets needed for ascent escape into the base of the capsule. My understanding is that this design approach was selected by SpaceX to enable the capsule to be used for other missions where a powered landing, rather than parachutes, would be used. The ascent escape rocket engines are called SuperDraco.

Prior to launching this vehicle on its second flight test, the capsule’s SuperDraco engines were to be test fired in a ground static test. Less than a second before ignition of the SuperDracos during this ground test, a fire erupted destroying the capsule. As of this writing, investigation into the cause of the apparent failure is ongoing, although SpaceX says the most likely cause appears to involve valves that allowed fuel to leak through prior to pressurization of the system just before ignition. NASA has not yet released images of the capsule after that test, although some images and video are available online.

SpaceX’s test program to that point appears to have been competently undertaken. After the failure, NASA commented that, “Over the course of development, SpaceX has tested the SuperDraco thrusters hundreds of times.” In previous tests, the entire SuperDraco abort system had been test flown, but in a test capsule. My impression is that the ground static test was the first for a flight capsule during which a previously undiscovered design, manufacturing, or assembly error resulted in the fire. For this discussion of commercial passenger spaceflight safety, the reason why the Crew Dragon needed an ascent abort system is important to understand.

How “human-rated” safety drove the Crew Dragon design

At the end of its operational life, the Space Shuttle’s estimated LOC probability was still only 1 in 90. For the follow-on human spaceflight systems, my understanding is that NASA initially aimed to achieve a 1-in-1000 LOC probability—comparable to what the public was led to believe at the start of shuttle operations. This LOC estimate was not just for ascent but covered everything from the time the astronauts arrived at the launch pad to their return to land. Some of the hazards were human created, such as incorrect manufacturing or assembly, while some were natural, such as solar flares and space debris impact.

Early full-mission LOC probability estimates apparently found that achieving 1 in 1000 would be difficult, especially with unknown natural hazards acting on skimpy capsules. Consequently, per my understanding, NASA set the LOC target at three times the last shuttle value, which is 1 in 270. For the Commercial Crew Program, SpaceX and Boeing elected to propose developing—and NASA accepted—transport systems using conventional rockets and space capsules. It was up to these companies to provide an integrated system with their LOC probability no worse than 1 in 270. (Note that preparing probability estimates are actually quite complex. Saying the probability should be no worse than 1 in 270 is a simplification.)

Had the proposed systems been “aircraft-like” by being fully-reusable, each production system could have been flight tested to establish its proper functioning and actual operational safety prior to delivery to NASA for use in transporting astronauts to the ISS. Under such conditions there would be no statistical justification for needing an emergency ascent escape system just as commercial airliners don’t have such systems. (As I will discuss in Part 3, NASA had the opportunity to develop such a system.) Historically, space launch rockets have a launch failure rate around two to three percent. For example, the October 2018 launch of the crewed Soyuz experienced an ascent rocket failure, initiating an emergency separation and recovery of the capsule. By accepting proposals for systems that were not fully reusable, the need for an ascent escape system was imposed by NASA’s “human-rated” requirements. NASA’s decision to accept such proposals was, apparently, an implementation of their core willingness to accept “a certain level of risk” substantially worse than that of an airworthiness certified system.

Using the historical rocket launch failure rate, the probability of a rocket failure would be around 1 in 50. Without an ascent escape system, the crew would, of course, be lost. Hence, the purpose of the ascent escape system is to boost the LOC probability to a minimum acceptable risk. As NASA said after the Crew Dragon test incident, individual SuperDraco modules had been tested hundreds of time. (New jet engines are similarly tested, often for thousands of hours simulating a wide variety of flight and engine conditions, including bird ingestion.) What the accident showed was that spacecraft incorporated elements not previously tested in the flight configuration, contained parts that had critical but undetected flaws in the as-manufactured condition, were damaged during installation or handling, and/or suffered from a previously unknown failure mode. Hopefully, the accident investigation will identify the cause.

With the destruction of the Crew Dragon spacecraft in the April test, my understanding is that the capsule being built for the Demo 2 mission, which was to fly the first humans to the ISS, will now be used for the uncrewed ascent escape system test. It is possible that, after any needed changes or added inspections are identified, the SuperDraco engines will also be ground static test fired before the flight test. If these two tests are successful, then the Crew Dragon “type design” will have been shown by ground and flight testing to meet this part of NASA’s human-rated requirements—provided the minimum analytical probability LOC remains better than 1 in 270.

As will be discussed in Part 2, once an aircraft’s type design is approved and production begins, flight acceptance testing of each production aircraft is independently conducted to ensure it is airworthy before being operationally used. Only then is an airworthiness certificate issued for each aircraft. At that point, the probability of a serious accident is very low—which is why airliners, or the Orion III spaceliner, do not have emergency in-flight escape systems. Contrast this with the clear need of the commercial crew vehicles to have an ascent escape system due to the rocket having a likelihood of 1-in-50 or so of failure. Also, unlike each production aircraft, the flightworthiness of each rocket and capsule system will not be tested prior to its operational use.

In 2017, commuter aircraft in the United States—operationally equivalent to commercial crew spacecraft—suffered a serious accident in one in around 80,000 flights, with one fatality in roughly 600,000 flights. (At this commuter fatality rate, the Crew Dragon could transport more than two million people to space without a fatality.) The major airlines suffered no fatalities that year despite flying more than nine million flights. This is an indication of the statistical difference between NASA’s “human-rated” approach to achieving the “safest practical system that accomplishes the mission within constraints” and airworthiness that achieves true acceptable safety.

Space Safety Institute proposal

Several months ago, the International Association for the Advancement of Space Safety and, primarily, the International Space Safety Foundation proposed to the federal government the formation of a Space Safety Institute (SSI) to certify commercial human spaceflight safety. (Note that the proposal also uses the term “passenger” when discussing future commercial spaceflight.) I was surprised when a copy of the proposal was not made available to the public. Following my Freedom of Information Act request, the federal government provided the version they had been given. (The version of the proposal I received appears to be a draft dated March 2019, which is just prior to the Crew Dragon test accident.)

The foundation proposes to approach commercial human spaceflight safety certification as is now done for many commercial products involving human safety, with some form of safety certification provided through a non-government body.

The purpose of this report is to provide the rationale for the establishment of a (commercial) Space Safety Institute in the U.S. as “regulated self-policing” entity. It would be an open consortium of industry, space agencies and regulators to efficiently perform standardization and certifications activities, conduct joint research, and provide educational and professional training opportunities, within a broad framework of mandated policies and rules…

The proposed Space Safety Institute builds on concepts, experience and practices of various programs and sectors and may be archetypal of future direction in other fields (e.g. aviation)…

In conclusion, the Space Safety Institute would support a regulatory model that can react quickly and efficiently to technological advancements while exercising effective controls on commercial space systems developments. The Space Safety Institute would perform standardization and system certification activities, as well as educational and research activities. The regulator would establish broad policies and keep a general oversight role of institute’s processes and activities, while concentrating on other issues, which lie outside the Space Safety Institute scope, as space traffic management and international coordination.

The Space Safety Institute proposal would make NASA’s approach to assuring astronaut spaceflight safety the basis for their certification processes.

Safety policy and technical standards used by NASA Crew Commercial Program represent an excellent reference from which U.S. commercial human spaceflight industry can develop policies and standards to be used on non-NASA suborbital and orbital commercial spaceflight programs. Furthermore, industry can use the NASA CCP certification program as model for developing their own independent third-party certification process. [Emphasis added]

The proposal’s inference that NASA’s safety standards are “excellent” prompted my previous lengthy discussion of how I see the adequacy of NASA’s “human-rated” safety requirements. Obviously, I do not agree that NASA’s approach is excellent. Especially, I do not believe that it is a suitable model for commercial passenger spaceflight systems.

What the proposed Space Safety Institute would do

The proposal states:

The SSI main mission would be to establish and manage a safety certification process for commercial human rated systems which is lean, effective, and does not stifle innovation. A process that allows maximum design freedom and quick and efficient reaction to technological advancement.

A careful reading of the SSI’s mission shows that certifying only systems with demonstrated acceptable safety is neither mentioned nor implied in this brief mission statement. Instead, the foundation argues to adopt the NASA human-rated approach as the logical basis for “A process that allows maximum design freedom and quick and efficient reaction to technological advancement.” I interpret this as the foundation arguing that safety must play second fiddle to technological advancement. Is this really needed?

The British and French developed the ground-breaking Concorde supersonic airliner in the 1960s within the commercial airworthiness regime. This was less than 20 years after the first supersonic flight. (We are now nearly 40 years after the first Space Shuttle flight.) Boeing developed their substantially all-composite 787 airliners within the same airworthiness certification regime. Today, many companies are developing piloted and unpiloted commercial passenger flying taxis within the FAA certification regime.

Experience in the real world of aeronautics shows that making safety a priority fits well within a disciplined and well-structured system engineering development program. Airworthiness certification does not stand in the way of progress, but actually lubricates the gears driving progress forward by minimizing operational risk and encouraging future investment, just as is now happening with flying taxis.

The Space Safety Institute’s role, sitting between the regulatory entity—the FAA—and private industry will need to be defined, probably through legislation.

The Space Safety Institute would be somehow a “middle-man” between the regulatory body and the commercial space companies for the benefit of both parties. The SSI would provide standardization and safety certification services as a “recognized organization” approved by and operating under oversight of the regulatory entity.

A part of the institute’s organization would be a Safety Review Panel. Here is how the proposal identifies the panel’s role:

The SSI Safety Review Panel (SRP) will be responsible for conducting flight safety reviews. The SSI SRP will assist the developer/operator in assuring that safety critical systems, subsystems and operations are appropriately designed and verified. Specifically, the SSI Safety Review Panel will perform the following functions:

1. Assisting the developer/operator in interpreting safety requirements in a manner consistent with applicable requirements, and providing recommendations for implementation.
2. Conducting safety reviews as ap¬propriate during various phases of system development and operation.
3. Evaluating changes to system that either affect a safety critical sub¬system or create a potential hazard to interfacing systems, or crew.
4. Evaluating safety analyses and safety reports, and processes Non-Compliance Reports.
5. Ensuring the resolution of system safety issues.

At the successful conclusion of safety reviews cycle, the SSI Safety Review Panel Chair would submit a Certificate of Flight Readiness (CoFR) to the regulatory organization (FAA). [Emphasis added]

A key element of the panel’s proposed responsibility is “assuring that safety critical systems, subsystems and operations are appropriately designed and verified.” If the intent is to verify that each production system is demonstrated to be flight-worthy by independent operational testing, as is done with aircraft, then the panel is just undertaking the FAA’s governmental role in verifying airworthiness. In such a case, what is the value added of the SSI? Shouldn’t the FAA be organically capable of doing this?

If, instead, the Institute’s intent is to adopt NASA’s “human-rated” approach where independent operational testing of each production system is not needed in order to obtain a Certificate of Flight Readiness, then what real value would such a certificate have? The SRP’s certification appears to just become a checklist, not an independent flight-worthiness verification that would establish public confidence in the use of each operational system used for commercial passenger spaceflight services.

I conclude that the Space Safety Institute proposal is not an effective substitute for the federal government’s organic responsibility to ensure the acceptable safety of commercial passenger spaceflight, just as the government does for commercial air travel. Further, I believe the term “human-rated” should be banned from use when discussing commercial human spaceflight safety. It is totally misunderstood by the public and is, especially, misleading to those being asked to make an “informed decision” about their personal safety.

Segregate the commercial passenger spaceflight regulatory path going forward from NASA

NASA was created in 1958 to separate human spaceflight from military space activities at a time when Cold War tensions were very high. President Eisenhower, for several reasons, did not want any public focus on highly secret military space programs, primarily being undertaken by the Air Force, to enable satellite observation of the Soviet Union and to build an effective nuclear missile deterrent capability. The threat of a nuclear “Pearl Harbor”—first with bombers and, later, with ballistic missiles—drove Eisenhower’s national security priorities throughout most of his administration.

President Kennedy, also for various reasons, gave NASA a political shot of financial adrenaline with his human lunar landing challenge. Only months into office, and after both the Cuban Bay of Pigs fiasco and the Soviets putting a human into orbit, he needed a political win. He decided to literally shoot for the Moon. Billions flowed to NASA and its contractors to make this happen.

Not disparaging the substantial technological and scientific accomplishments made by NASA, it has become a political juggernaut. Despite plainly stupid decisions costing lives and limiting commercial space development, it is sustained by Congress persistently funneling non-military aerospace money to favored Congressional districts and states. That Congress has consistently acquiesced to NASA’s misleading “human-rated” approach to safety establishes the true unimportance of astronaut safety to Congress. That, in 2004, after the loss of Columbia, Congress legally made commercial human spaceflight participant safety also unimportant reinforces this conclusion.

What is OK for NASA is not necessarily good for everyone else when it comes to safety. Despite the clearly apparent dangers of NASA human spaceflight, it has no shortage of the bold and brave seeking the glory and rewards of becoming a NASA astronaut. More than 18,000 people applied to become NASA astronauts in the most recent application cycle. What has made this approach politically work for NASA has been the extremely low flight rate of NASA’s human missions, combined with the hero worship of astronauts, especially by children. When only a handful of missions are undertaken a year, as the Space Shuttle experience demonstrated, failures are sufficiently infrequent that Congress, after appropriate public handwringing, forgives and forgets so that the money can keep flowing to key Congressional districts and states. Meanwhile, the clear lack of safety makes meaningful conventional commercial investment unwise.

Given these circumstances, setting NASA apart and letting NASA handle its astronaut safety as Congress permits is appropriate. Congress holds NASA’s purse strings and, thus, controls NASA’s safety morality. However, proposing to use NASA’s commercial crew approach to safety as their “model for developing their own independent third-party certification process” for commercial passenger spaceflight is fundamentally unethical and the fatal flaw in the foundation’s Space Safety Institute proposal. True commercial passenger spaceflight will involve much higher flight rates requiring much, much lower analytical probabilities of loss of life. Acceptable commercial passenger spaceflight safety will not arise from NASA’s inherently broken safety system. Instead, we must turn to what has worked for air travel and extend this to all commercial passenger spaceflight: the hands-on federal government regulation of commercial passenger spaceflight systems to establish their airworthiness.

• 

(ed note: there was a news story about how the Volkswagen company was selling diesel automobiles containing a "defeat device" used to fraudlently pass emissions testing)

Tobias Klausmann

     This got me thinking: in an SF universe with spaceships (and possibly FTL), there probably is minimum standard for what is allowed to zip around at kilometers per second, as soon as space stations and the like are involved. Who does the certification? Even if there isn't an official body that tries to keep everyone safe, there will be a consensus, however muddy, about what (not) to do.
     When steam engines proliferated around the industrial revolution, there were quite a few horrendous boiler explosions, leading to the formation of standard bodies that would certify (and spot check, after initial approval) boilers.*
     Naturally, enforcing these standards is very difficult, especially if ad-hoc repairs are somewhat common on long missions. What you flew out with may have been certified, but what you came back with is just a mess of chicken wire and duct tape.
     In the case of only grass-roots "standardization", justice for endangering others with your hunk o' junk may be swift and airlock-shaped.

     * Historical side note: The organization that (among other things) checked vehicles for road safety in Germany (TÜV) was a descendant of such an organization (DKÜV, Dampfkesselüberwachungsverein, boiler inspection association), but these days there are various orgs that do this.

• 

Ron Fischer

     Border or port inspections. Out system you'd be on your own, but as you got nearer populated colonies or Earth you'd be boarded for an inspection, before proceeding. If I may say so this feels like a GREAT idea for some stories. Basically "Customs Police" in space.

Tobias Klausmann

     This naturally hinges on how the drive systems work. With choke points (like jump gates), this is easy, but with arbitrary-location jump drives, this becomes tricky. Naturally, arbitrary jump points are also a strategic nightmare, unless you can somehow see them coming, like jump-pre-echoes, for example.
     A problem I see with arrival inspections is that most ships can not be thoroughly inspected without a dock, and even then, testing all the fail-cutout machinery could easily take weeks, so short of having those components sealed, I don't see this as feasible, unless travel times are already in the neighborhood of months.
     It's also a question of system throughput: in a place where a hundred ships arrive a day and an inspection takes at least two days, you need an enormous amount of manpower to just do checks. And this manpower needs to be away from stations/ports, and thus becomes quite expensive.

Ron Fischer

     Interesting points. I wonder how its done now? Some of the inspection is done at the port of departure or even when a container is closed, no?

Tobias Klausmann

     There is a huge discrepancy between the two trades that come to mind first: aircraft and ships. For the former, airworthiness is a serious cost factor and it is baked into the manufacturing process of aircraft. For the latter, nobody gives a sh*t until something happens.
     The thing with space craft on mid- to long-haul service is that modification will probably be much more common. In a sense, they bridge the gap: they are as dangerous-delicate as aircraft, yet have away-from-port times as long as ships do (possibly longer).
     The problem is: a pilot is not expected to repair the aircraft mid-journey and there is often (but not always) a place to go in emergencies. A ship does not have that luxury, which, combined with a "healthy" dose of tradition and business sense means that repairs underway are somewhat common. The basic idea seems to be: if it floats, is not on fire or carrying disease, we're good.
     I am not sure how to solve the discrepancy when it comes to spacecraft. 

• 

Before owning a car became typical, roads and highways (the few that existed) were never crowded. It was only after everyone started purchasing and driving their own vehicles—to work, school, even the grocery store around the block—that streets grew congested, rush hour became an everyday occurrence, and car accidents became an inevitability.

Space, despite its vastness, could be on a similar trajectory. With so many new flying objects being sent into orbit and beyond, many scientists say, we could be in for some dangerous collisions. One group at Los Alamos National Laboratory in New Mexico is trying to fix that with something ubiquitous among cars, but currently nonexistent for space mobiles: A license plate.

It’s unlikely we’ll ever fill our cosmic neighborhood with enough flying objects to create anything like a space traffic jam, where satellites have to slow down at specified times or travel in their own intergalactic lanes. But space, in all its low-to-no-gravity glory, poses its own challenges.

The majority of satellites and other fancy objects we send into the cosmos stay in low Earth orbit (LEO), around 400 to 1,000 miles above Earth’s surface. It’s far enough away from the planet’s gravitational pull, but not too far; this sweet spot lets an object orbit pretty much indefinitely without needing much help.

But scientists have taken advantage of this prime parking space for the past 60 years, so debris is starting to build up. There’s more space junk on the way, too. As of 2015, there are more than 1,300 active satellites orbiting the Earth. That’s in addition to the inactive ones, as well as old rockets and other defunct space junk stuck in LEO indefinitely. That’s likely to increase exponentially with the introduction of CubeSats, miniature spacecraft that can be sent into space by the hundreds, and the various companies that plan to install internet-providing satellites in the LEO. What a space jam.

But don’t things just float around up there like a giant game of bumper cars? Not even close, explains David Palmer, an astrophysicist at Los Alamos. While there have only been two really substantial space crashes, he says, one crash is all it takes to trigger catastrophe.

“The problem is that once you have one collision, it makes a lot of debris, and that debris can then collide. Eventually you get what’s called the Kessler effect,” he says. Debris keeps building up with each new collision, creating infinitely more crashes. If this begins to happen on a regular basis, it’s possible for so much space junk to accumulate that space itself becomes unsafe.

“We are close to the point where if we keep on going for a little while longer, we will be pushing over the edge,” he says. “Once that starts happening, it can progress for a decade or two until there is too much debris in low Earth orbit.” At that point, the chances of a collision (and subsequent Kessler effect) become so high that the benefits of sending another satellite into LEO don’t outweigh the risks.

The big problem is when satellites retire. While in use, nearly all have GPS devices that scientists can use to find them with radio signals. But once satellites are out of commission, so are those radio waves. The space junk just orbits, without monitor, indefinitely. If an active satellite seems like it’s going to collide with one of them, the owner can dodge out of the way. But once a point is reached where space junk is just colliding with space junk, researchers can’t move either bodies out of the way without an owner’s permission. And to know who it belongs to, you first need to know what the object is. “You would need the permission of the satellite owner even if it’s a 30-year-old piece of space junk,” says Palmer. There has to be another method—a foolproof identification system. That’s how Palmer sees it.

His past research studying pulsars gave him an idea. Pulsars are large space objects that spin and emit beams of light in opposing directions. As they spin their light beams appear to flicker, and scientists, like Palmer, have put a lot of effort into studying that flickering.

“I put those two things together and thought that if I could create a satellite that produced a periodic signal,” says Palmer, “then by reading that signal, we could create an accurate identification system.

So Palmer and his team developed a super-low-power, miniature device that emits a unique pattern of blinks in the form of a laser. They call it Extremely Low Resource Optical Identifier (ELROI) or, more casually, space license plates.

Meant to be about a square inch by square inch, these devices would sit atop any satellite bound for space. Using a laser diode (what many everyday lasers are made of), the device would emit a series of very short red laser pulses. These flashes would be extremely bright (as bright as a 60 watt bulb, from something that uses only one watt of total power), and would continuously flash a series of specific pulses for no more than a millionth of a second. It would then shut off for a thousandth of a second—a thousand times as long as it was on for. A telescope on Earth could pick up that series of flashes, and with the help of a computer program, decipher what specific satellite it was coming from.

Despite the satellite being hundreds of miles away from the ground, the message is still crystal clear, explains Palmer. The light is coming from a laser and is the exact wavelength of the color red. A filter in the telescope blocks out all other wavelengths, allowing that color to shine through. The blinking corresponds to a binary (composed of hundreds of 1s and 0s) serial number. Each satellite, like a car, gets its own serial. The code tells the identifier three things: The kind of satellite it is, who owns it, and the path of its orbit.

The goal, says Palmer, is to have the devices sit on satellites and remain powered for at least 25 years, if not indefinitely. The the device uses a huge percentage of its battery’s life during its split second of blinking, but then spends a thousand times longer charging with solar energy. It can do this repeatedly, says Palmer, for about 25 years. Palmer thinks the device will be able to run off of its solar cells indefinitely even after the battery dies, but it’s impossible to be sure.

Their next goal is to actually test the prototype. They plan to do so by working with a team at New Mexico Tech who are sending a CubeSat into space this coming January. CubeSats, says Palmer, are an ideal vessel to test the device on: They are tiny, 10 centimeter cubed satellites that can be sent up into LEO, often en masse, to perform small experiments.

Though the prototype is ready for a test launch, Palmer says, the researchers are still tweaking the design. The ELROI is currently about four square inches and one inch thick. In the future, the team wants to get it down to the size of a postage stamp, and use materials such that the entire thing costs under $1000. That way, he says, even a high school science class can afford to send one up to low Earth orbit. CubeSats' low cost (one can cost only $10,000 to build; launching them into space is a few tens of thousands more) means they can be used by small, private companies, university students, and even high schoolers. Make the license plate price any higher, says Palmer, and, “that’s a lot of cakes you would have to sell at the bake sale.”

With the license-plated CubeSats up in space, the researchers will attempt to identify the miniature spacecraft by pointing a telescope at them and translating the binary code. If all goes according to plan, the goal is to test them on bigger satellites, with the ultimate objective to get them on every satellite that enters space.

Palmer admits that ELROIs are not a perfect solution. If two satellites are indeed colliding, you still need to ask for permission from the abandoned space junk’s owner before you remove it from orbit. If there isn’t enough time to track that person down, knowing who they are might not help you avoid disaster. But identifying who owns the aged space junk is indeed a good first start. It might not be too long before low-Earth orbit looks more like a busy highway than a vast, endless entity. And then people may wonder how breezy that open road must have been, back before satellites needed laser-powered license plates.

If modular design is taken to its limit, "ships" will have no permanent existence. Instead they will be assembled out of modules and pods specifically for each run, much like a railroad train.

In that case, a ship's identity is attached to a service, not a physical structure. Example: the Santa Fe "Chief" was identified by a timetable and reputation, not a particular set of locomotive and cars.

(ed note: Veyndayk, Velmeran, Dveyella, and Keth are Starwolves. They are in the business of capturing warships of the stodgy bureaucratic interstellar Union and selling said warships back to the Union.)

     Soon they saw that it was Veyndayk, the cargo supervisor.
     "Business done," he said, stepping up to join Velmeran and Dveyella at the rail where they had been watching traffic pass on the level below.
     "Did you sell Keth back to the Sector Commander?" Velmeran asked.
     Veyndayk laughed. "No, although that might be a good use for old Starwolves. Farstell Freight and Trade bought back a shipment of clothing, conveniently packed in their own shipping containers. And (Union) fleet ordnance has just now payed us a finder's fee for an intact cutter."
     "A cutter?" Velmeran asked. Cutters were the smallest of the military ships, hardly bigger than a transport, and generally used only for police work.
     "My little joke," Veyndayk explained. "We took two intact cutters as riders on salvaged battleships, and one we have had sitting in a forward bay for the last year. We took them apart down to the smallest bolt and rebuilt the ships by taking parts at random. Now I am going to collect finder's fees on those ships in three different ports. That should give the boys in fleet ordnance fits, when they cross-check serial numbers of those parts."
     That appealed to Dveyella, who liked frustrating Union officials best of all. "You know, they will not be able to use those ships until they take them apart and rebuild them as they originally were."
     "You laugh, but that is probably the truth," the cargo officer said.

• 

With the advent of lunar exploration and round trip lunar transport, both chemical and nuclear, there inevitably will arise malfunctions and emergencies. There will arise communication difficulties, navigational errors, propulsion breakdowns, and structural failures. There are possibilities of collisions between spacecraft and of fatal damage from matter in space. More likely, however, are onboard concerns of life-support malfunctions, auxiliary power irregularities, compartment over pressurization (in some cases, explosions), cargo shifting, and unforeseen disorders. These are the realities of increased space travel.

In anticipation of spaceflight realities, there would be need for a nuclear rescue ship operating in translunar space. The primary role of such a ship would be to save human life and those extraterrestrial specimens aboard any ill-fated lunar vehicle. A secondary role would be to salvage the spacecraft if at all possible.

This means that the rescue ship would require propulsive capability to drastically change orbit planes and altitudes. It would require excess ΔV to proceed with dispatch to rendezvous with a disabled spacecraft. In addition, capability would be required for transferring personnel and equipment, making repairs to a disabled vehicle, and even taking it in tow if conditions warranted. The latest advances in crew facilitation, passenger accommodations, repair shops, navigational devices, and communication equipment would be required. As an introductory concept, one arrangement of a nuclear rescue ship is presented in Figure 11-11 (see above).

A particular feature to note in Figure 11-11 is the use of two nuclear engines. Each engine would be of the lunar ferry vintage and, therefore, would be sufficiently well developed and man-rated for rescue ship design. These engines would be indexed by a nominal I_sp of 1000 seconds; they would have a short time overrating of, perhaps 1100 seconds. This overrating implies conditional melting of nuclear fuel in the reactor for emergency maneuvers and dispatch.

A rescue ship would be characterized by a large inert weight compared to a regular transport vehicle. This means that large magnitudes of engine thrust would be required. However, during periods of non-emergencies, low thrusts could be used. The vehicle F/W_o characteristics (Thrust-to-weight ratio) would vary over a wide range: possibly from 0.1 during non-emergencies to 1 during emergencies. Two engines would provide the high thrust capacity for emergencies. During non-emergencies, one engine could be left idling; the other engine could provide low thrust for economic cruise. Furthermore, two engines would provide engine-out capability for take-home in the event of malfunction in one of the engines. For reactor control reasons, the two reactors would have to be neutronically isolated from each other. For this purpose, note the neutron isolation shield in Figure 11-11.

(ed note: Nuclear reactors are throttled by carefully controlling the amount of available neutrons within the reactor. A second reactor randomly spraying extra neutrons into the first reactor is therefore a Bad Thing. "Neutronically isolated" is a fancy way of saying "preventing uninvited neutrons from crashing the party." Related term is "Neutronic Decoupling")

• 

A suggested patrol region for the rescue ship is indicated in Figure 11-12 (see above). Note that a rendezvous orbit has been designated so that the rescue ship could replenish its propellant from the nuclear lunar transport system. By having rendezvous missions with nuclear ferry routes, rescued personnel, lunar specimens, and damaged spacecraft parts could be returned to Earth without the need for the rescue ship returning. Also, rescue ship crew members could be duty-rotated this way. This would increase the on-station time of a nuclear rescue ship.

• 

• 

• 

• 

Orbital Patrol Ship

Stats
Propulsion	Chemical H2-O2
Exhaust Velocity	4,400 m/s
Specific Impulse	449 s
Thrust	3.5×106 N
Thrust Power	7.7 gigawatts
Total ΔV	6,100 m/s
Mass Budget
Engine Mass	7 mton
Heat Shield Mass	15 mton (15% re-entry mass)
Terra Recovery parachute, retro, landing gear	5 mton (5% landing mass)
NonTerra Recov landing legs Luna, Mars	5 mton (5% landing mass)
Misc attitude jets, electrical, etc.	20 mton (20% dry mass)
Aerodynamics controls, farings, etc.	5 mton (5% dry m)
Tankage body	18 mton (6% of 300 mton H2-O2)
INERT MASS	75 mton
Payload, hab module cargo bays	25 mton
DRY MASS	100 mton
Propellant H2-O2	300 mton
WET MASS	400 mton
Mass Ratio	4.0
Plus booster rocket	? mton

This is a splendid spacecraft designed by Rick Robinson, appearing on his must-read blog Rocketpunk Manifesto. This was designed for his Orbital Patrol service, which he covered in three previous posts.

The important insight he noted was that if you can somehow get your spacecraft into orbit with a full load of fuel/propellant, it turns out that most cis-Lunar and Mars missions have delta V requirements well within the ability of weak chemical rockets. So you make a small chemical rocket and lob it into orbit with a huge booster rocket (heavy lift launch stack). This will be the standard Orbit Patrol ship.

It can also be boosted into orbit by a smaller booster rocket, then using the patrol ship's engines for the second stage. So as not to cut into the ship's mission delta V, it will need access to an orbital propellant depot to refuel. At a rough guess, you'll need 9,700 m/s delta V to boost the patrol ship into orbit (7,900 m/s orbital velocity plus gravity and aerodynamic drag losses). So the booster will need 9,700 m/s with a payload of 400 metric tons. Bonus points if the booster is reusable.

Actually, it reminds me a bit of the old Three Man Space Scout.

---

At a rough guess, Rick figures that if the ship is capsule shaped it will be about 12 meters high by 14 meters in diameter. If it is wedge shaped, it will be about 40 meters high by 25 meters wide by 8 meters deep.

In both cases, total interior volume of 1,200 m³ (of which 900 m³ is propellant), and a surface area of 800 m²

---

Present day expandable propellant tanks have a mass of about 6% of the mass of the liquid propellant. Rick is assuming that in the future the 6% figure will apply to reusable tanks as well.

If my slide rule is not lying to me, the 300 metric tons of H₂-O₂ fuel/propellant represents 33.3 metric tons of liquid hydrogen and 266.7 metric tons of liquid oxygen. About 470 m³ of liquid hydrogen volume (sphere with radius of 4.8 m) and 234 m³ of liquid oxygen volume (sphere with radius of 3.8 m). This is a total volume of 704 m³ which falls short of Rick's estimate of 900 m³ so I probably made a mistake somewhere.

---

Landing on Terra will use retro-rockets, the heat shield for aerocapture, maybe a parachute, and aircraft style landing gear for belly landing. Landing on Luna or Mars will be by tail-landing on rear mounted landing legs. That will also mean reserving some of the propellant for landing purposes.

Note that the heat shield is rated for the ship's unfueled mass (heat shield mass = 15% of ship's re-entry mass), there is not enough to brake the ship if it has propellant left. This assumes a "low-high'low" mission profile: start at LEO, go outward to perform mission while burning most of the propellant, then return to LEO or even land on Terra. So 15 metric tons for heat shield is for a ship with a mass of 100 metric tons at re-entry (ship's total dry mass).

If the ship is going to aerobrake then return to higher orbit, it will need more heat shield mass to handle the extra mass of get-home propellant. This will savagely cut into the payload mass, which is only 25 metric tons at best. For example, if the mission had the ship heading for translunar space from LEO after aerobraking, the extra propellant mass at aerobrake time will increase the heat shield mass from 15 metric tons to 31. This will reduce the payload from 25 metric tons to 8. But by the same token a ship that will not perform any aerobraking can omit the heat shield entirely, using the extra 15 metric tons for more propellant or payload.

---

Payload includes habitat module (if any) as well as cargo, since hab modules are optional for short missions. The gross payload is 25 metric tons, of which 20 is cargo and the other 5 mtons are payload bay structure and fittings. If you assume two tons of life support consumables per crew per two week mission; then the ship could carry a crew of five plus 12 mtons of removable payload, or a crew of 10 and 4 mtons of payload (the more that payload is consumables, the less mass needed for payload bay structure).

---

Patrol Missions

Mission	Delta V
Low earth orbit (LEO) to geosynch and return	5700 m/s powered (plus 2500 m/s aerobraking)
LEO to lunar surface (one way)	5500 m/s (all powered)
LEO to lunar L4/L5 and return (estimated)	4800 m/s powered (plus 3200 m/s aerobraking)
LEO to low lunar orbit and return	4600 m/s powered (plus 3200 m/s aerobraking)
Geosynch to low lunar orbit and return (estimated)	4200 m/s (all powered)
Lunar orbit to lunar surface and return	3200 m/s (all powered)
LEO inclination change by 40 deg (estimated)	5400 m/s (all powered)
LEO to circle the Moon and return retrograde (estimated)	3200 m/s powered (plus 3200 m/s aerobraking)
Mars surface to Deimos (one way)	6000 m/s (all powered)
LEO to low Mars orbit (LMO) and return	6100 m/s powered (plus 5500 m/s aerobraking)

---

For a representative samples of small space craft atop booster rockets go here.

• 

The 2009 satellite collision was the first accidental hypervelocity collision between two intact artificial satellites in low Earth orbit. It occurred on February 10, 2009, 16:56 UTC, when Iridium 33 and Kosmos-2251 collided at a speed of 42,120 km/h (11.70 km/s; 26,170 mph) and an altitude of 789 kilometres (490 mi) above the Taymyr Peninsula in Siberia.

Collision

The collision destroyed both Iridium 33 (owned by Iridium Communications Inc.) and Kosmos 2251 (owned by the Russian Space Forces). The Iridium satellite was operational at the time of the collision. Kosmos-2251 was launched on June 16, 1993, and went out of service two years later, in 1995, according to Gen. Yakushin. It had no propulsion system, and was no longer actively controlled.

Several smaller collisions had occurred previously, during rendezvous attempts or the intentional destruction of a satellite, including the DART satellite colliding with MUBLCOM, and three collisions involving the manned Mir space station, during docking attempts by Progress M-24, Progress M-34, and Soyuz TM-17, but these were all low-velocity collisions. In 1996, the Cerise satellite collided with space debris. There have been eight known high-speed collisions in all, most of which were only noticed long after they occurred.

Fallout

U.S. space agency NASA estimated that the satellite collision created approximately 1,000 pieces of debris larger than 10 centimeters (4 inches), in addition to many smaller ones. By July 2011, the U.S. Space Surveillance Network had cataloged over 2000 large debris fragments. NASA determined the risk to the International Space Station, which orbits about 430 kilometres (270 mi) below the collision course, to be low, as was any threat to the shuttle launch (STS-119) then planned for late February 2009. However, Chinese scientists have said that the debris does pose a threat to Chinese satellites in Sun-synchronous orbits, and the ISS did have to perform an avoidance maneuver due to collision debris in March 2011.

By December 2011, many pieces of debris were in a steady orbital decay towards Earth, and expected to burn up in the atmosphere within one or two years. By January 2014, 24% of the known debris had decayed. In 2016, Space News listed the collision as the fourth biggest fragmentation event in history, with Iridium 33 producing 628 pieces of cataloged debris, of which 364 pieces of tracked debris remain in orbit as of January 2016.

A small piece of Kosmos 2251 satellite debris safely passed by the International Space Station at 2:38 a.m. EDT, Saturday, March 24, 2012. As a precaution, the six crew members on board the orbiting complex took refuge inside the two docked Soyuz rendezvous spacecraft until the debris had passed.

A number of reports of phenomena in the US states of Texas, Kentucky, and New Mexico were attributed to debris from the collision in the days immediately following the first reports of the incident in 2009, although NASA and the United States Strategic Command, which tracks satellites and orbital debris, did not announce any reentries of debris at the time and reported that these phenomena were unrelated to the collision. On February 13, 2009, witnesses in Kentucky heard sonic booms. The National Weather Service issued an information statement alerting residents of sonic booms due to the falling satellite debris. The Federal Aviation Administration also released a notice warning pilots of the re-entering debris. Some reports include details that point to these phenomena being caused by a meteoroid shower. A very bright meteor over Texas on February 15, 2009, was mistaken for reentering debris.

Cause

Events where two satellites approach within several kilometers of each other occur numerous times each day. Sorting through the large number of potential collisions to identify those that are high risk presents a challenge. Precise, up-to-date information regarding current satellite positions is difficult to obtain. Calculations made by CelesTrak had expected these two satellites to miss by 584 meters.

Planning an avoidance maneuver with due consideration of the risk, the fuel consumption required for the maneuver, and its effects on the satellite's normal functioning can also be challenging. John Campbell of Iridium spoke at a June 2007 forum discussing these tradeoffs and the difficulty of handling all the notifications they were getting regarding close approaches, which numbered 400 per week (for approaches within 5 km) for the entire Iridium constellation. He estimated the risk of collision per conjunction as one in 50 million.

This collision and numerous near-misses have renewed calls for mandatory disposal of defunct satellites (typically by deorbiting them or at minimum sending them in graveyard orbit), but no such international law exists yet. Nevertheless, some countries have adopted such a law, such as France in December 2010. The United States Federal Communications Commission (FCC) requires all geostationary satellites launched after March 18, 2002, to commit to moving to a graveyard orbit at the end of their operational life.

• 

• 

SECRET YELLOW / EYES ONLY OMRD

PROJECT TAR BABY

PROPOSAL

A prohibitive constraint on the use of conventional weapons in the anti-satellite (ASAT) role is their tendency to create debris through a variety of paths: direct ablation, spallation or fragmentation debris, warhead shrapnel, non-intercepting ordnance, and so forth.

The accumulation of such debris beyond a chaotically variable critical point – easily surpassed during military escalation, per Orbital Hazards in Simulated Great Power Escalation Scenarios (Oricalcios, Efiathe, and Cylassé, 2074) – poses a long-term hazard to civilization by inducing a cascade catastrophe, a rapid chain multiplication in debris count likely to render the orbital bands involved non-viable in the long term.

TAR BABY attempts to avert this by developing a specialized non-fragmentation ASAT weapon.

Specifically, we propose a dedicated ASAT warhead designed for compatibility with the Firehawk surface-to-orbit missile system (selected for its multiple-burn capability). Upon closing with the target satellite, this warhead deploys a sphere of viscous adhesive at its nose, formulated to remain effective in vacuum conditions for the duration of the impact event and to retain its shape via surface tension.

It is believed that this mechanism should allow a TAR BABY warhead to achieve a hard connect with the target satellite with minimal uncaptured fragmentation. Embedding within the adhesive body should in itself cause significant disruption to the operation of the target, but for maximal effect, after the adhesive sphere has set (either by passage of time or injection of a catalyst), the multiple-burn capability of the Firehawk can be used to perform a controlled deorbit and destruction of the captured satellite.

For further details of our proposal, please see the enclosed technical documentation.

Submitted for your consideration,

Vidal Amnestrianos

for and on behalf of

Firefly Aerospace, ICC

PROLOGUE—THE KESSLER SYNDROME

(ed note: the following is real)

1978—NASA Scientist, Donald Kessler, predicts that the density of space junk in Low Earth Orbit or LEO will eventually reach a critical mass such that the random collision rate will exceed the orbital decay rate—not unlike a nuclear chain reaction. Objects in LEO maintain orbital speeds of over 26,000 kilometers/hour, enough kinetic energy for a 1-kg piece of debris to destroy a 1000-kg satellite costing hundreds of millions of dollars. Such a collision would shatter the satellite into hundreds more fragments that go on to strike still more targets. If this phenomenon is unmitigated, the collision rate will hit a tipping point, exponentially reducing the life expectancy of new satellites until space is no longer be commercially viable.

1985—US F-15A fighter shoots down a 907-kg Solwind P78-1 research satellite with an antisatellite (ASAT) missile producing an undisclosed quantity of debris.

2006—USS Lake Erie Ticonderoga class missile cruiser shoots down USA-193 spy satellite with a RIM-161 Standard Missile 3 producing an undisclosed quantity of debris.

2007—Chinese Xichang Satellite Launch Center shoots down a 750-kg Fengyun FY-1C weather satellite with an SC-19 ASAT producing more than 3000 pieces of space debris.

2009—A 560-kg Iridium-33 communications satellite and a 950-kg Kosmos-2251 communications satellite collided producing a combined total of 1788 pieces of space debris.

2013—Chinese Xichang Satellite Launch Center tested an improved SC-19 ASAT missile capable of reaching medium earth orbit (MEO), highly elliptical orbit (HEO), and geostationary Earth orbit (GEO). There are no satellites orbiting Earth that are not vulnerable to ASAT attack.

(ed note: from this point on it is science fiction)

2022—NORAD publicly announces that without increased funding from Congress and the exponential increase in fragmentation and mission-related debris, it will in the future only attempt to track large spacecraft and rocket bodies.

2023—US Congress passes a bill stating that the role of NASA is as a risk-reduction agency for the commercialization of space, citing there is no further public demand for space exploration. Included in the bill is authorization to sell to private interests all NASA and Air Force facilities and equipment devoted to space launch, development, and science & exploration.

2024—Nuclear weapons, now commonplace among Second and Third world nations, are primarily seen as political immunity devices due to the international consequences of offensive use of nuclear weapons—the return of the Cold War’s Mutually Assured Destruction doctrine (MAD). As a result, rogue nations turn to shooting down derelict satellites in LEO in order to advertise their status in the global arena.

2028—The average lifespan of a satellite is now less than three months due to increasing density of space debris. Lloyd’s of London declares it can no longer insure satellites. Commercial operations in LEO cease.

2030—SpaceCorp initiates construction of the SpaceCorp Space Station SSS Werhner Von Braun, a one kilometer spinning ring advertised as the first debris-proof instrument-hosting space station.

2038—The Von Braun is christened. 45 astronauts are killed and 427 wounded by debris strikes during its eight-year construction.

• 

      Derelict satellites could in future be grappled and removed from key orbits around Earth with a space tug using magnetic forces.
     This same magnetic attraction or repulsion is also being considered as a safe method for multiple satellites to maintain close formations in space.
     Such satellite swarms are being considered for future astronomy or Earth-observing missions – if their relative positions can stay stable they could act as a single giant telescope.
     To combat space debris, interest is growing in plucking entire satellites from space. The biggest challenge is to grapple and secure such uncontrolled, rapidly tumbling objects, typically of several tonnes.
     Multiple techniques are being investigated, including robotic arms, nets and harpoons.

     Now researcher Emilien Fabacher of the Institut Supérieur de l'Aéronautique et de l’Espace, part of the University of Toulouse in France, has added another method to the list: magnetic grappling.
     “With a satellite you want to deorbit, it’s much better if you can stay at a safe distance, without needing to come into direct contact and risking damage to both chaser and target satellites,” explains Emilien.
     “So the idea I’m investigating is to apply magnetic forces either to attract or repel the target satellite, to shift its orbit or deorbit it entirely.”
     Such target satellites would not need to be specially equipped in advance. Instead, such a tug would influence target satellites using their ‘magnetorquers’: reliable electromagnets already carried to adjust orientation using Earth’s magnetic field.
     “These are standard issue aboard many low-orbiting satellites,” adds Emilien. 
     The strong magnetic field required by the chaser satellite would be generated using superconducting wires cooled to cryogenic temperatures.

     Similarly satellites could also keep multiple satellites flying in precise formation, comments Finn Ankersen, an ESA expert in rendezvous and docking, formation flight.
     “This kind of contactless magnetic influence would work from about 10–15 m out, offering positioning precision within 10 cm with attitude precision 1–2°.”
     For his PhD research, Emilien has been researching how the resulting guidance, navigation and control techniques would work in practice, combining a rendezvous simulator with magnetic interaction models, while also taking account of the ever-changing state of Earth’s own magnetosphere.

• 

     His research has been supported through ESA’s Networking/Partnering Initiative, which supports work carried out by universities and research institutes on advanced technologies with potential space applications. Emilien also visited ESA’s technical centre in the Netherlands, to consult with Agency experts.
     Emilien recalls that the concept originally came out of discussion with ESA experts, and he was lucky enough to be in the right place at the right time to explore its feasibility: “The first surprise was that it was indeed possible, theoretically – initially we couldn’t be sure, but it turns out that the physics works fine.”

• 

When it comes to space debris, the numbers are repeated often: more than 21,000 objects ten centimeters across or larger, approximately half a million objects between one and ten centimeters in diameter. Across the space community, there is general agreement that space debris is an existing, and worsening, problem. Many point to the free and open access to space, while others argue that proposed “megaconstellations” will take low Earth orbit to the breaking point. In response, some argue that economic disincentives, like orbit fees or taxes, could be used to reduce demand by increasing the cost of a satellite in orbit. Some argue that additional satellites create additional debris risk solely based on the increase in the satellite population. But is this the problem we are trying to solve?

The problem of space debris and congestion is not one of operational satellites, but rather one created by non-maneuverable debris. Space situational awareness and conjunction alerting systems seek to prevent collisions by maneuverable objects, further reducing the risk they impose. It is not the operational satellite, but the behaviors associated with putting the satellite in orbit and removing it at end of life, that increases the debris risk.

In developing appropriate mitigation strategies for orbital debris, it is imperative to consider the primary causes of orbital debris and develop approaches that address those causes. The principal sources of orbital debris are satellite explosions and collisions, including intentional destruction. High-risk orbital behaviors are well known: old launch vehicle upper stages left in orbit with residual propellants and high-pressure fluids, defunct satellites that are not deorbited, and anti-satellite weapons testing. These are the primary contributors to orbital debris and should be the focus of debris mitigation strategies.

State, commercial, and non-government users of space have a shared interest in creating the long-term sustainability of space operations, and global progress requires international agreement. Proposers for an orbital use tax mention that it would need to be globally harmonized but fail to recognize the difficulty in reaching such an agreement—if such an agreement is even possible. The recent collapse of the OPEC pact and the subsequent oil price war illustrates the fragility of international economic collaboration. By contrast, international agreements on standards and regulation for international operators, as we see in the maritime and aviation industries, tend to endure. It is important to recognize that diplomatic resources are limited and efforts to reach international agreement should focus on areas that can provide the most benefit and have the greatest chance for success.

For the long-term sustainability of space, the answer is not to make space more expensive to use, but rather to ask the users, both civilian and military, to be responsible to the goal of sustainable use. This requires a focus in three critical areas: collision avoidance, limiting debris-generating behaviors, and debris removal. As we ask the space community to be more responsible, it is important to define what that means. As illustrated by recent anti-satellite missile tests, the community can be alarmed, but we are functionally unable to hold each other to standards of behavior if those standards do not exist. Efforts at international agreement should be focused on reaching agreement in these areas if we are to have a sustainable and accountable orbital domain.

The space debris problem is complex and will not be solved by targeting one section of the industry. It is important to look at primary contributors to the problem. Leaving non-maneuverable objects in orbit creates an unresolvable collision risk as illustrated in January, when two intact satellites that had been in orbit for decades came within meters of colliding (see “Will we hit the snooze button on an orbital debris wakeup call?”, The Space Review, February 17, 2020). By contrast, days before the potential collision, a damaged DirecTV satellite at risk of exploding was maneuvered to a graveyard orbit where it did not pose a debris hazard to other operators. An orbital use tax would put an additional financial penalty on the user that is able to prevent the collision risk but do nothing to change the behavior that created the collision risk. The orbital fees not only don’t solve the problem but, by and large, they are asking the commercial sector to pay for the pollution that was created by legacy users who were largely governments.

While economic incentives can be an effective tool to affect behavior, it is important that there is a clear connection between the economic lever and the behavior that it seeks to influence.

The Earth is surrounded by human-made orbital debris in all shapes and sizes that includes everything from abandoned satellites and leftover rocket stages to the tiniest paint chips and droplets from spacecraft coolant systems.

The hazard is very much real. Given the ultra-fast speeds of objects in space (satellites in low-Earth orbit fly at 17,400 mph), even the most minuscule bit of rubbish could create havoc if it crashed into a functioning  spacecraft.

The question of how best to de-clutter outer space has produced a wealth of proposals: some whacky, whimsical or wanting of a sanity check. Many space junk clean-up ideas have already been proposed, including: catch-all space sweepers, fishing nets and harpoons, tethers, laser blasts, big and small space tugs.

One of the latest looks at the orbital debris quandary was completed by the Defense Advanced Research Projects Agency (DARPA).

Released with little fanfare a few months ago, it was dubbed "The Catcher’s Mitt Study" – to assess the debris problem and its future growth, determine where the greatest problem will be for U.S. assets and then, if appropriate, explore technically and economically feasible solutions for debris removal. [Worst Space Debris Events of All Time]

Operation: Catcher’s Mitt

The report explains that active debris removal was found to be required at some point to maintain an "acceptable level" of operational risk.

"Although projections show that it may take decades for the risk to become unbearable," there are several reasons to begin development of a solution today, the Catcher's Mitt study states.

A central finding of the study is that the development of debris removal solutions should concentrate on pre-emptive removal of large debris in both low-Earth orbit (LEO) a few hundred miles above the planet, as well as geosynchronous Earth orbit (GEO), the realm of communications satellites and other key spacecraft about 22,400 miles (36,000 kilometers) up.

More a warning than background to the vexing dilemma of orbital debris, the Catcher's Mitt study explains that "failure to address this problem has significant implications for the success of future space missions due to the potential increased number of on-orbit collisions with non-trackable, yet lethal, debris fragments."

Significant, but manageable

Although space debris is a growing concern and will have to be addressed at some point in the future, even in the most congested low-Earth orbit altitude regimes, the current risk from orbital debris is significant … but manageable, said Wade Pulliam, manager of Advanced Concepts of Logos Technologies in Arlington, Va., and the former program manager of DARPA’s Catcher's Mitt report.

"By significant I mean that it can be one of the top single contributors to the lifecycle risk of a satellite, but manageable in that the risk is still sufficiently low that it doesn't require a change in operations," Pulliam told SPACE.com. 

Pulliam noted that a recent study by The Aerospace Corporation projected the effects of the future debris environment over the next 30 years. It showed that for typical low-Earth orbit satellite constellations, the risk of space debris will add only 4 to 15 percent to the cost of the constellation, depending on the type of constellation.

"Of course, debris risk is statistical, so there may not be any problem at all or a collision will take out a satellite requiring a spare to be built and launched," Pulliam said. Still, a new significant debris event could statistically happen tomorrow which would greatly accelerate the growing risk and require a more immediate response, he cautioned.

Tragedy of the commons

In the big picture, Pulliam said that he considers orbital debris a human-made environmental problem.

"Although space is not an ecosystem per se, the problem is dependent on the cumulative effects of human activity over and above the ability of the nature system to balance like any other environmental challenge," Pulliam said.

Additionally, Pulliam advised that the constraints on finding an agreeable, cost-effective solution are remarkably similar to other current environmental issues. Specifically, the orbital debris problem can be characterized as a "tragedy of the commons."

The problem can also be explained by what is called "common but differentiated responsibility," which is also seen in other worldwide environmental challenges such as chlorofluorocarbons (CFCs) and global warming, Pulliam pointed out.

"It is likely new space-faring nations will make a similar argument if current mitigations efforts prove to be insufficient to forestall the deterioration of the low-Earth orbit environment and an international agreement on debris removal is required," Pulliam advised.

There is a "therefore" to Pulliam's view: That is, if you are one that believes that debris has become a risk which will soon make operations difficult in low-Earth orbit, then a top-priority has to be in continued research into cost-effective methods to remove debris mass already in orbit. That's because this mass is what will cause the future growth in the debris population. 

"There are many approaches that have been postulated for debris removal, but determining which are the most cost effective and demonstrating their utility is necessary to formulating a response to the overall problem with the lowest cost and risk," Pulliam said.

Up in the air

One lingering question that remains — putting think tank studies aside —is exactly who is in charge of orbital debris cleanup?

In the United States, the initial lead for Department of Defense (DoD) efforts regarding debris removal as called for in the new U.S. National Space Policy is reportedly the Office of the Secretary of Defense.

But still up for grabs (like space junk itself) is the delegation of the task to a particular organization within DoD. For example: the U.S. Air Force Research Laboratory; the Space and Missile Systems Center; or perhaps the Naval Research Laboratory.

"I think that the DARPA's Catcher's Mitt study clearly said that going after large, trackable, derelict debris is the most likely best recourse for debris cleanup," said Darren McKnight, technical director at Integrity Applications Incorporated in Chantilly, Va. "However, the best means to remove the large derelict objects is very much up in the air."

If history is any indication of the future, "the first large derelict debris removal action will most likely occur with a complicated, expensive rendezvous, grapple and move with a traditional propulsion system … though this approach will not scale well for the multiple objects that will likely have to be removed over the next few decades," McKnight told SPACE.com.

The price of delaying action

McKnight likens the orbital debris situation today to the observations of Nassim Taleb, author of "The Black Swan - The Impact of the Highly Improbable." The book describes the difficulty of dealing with highly improbable and highly unpredictable events that have severe repercussions.

Taleb accentuates the plight for those who try to prevent "Black Swans" because they are never appreciated if they are successful, since preventing something that was highly unlikely to begin with does not bring acclaim. Often, it is quite to the contrary; they actually get ridiculed for their attempts to prevent events that others have difficulty even imagining.

"I hope that we do not have such a situation with active debris removal actions. While the calculus of delaying action is much clearer, it will still require some vision from policymakers and technologists to act now to start real programs for active debris removal," McKnight said. "Nobody has won the Nobel Prize for preventing a disaster that never occurred."

• 

At 16:56 UTC on August 29, 2009, an Iridium communications satellite suddenly fell silent. In the hours that followed, the U.S. Space Surveillance Network reported that it was tracking two large clouds of debris—one from the Iridium and another from a defunct Russian military satellite called Cosmos 2251.

The debris was the result of a high-speed collision, the first time this is known to have happened between orbiting satellites. The impact created over 1,000 fragments greater than 10 centimeters in size and a much larger number of smaller pieces. This debris spread out around the planet in a deadly cloud.

Space debris is a pressing problem for Earth-orbiting spacecraft, and it could get significantly worse. When the density of space debris reaches a certain threshold, analysts predict that the fragmentation caused by collisions will trigger a runaway chain reaction that will fill the skies with ever increasing numbers of fragments. By some estimates that process could already be underway.

An obvious solution is to find a way to remove this debris. One option is to zap the larger pieces with a laser, vaporizing them in parts and causing the leftovers to deorbit. However, smaller pieces of debris cannot be dealt with in this way because they are difficult to locate and track.

Another option is send up a spacecraft capable of mopping up debris with a net or some other capture process. But these missions are severely limited by the amount of fuel they can carry.

Today, Lei Lan and pals from Tsinghua University in Beijing, China, propose a different solution. Their idea is to build an engine that converts space debris into propellant and so can maneuver itself almost indefinitely as it mops up the junk.

Their idea is simple in principle. At a high enough temperature, any element can be turned into a plasma of positive ions and electrons. This can be used as a propellant by accelerating it through an electric field.

The details are complex, however. In particular, the task of turning debris into a usable plasma is not entirely straightforward.

Lei and co focus their efforts on debris that is smaller than 10 centimeters in size, the stuff that laser ablation cannot tackle. Their idea is to capture the debris using a net and then transfer it to a ball mill. This is a rotating cylinder partially filled with abrasion-resistant balls that grind the debris into powder.

This powder is heated and fed into a system that separates positively charged ions from negatively charged electrons. The positive ions then pass into a powerful electric field that accelerates them to high energy, generating thrust as they are expelled as exhaust. The electrons are also expelled to keep the spacecraft electrically neutral.

Of course, the actual thrust this produces depends on the density of debris, the nature of the powder it produces, on the size of the positive ions, and so on. All this is hard to gauge.

And while the spacecraft does not need to carry propellant, it will need a source of power. Just where this will come from isn’t clear. Lei and co say that solar and nuclear power will suffice but do not address the serious concerns that any nuclear-powered spacecraft in Earth orbit will generate.

Nevertheless, the work provides food for thought. Space debris is an issue that looks likely to get significantly worse in the near future. It is an area where new ideas are desperately needed before the next big collision fills Earth’s orbits with even more debris.

(ed note: for more details, see: )

Ref: arxiv.org/abs/1511.07246 : Debris Engine: A Potential Thruster for Space Debris Removal

• 

     Faced with the challenge of capturing tumbling satellites to clear key orbits, ESA is considering turning to an ancient terrestrial technology: the harpoon.
     Used since the Stone Age, first to spear fish and later to catch whales, the humble harpoon is being looked at for snagging derelict space hardware.
     Decades of launches have left Earth surrounded by a halo of space junk: more than 17 000 trackable objects larger than a coffee cup, threatening working missions with catastrophic collision. Even a 1 cm nut could slam into a valuable satellite with the force of a hand grenade.
     The only way to control the debris cloud across crucial lower orbits — like those that allow observation satellites to go on monitoring our planet at the same local time of day — is to remove large items such as derelict satellites and rocket upper stages.
     These uncontrolled multitonne objects are time bombs: sooner or later they will be involved in a collision. That is, if they don’t explode earlier due to leftover fuel or partially charged batteries heated up by sunlight.
      The resulting debris clouds would make these vital orbits much more hazardous and expensive to use, and follow-on collisions may eventually trigger a chain reaction of break-ups.
     To avoid this outcome, ESA’s Clean Space initiative is working on the e.DeOrbit mission for flight in 2021. Its sophisticated sensors and autonomous control will identify and home in on a target — potentially of several tonnes and tumbling uncontrollably.
     Then comes the challenge of capturing and securing it. Several different solutions have been considered, including a throw-net, clamping mechanisms, robotic arms — and a tethered harpoon.
     The harpoon concept has already undergone initial investigations by Airbus Defence and Space in Stevenage, UK.
     Harpoons rely on three physical actions to ensure safe and clean grasping: a high-energy impact into the target, piercing the structure and then reeling it in.
     A prototype harpoon was shot into representative satellite material to assess its penetration, its strength as the target is pulled close and the generation of additional fragments that might threaten the e.DeOrbit satellite.

• 

• 

• 

A laser broom is a proposed ground-based laser beam-powered propulsion system whose purpose is to sweep space debris out of the path of other artificial satellites such as the International Space Station. It would heat one side of an object enough to change its orbit and make it hit the atmosphere sooner.

Technical description

Lasers are designed to target debris between one and ten centimeters in diameter. Collisions with such debris are commonly of such high velocity that considerable damage and numerous secondary fragments are the result. The laser broom is intended to be used at high enough power to penetrate through the atmosphere with enough remaining power to ablate material from the target. The ablating material imparts a small thrust that lowers its orbital perigee into the upper atmosphere, thereby increasing drag so that its remaining orbital life is short. The laser would operate in pulsed mode to avoid self-shielding of the target by the ablated plasma. The power levels of lasers in this concept are well below the power levels in concepts for more rapidly effective anti-satellite weapons.

NASA research in 2011 indicated that firing a laser beam at a piece of space junk could alter velocity by 0.04 inches (1.0 mm) per second. Persisting with these small velocity changes for a few hours per day could alter its course by 650 feet (200 m) per day. While not causing the junk to reenter, this could maneuver it to avoid a collision.

Other funded research into this area refutes NASA's claim and demonstrates the precise physics involved, which shows that space debris is re-entered regardless of the direction of laser illumination. Using a laser guide star and adaptive optics, a sufficiently large ground based laser (1 megajoule pulsed HF laser) can deorbit dozens of objects per day at reasonable cost. This work was summarized in an article in Wired Magazine.

• 

• 

• 

My series of posts have tried to wake up merchants and other spacers to the colorful travellers and phenomena of the space lanes. Mind the colorful people are usually pirates and barbarians and the phenomena you could usually do without. Sorry, those are the thought that come to me out of the ether. I just get custody of them, as George Carlin once said (I'd love to say I wrote this during a lightning storm with a bottle of Scotch in my hand but alas it's a sunny day and I'm sipping iced tea.)

Anyway besides your basic pirates there's another group out there to worry about. They are every bit as relentless (maybe more), they have better technology, they have excellent crews. The Polity Navy takes a dim view of them many times. I refer to the Patrol (with a nod to Lady Andre Norton of course).

There is no branch called the Patrol in most Polities but it's there. Politics indicates a Polity will field fleets to prevent invasion, and rebellion. These fleets will have the most powerful ships and weapons available as well as the highest technology level.

These fleets will be idle and trying to look busy 99% of the time. It's that other 1% that you keep them around for: war, blockades, rebellions, invasions, and spitting on the GHU-Emperor's statue. For fighting pirates these fleets are almost 100% useless. In building big ships to serve as deterrents you are concentrating your forces. Fighting a group of pirates or a smuggling fleet with a fleet like this is much like taking a sledgehammer to a swarm of gnats. The pirates go where the big ships aren't. Big ships require a scheduled route for political and defense considerations. This may be the same thing. Fleet Day may come early if your Planetary Baron is feeling uppity. Pray they leave early too.

• 

Add to this that a remote central government probably doesn't give a chinchilla's ass about your local concerns or the distress call of that lousy 200 ton free trader ... Roland, Siegfried? I forget the name.

After paying their share of taxes for the Polity fleet member worlds with any sort of leaderships will tighten their belts and pay another tax for their local fleet, usually referred to as the Patrol. Yes it is part of the Navy, much as some regard the Marines as part of the US Navy. You try telling a Marine that and I'll take pictures. Apart from a temporary alliance the Patrol and the Fleet do not work that closely. While the Fleet exists to protect the Polity, the Patrol takes care of things on a local level.

The frontier navy does not have the budget of the Fleet. Small ships are used with local technology that do not require special bases or technicians to maintain. Crew are small. There's no Marine equivalent, ship troops handle boarding actions. Ship's boats (30 dtons or average of 8.4 metric tons) are used extensively to augment firepower in a sort of mini-battlerider strategy. These ships are crucial in raiding pirate bases that traditionally have landing fields that are a nightmare for large ships.

The Patrol has relatively small ships (800 dtons {2,230 metric tons} and under and darned few 800 dton ships {warships are more like 300,000 metric tons}). They do try to be everywhere. They use technology locally available and are built for lengthy patrols. Finally the Patrol skipper has a high degree of autonomy. Beyond a few scheduled stopovers for various concerns a Patrol skipper has a group of star system they patrol in whatever fashion they choose, barring orders from above.

The autonomy part gives pirates the fits. The Fleet makes a show of arriving and leaving and goes for shock and awe. It's like a marching band. The Patrol shows up where and when you least expect it, much like the guy who steps on a subway train, starts playing a flute and passes the hat around.

There's a difference in culture as well. Navy officers (and crew where possible) will often be stationed in ships and fleets far from their homeworlds. Their first loyalties and interests are to the Polity, not some locals (barring shore leave.) The crew of the Patrol are the locals. The Fleet regards anti-piracy missions as search and destroy missions (usually against a base or a lone ship with phenomenally bad luck/judgement). The Patrol uses local contacts and local rumor mills to ferret out the informants and fences so necessary for successful pirate enterprises. There are even instances of one pirate ring informing on another group invading their territory to the Patrol. After all locals look out for each other.

The Parol is also relentless in mounting sting operations often using upgunned merchant ships or captured pirate vessels. These stings extend to Patrol crew operating undercover in starports to report suspicious goings on. Besides their own contacts and agents the Patrol cultivates good relations with the Scouts and the Free Traders. Both are valuable sources of information on local shipping. In the case of the traders some helpful tips might lead to the Patrol looking the other way when you have some duty free cargo in your hold.

The system is not perfect. For one thing in some areas the Patrol amounts to a private navy beholding only to its homeworld and little else. In Polities that are confederations local navies may be dominant. These look to their own world leaders and admiralty for orders first then the Polity. The central government usually takes a dim view of this and restricts ship size and armament when it can.

Even so Patrols are often scenes of power struggles as local commanders do not always cooperate with others in a cluster funded navy. It gets worse if one or more worlds rebels against the Polity. In the case of a rebellion the Patrol is usually the first to get the ax. The Polity Fleet will regard them as possibly disloyal and move to disarm them and intern their ships. Similarly some local planets may regard them as tainted by offworld contacts and interests and move to eliminate their officers at the very least.

In a final  sign that the Universe's most fundamental force is irony: many Patrol ships faced with their homeworld turning rebel, turn pirate.

• 

• 

      All traders know there will come a time when you are hailed, intercepted and boarded and you'd damned well better make the right decisions or risk getting your freighter shot to pieces, see your crew get shot to pieces and lose everything.

     The enemy has the weapons, has the troops, and the skill. They are the Patrol!

     Consider.

     The Fleet is the creation of a number of advanced and populated worlds. It exists to preserve the status quo, the fat freighter plying their way between major centers of commerce. They have the tax base to let them by the big ships, pay their crews the premium salaries and get the best and brightest. Any pirates operating in the core worlds better have a masterful plan, make their score and then go into cold sleep for a few hundred years.

     Out on the Frontier ... there is still commerce and trade (much of it legal). There are also pirates as always. The Frontier has the Patrol, armed well enough to raise merry Hell with one or more pirate ships. It's a smaller, leaner operation and it is chronically underfunded. The worlds that support it have less money, less of s pool of skilled crew. They need as many ships as possible to cover as many hot spots as possible. How do they pay for this?

     Asset forfeiture!

     The business model is simplicity itself. Most traders smuggle at least part of the time. Nearly everyone's smuggled at least once. Make a trader pull over and you have a decent chance of finding some swag. What then? The Patrol does not maintain extensive correctional facilities and most planetary governments don't want the refuse of space crowding out their native felons. The easiest ways to punish for nonviolent crimes is fining, suspending licenses, and exile.

     Under fines read confiscating your cargo (all of it) and maybe your ship for a serious enough smuggling offense. Knowing what goods are contraband or may be regarded as such on your port of cal is a big job. It's where your deckmasters pay for themselves several times over.

     For a big enough offense the entire ship may be forfeit. This rarely happens because one case of this can scare the free traders away for years. It is a great tool for starting up your own shipping line and keeping outsiders from competing with you. But then your trade efforts might still be hampered for some time. Other free traders may not want to support an organization that started out screwing their own.

     The Banks have a handy solution to the immense power of asset forfeiture the Patrol wields. In the case of a mortgaged ship being seized, only part of that ship belongs to the offending party. The rest belongs to the Bank and in such cases the Patrol gladly hands over the ship in exchange for a fraction of the principal already paid to the Bank. The Bank gets a ship back that it can mortgage again, the Patrol gets a fat check, and evildoers are punished. Sometimes Banks even let these ships go cheap since they are often used. there might be problems with former owners seeking to steal the ship for various reasons (hidden compartments, vital information encoded on the computer etc.)

     Please note in many cases the Bank turns right around and remortgages the ship to the same poor slob that it was confiscated from. Hey, crews don't grow on trees, every day that ship is sitting in a port it could be earning money for the shareholders. Besides, the so called lawbreakers already passed a background check once! So they broke a local law! It happens.

     Note that the Patrol could sell these confiscated ships and pay the rest of the principle in the mortgage, but seldom has the interest or networking to get a good price. Also the Banks pay taxes and wield a lot of clout in many local governments. You don't want to tick them off.

     Less extreme than asset forfeiture is the phenomenon of spot inspections. A bunch of Patrol inspectors boards you and finds your vessel to be a flying deathtrap. Stiff fines ensue! Or someone 'notes/ a leak of a vital commodity (fuel, propellant, air) just as it is vented explosively (did someone nudge a switch?). What a pity. The nice Patrol Captain is willing to sell your some more fuel or whatever at triple cost.

     All these dirty trick can be done by space port inspectors. They aren't done commonly because the Patrol usually gets to traders first and getting gouged by a Patrol ship is avoidable in theory, if they can't intercept. The way you avoid gouging on planet is avoiding that planet. Not good for business.

• 

(ed note: This happens in an episode of The Expanse entitled "Rock Bottom." The gutter punk Diogo assists his bitter, cranky Uncle Mateo, a working-class 'rockhopper' who explores asteroids looking for precious ore in the rustbucket spaceship Xinglong.

They are intercepted by the MCRN Scipio Africanus, a Martian border patrol vessel. Mateo is busted for an expired transponder and ordered to impound his haul. This will leave Mateo bankrupt.

After the Scipio Africanus starts to leave, an enraged Mateo kicks his nephew off the Xinglong in an space suit, then goes on a suicide run on the Martian ship. Mateo uses his ship to hurl a deadly cloud of high velocity asteroid shrapnel at the Scipio Africanus, as an impromptu kinetic energy weapon. This kicks the war into high gear.)

• 

      But the function of the Monitor Corps, the law enforcement and executive arm of the Galactic Federation whose sixty-odd intelligent species were represented on the staff of Sector General, was something that needed clarification, I thought. The result was a very long novelette of some 21,000 words.

     Essentially the Monitor Corps was a police force on an interstellar scale, but I did not want them to be the usual ruthless, routine-indoctrinated, basically stupid organization that is so handy to have around when an idealistic principal character needs a bit of ethical conflict. Conway was one of the good guys and I wanted them to be good guys too, but with different ideas as to the kind of activity that produces the greater good.

     Their duties included interstellar survey and first-contact work as well as maintaining the Federation’s peace—a job that could, if they were unable to discourage the warmongers, give rise to a police action that was indistinguishable from an act of war. But the Corps much preferred to wage psychological warfare aimed at discouraging planetary and interplanetary violence and when, despite their efforts, a war broke out, then they very closely monitored the beings who were waging it.

     These warlike entities belonged to a psychological rather than physiological classification, and regardless of species they were the classification responsible for most of the trouble within the Federation. The story told of the efforts of the Monitor Corps first to attempt to prevent the war and then damp down the war, and Conway and Sector General came into it only when things went catastrophically wrong and large numbers of human and e-t casualties had to be dealt with. The original title of the story was “Classification: Warrior.” (later changed to Occupation: Warrior)

     Normally I do not like stories of violence or the senseless killing that is war. But if a story is to hold the interest of the reader there must be conflict, which means violence or struggle of some kind. However, in a medical SF story of the Sector General type the violence is usually the direct or indirect result of a natural catastrophe, a disaster in space or an epidemic of some kind. And if there is a war situation of the kind that occurred in Star Surgeon, then the medics are fighting only to save lives, and the Monitor Corps, like the good little policemen they are, are fighting to stop the war rather than win it—which is the essential difference between maintaining the peace and waging a war.

• 

      EARTH as such did not have a space navy; there was no danger of attack from space and, as far as Earth was concerned, the outplanets could take care of themselves. Nor did either WestHem or EastHem; with their ICBM's they did not need or want any subspace-going battleships. Nor did any of the planets. Newmars and Galmetia were heavily armed, but their armament was strictly defensive.

     Thus InStell (the Interstellar Corporation) had been forced, over the years, to develop a navy of its own, to protect its far-flung network of merchant traffic lines against piracy; which had of course moved into space along with the richly-laden merchantmen. As traffic increased, piracy increased; so protection had to increase, too. Thus, over the years and gradually, there came about a very peculiar situation:

     The only real navy in all the reaches of explored space—the only law-enforcement agency of all that space—was a private police force not responsible to any government!

     It hunted down and destroyed pirate ships in space. It sought out and destroyed pirate bases. Since no planetary court had jurisdiction, InStell set up a space-court, in which such few marauders as were captured alive were tried, convicted, and sentenced to death. For over a century there had been bitter criticism of these "highhanded tactics," particularly on Earth. However, InStell didn't like it, either—it was expensive. Wherefore, for the same hundred years or so, InStell had been trying to get rid of it; but no planet—particularly Earth—or no Planetary League or whatever—would take it over. Everybody wanted to run it, but nobody would pick up the tab. So InStell kept on being the only Law in space.

     This navy was small, numbering only a hundred capital ships; but each of those ships was an up-to-the-minute and terribly efficient engine of destruction, bristling with the most modern, most powerful weapons known to man.

• 

This leaves the question of what sort of vessel would be used as a light patrol craft in orbital space.  This might be best described as a cutter or a patrol boat, and would be intended for use in a friendly orbit with nearby basing facilities.  Each watch would have a crew of at least three — officer, sensors/weapons, and helm, though the number might rise higher for workload reasons.  Particularly if there are a significant number of vessels to monitor, multiple sensor operators might be required.  After 6 hours on watch, efficiency drops dramatically, so while a short-endurance vessel might get away with one shift and a microwave, a vessel designed for anything more than that will need multiple watches, some facilities for off-duty crew, and probably a mechanic or two.  (In most circumstances it would make more sense to place all of this on a customs base of some sort instead of on the cutter itself.)

Because the cutter will be called upon to perform boarding missions, the crew might well be outnumbered by the Espatiers detachment.  Weapons fit would be limited, probably to a medium laser for takedowns, and maybe an EMP generator (assuming such a weapon is practical).  Heavy kinetics are unlikely to be seen on patrol craft for reasons mentioned in Section 6, although surface-effect and precise unitary ones are potentially useful.  The drive is most likely to be nuclear-thermal, though chemfuel is possible, particularly for smaller craft.

At the low end of the boarding-craft spectrum, we have a one-shift vessel with a crew of three, incapable of true independent operation.  It’s dispatched to hunt down a specific target and deliver a squad or two of Espatiers.

At the high end is a vessel ("large cutter") that has a crew of a two dozen, can operate independently for a month or more, carries a full platoon of Espatiers, and can serve as a light warship if necessary.  A vessel of this size might carry a small, probably unarmed parasite intended to transport a squad of Espatiers over to a potentially hostile vessel.  It has been suggested that this sort of vessel might have a modular troop/weapons bay, allowing it to serve as a corvette as well as a cutter.  The biggest limit on its endurance is the lack of a spin hab, which would adversely affect the health of the onboard Espatiers.

---

All of this leads to the question of patrol outside one’s own orbital space.  The scenario in question is one that resembles more than anything else is that of the various naval detachments of the 19^th century, such as the Asiatic Squadron and the China Station.  The objective is to protect the power’s interests, and those of their nationals engaged in commerce, in a relatively wild part of space.

---

• 

• 

Several people have suggested some form of “patrol carrier” or “space control ship”, as discussed in Section 1.  This would involve a single large ship with several parasites, and possibly significant weapons of its own.

The parasites would be responsible for a number of missions, and would likely be a modular system.  At the largest end are the drives which serve as the basis for manned missions.  Option probably include general shuttle (passengers and light cargo), boarding shuttle (espatiers and maybe a few weapons), gunboat/scout (light weapons) and heavy lancers (used to threaten someone into seeing things your way).  Smaller drives would be used for recon, light lancer, and other uses.  The exact numbers and capabilities of each are dependent on both technical and operational details outside the scope of this paper.

It has also been suggested that modularity could be extended to the patrol carrier itself.  The parasite bays could be swapped out for supplies, quarters, or even additional weapons as needed for the mission.

The drawback to the concept is that the owing power’s entire presence in the area is dependent on a single ship.  If the patrol carrier is damaged or destroyed, the parasites will likely be sitting ducks for an enemy.  On the other hand, the same could largely be said of US aircraft carriers today.

The patrol cruiser carrier is more likely to be used in large areas, such as a planetary moon system, where there are multiple powers and multiple potential issues simultaneously.

---

If the objective is to keep an eye on one specific power, it makes as much sense to simply keep a single “frigate” on station.  This frigate would resemble the large cutter described above, but with more weapons and the capability to support its crew for months at a time.

---

• 

Another alternative for presence missions is to keep most of one’s forces centralized, ready to react to situations.  Some small presence ships would probably remain on station to handle minor issues, while centralization would theoretically allow savings in forces.  The biggest potential issue is the possibility that the smaller ships will be unable to handle problems that could be stopped by the bigger forces.  This also suffers from the problems mentioned below involving variable transit time.

One potential issue that this type of ship (or any ship on a distant station) suffers from is the fact that it is several weeks to several months away from help.  This means that if any problem develops, it will have to deal with it out of its own resources.  The obvious comparison is to the age of sail, but that analogy falls apart when one considers that communication lags will be hours long at most.  Not only that, travel times will vary significantly with orbital positions.  Anyone trying to make trouble, particularly someone planning a rebellion, would take that into consideration.  At the same time, their opponents would be able to see the same thing, and would probably step up security at times when help is furthest away.

Another issue for distant stations is supply and operations.  The problem is quite simply that even with high-Plausible Mid-Future (high-PMF) drive tech, shipping in all of the supplies required is incredibly expensive, and the operational issues are even worse.  Typical wet Navy cruises are six months or so (including port visits.  SSBNs, which are probably the best analogy for long-duration spacecraft, only stay out for 90 days) and transit time will be at least a month.  This in turn means that it will probably take at least 4 ships for every one that is forward-deployed.  The obvious solution to this is to home-base the ships at the area to be patrolled.  This in turn requires a local ally, making it only useful in balkanized territories.  Even the use of a semi-neutral power for supply is a dubious proposition.  They could be pressured to cut off your supplies, or someone could slip a nuclear weapon aboard a supply shuttle.

It has been suggested that pre-positioned fleets could be used as forward defense against a potential enemy invasion.  This falls afoul of three issues.  First, as described above, the supply problems are likely to be horrendous.  Any power that is strong enough to pose a potential invasion threat is likely to dominate the area to the extent that a friendly supply base is not available.  Second, said enemy will be able to easily overwhelm your forward-deployed forces (see the 4 to 1 ratio described above).  Thirdly, the legal issues with deploying forces in their Hill Sphere are likely to be significant.  It would be a far better plan to use InterPlanetary Ballistic Missiles (IPBMs) to wear them down as their fleet approached, and concentrate your forces to defeat whatever arrives.  The fact that the operational costs of the deployment are not incurred would also allow the purchase of more vessels, and a better force ratio at home.

---

Another suggestion for military patrols is the use of cyclers.  A cycler is a large space station launched into a specific orbit so that it passes by two planets repeatedly and at predictable intervals.   Due to orbital mechanics, they generally make a quick passage in one direction, and a slow one in the other.  The idea behind cyclers is that they avoid accelerating and decelerating lots of equipment that is used on every trip, such as life support and passenger quarters.  The cycler itself provides no aid in accelerating and decelerating the passengers/cargo during transfers.  The problem is that this only makes sense when delta-V is very expensive.  The low duty cycle of the cycler is a significant problem, as is the need for perfect rendezvous with it.  In most PMF settings, nuclear-electric drives would render them obsolete.

For military use, the cycler is even worse.  To quote Milo: “So wait, are you postulating large, poorly mobile weapons platforms that fly past planets on predictable courses at high speeds?”  The actual concept proposed was to use the cycler more as a base than as the weapon platform itself, but a number of issues remain.  The cycler is vulnerable in the extreme to kinetics, even unguided ones, and it has a very low ‘duty cycle’ with respect to its target, which means either extremely high costs, low visit rates, or weak patrols.  It also greatly simplifies the task of anyone planning mischief.  They know exactly when the patrol will arrive and how long it will stay.  It has been suggested that the cycler could take care of some of the housekeeping issues for the carried warships, but this is impractical in operation.  The ships would be unable to fight over long periods, and would have to leave when the cycler did, or be forced to stay until the next pass.

---

An alternative to cyclers is some form of ‘Mobile Base.’  This is quite similar to the proposed cycler, but instead of swinging by every few years, it moves to the area of interest and stays until the problem is solved.  This base carries extra remass, supplies, ammo, repair equipment, and probably R&R facilities for the crews.  It can afford to use lower-powered engines and less delta-V than a conventional warship, as it is only intended to deploy for serious crises which will occur over prolonged periods.  The combat vessels would arrive early and stay on station until the base got there, and then use it to remain operational.

• 

• 

It was true that officers were not supposed to leave a ship while under way, but notwithstanding the regulations, Beckley saw no good reason for making them forego their daily exercise. The Pollux was swinging lazily in a wide orbit about the Jovian System, her electronic blasts cold and dark, patrolling for routine traffic-control purposes. Forbidding men to go over the side was as senseless a restriction as to prohibit swimming from an anchored ship.

He made his way to the boat deck, and as he stepped out of the air lock onto the broad fin he was impressed by the size of the huge vessel. Its hull sloped upward and away from him, gray in the dim light of a dwindled sun, and he saw for the first time the row of alcoves let into the ship’s side that sheltered the boats. Those, he knew, were used for the reconnaissance of asteroids or areas too rugged to put the ship down on, or for minor searches, or for rescue expeditions. Star-class cruisers, being designed for all-planet service, were equipped with vertical and horizontal fins to stabilize them when easing into an atmosphere, and the horizontal ones made ideal landing decks for their boats.

---

It fell to Fraser’s lot to conduct the Abandon Ship Drill. The Polliwogs were tense as televox repeaters throughout the ship chanted the call to the boats. Number 3, on the starboard side, was a balky sl*t. Five times out of six her tube would not fire unless preheated with a blowtorch. It was a mystery why, for they had successively put in four spares and still Number 3 performed in the same erratic manner. But today she took off like a startled dove at the first touch of the coxswain’s button. Pure luck that was, for there was not a chance to use the torch with watchful umpires writing down all they saw.

The Castor Beans pawed through the returned boats, looking for error, but their search was unsuccessful. Boat boxes were correct, down to the first aid kit, as was the power installation and the handling. Fraser drew another four-o and was excused.

Payload
Crew	25
Hab Module	100 tons
Consumables	25 tons
Other Payload	75 tons
Total Payload	200 tons
Propulsion Bus
Engine+Radiator	200 tons
Tankages+Keel	100 tons
Stats
Dry Mass	475 tons
Loaded Mass	500 tons
Propellant Mass	500 tons
Wet Mass	1000 tons

The discussion thread about 'Industrial Scale of Space' veered, among other things, into a discussion of patrol missions in space. My first reaction was that (so long as you aren't dealing with an interstellar setting) there is no place in space for wartime patrol missions. But the matter might be more complicated, and for story purposes probably should be.

According to The Free Dictionary, patrol is The act of moving about an area especially by an authorized and trained person or group, for purposes of observation, inspection, or security. This fits my own sense of the word, and is in fact a bit broader, 'security' including SSBN patrols, which are not observing or inspecting anything, just waiting for a launch order if it comes.

In a reductionist way you could say that all military spacecraft are on patrol, since they are all on orbit, and if they are orbiting a planet they have a very regular 'patrol area.' But this is not what most of us have in mind. We picture a patrol making a sweep through an area, looking for anything unusual, ready to engage any enemy they encounter, or report it and shadow it if they cannot engage it.

Back in the rocketpunk era it was plausible that, say, Earth might send a patrol past Ceres to see if the Martians had established a secret base there. But (alas!) telescopes 'patrolling' from Earth orbit can easily observe the large scale logistics traffic involved in establishing a base; watch it depart Mars and track it to Ceres. If you want a closer look you can send a robotic spy probe. If you engage in 'reconnaissance in force' by attacking Ceres, that is a task force, not a patrol.

In an all out interplanetary war there may be plenty of uncertainty on both sides, but very little of it can be resolved by sending out patrols.

---

But of course all-out war is not the context in which the Space Patrol became familiar. I associate it with Heinlein's Patrol; apparently the 1950s TV series had an independent origin (unlike Tom Corbett, who was Heinlein's unacknowledged literary child).

The rocketpunk-era Patrol, which in turn gave us Starfleet, was placed in the distinctly midcentury future setting of a Federation. This is as zeerust as monorails. But plausible patrolling is not confined to Federation settings. It can justified in practically any situation but all out war.

Orbital patrol in Earth orbital space will surely be the first space patrol, and could be imagined in this century. It might initially be a general emergency response force, because travel times in Earth orbital space are short enough for classical rescue missions. On the interplanetary scale, with travel times of weeks or more likely months, rescue is rarely possible. But eventually power players will want some kind of police presence or flag showing in deep space.

As so often in these discussions, I picture a complex and ambiguous environment in which policing, diplomacy, and sometimes low level conflict blur together. To take again our Earth-Mars-Ceres example, there are kinds of reconnaissance that cannot be carried out by robots (short of high level AIs). If Ceres closes its airlocks to liberty parties from a visiting Earth patrol ship, that conveys some important intelligence information.

---

The ships that perform these missions will be fairly large (and expensive). They must carry a hab pod providing prolonged life support for a significant crew: at least a commander and staff, SWAT team of espatiers, and some support for both.

Let us say a crew of 25—which is cutting the human presence very fine. Now we can venture a mass estimate. Allow 100 tons for the hab compartment plus 25 tons for crew and stores plus 75 tons other payload, for a total payload of 200 tons. Let the drive bus be 200 tons for the drive, including radiators, and 100 tons for tankage, keel, and sundry equipment.

Our patrol ship with a crew of 25 thus has a dry mass of 475 tons, mass fully equipped 500 tons, plus 500 tons propellant for a full load departure mass of 1000 tons. Cost by my usual general rule is equivalent to $500 million, perhaps $1 billion after milspecking, expensive compared to military planes, cheaper than major naval combatants.

This is no small ship. If the propellant is liquid hydrogen the tanks have a volume of about 7000 cubic meters, equivalent to a 7000 ton submarine. The payload section is about two thirds the mass of the ISS and of roughly comparable size, though the hab is probably spun giving the prolonged missions.

Armament is necessarily modest. The 75 tons of additional payload allowance probably must include a ferry craft for the espatiers and an escort gunship or two, plus their service pod, leaving perhaps 15-20 tons each for kinetics and a laser installation. The laser might be good for 20 megawatts beam power, with plug power from the 200 megawatt drive engine.

This ship is no laser star, but the laser is respectable. Assuming a modest 5 meter main mirror and a near IR wavelength of 1000 nanometers, at a range of 1000 km it can burn through Super Nano Carbon Stuff at rather more than 1 centimeter of per second. Its armament is also rather 'balanced.' My model shows that this laser can just defeat a wave of about 1000 target seekers, each with a mass of 20 kg, closing at 10 km/s—thus a total mass of 20 tons, comparable to its kinetics payload allowance.

Deploying troops, or personnel in general, is impressively expensive: About three fourths of the payload and cost of a billion dollar ship goes to support and equip a crew of 25, with perhaps a dozen espatiers. For comparison the USS Makin Island (LHD-8) displaces 41,000 tons full load, carries a crew of 1200 plus 1700 Marines, and costs about $1.8. So by my model it costs about as much to deploy one espatier as 80 marines.

And this ship is about the minimum patrol package, so standing interplanetary patrol is a costly and somewhat granular business, something not everyone can afford.

---

SELECTED COMMENTS

TONY: I was maybe a little bit hasty earlier in saying that patrolling was of no value. It does have the value of giving you immediate reaction capability in a crisis. And in an environment where transit times are weeks or months, that can be important. IOW, while there may well be no physical horizon to patrol beyond, there is a time horizon.

However…a patrol vessel for that purpose could not be a relatively fragile assemblage of modules and cargo. This ship is going to have to fight it out with whoever else has a patrol vessel on-station — as well as any local forces that might exist — then dominate the local space until reinforcements arrive. So it's either got to be analogous to a pre-WWI overseas station cruiser, or the operator has to accept abandoning the hab and interplanetary drive (perhaps permanently) in order for the rest to be able to fire and maneuver effectively.

FERRELL: I don't think that "space patrols" would be like navy, or even air force patrols. It would be more like a giant figure-8 in the sky. Only with weapons and spy-gear...I do think that the 'patrol ship' would have extensive spin-hab and payload sections, but I think that the weapons mounted on the ship would be mostly point-defence, while the ship would also carry drones that mount the offensive weapopns (missiles and/or lasers)and be controlled from the ship. I also think that 'partols' would be more like convoy escorts (or raiders), 'show-the-flag' type, area security (like orbit), but I don't think you're going to send a billion dollar spacecraft from orbit 'A' to orbit 'B' and back again, just on the off chance that they would run into an enemy 'craft. It would be more like the bomber-interceptor type of combat. Deverting a 'show-the-flag' patrol to a hot-spot would be the exception rather than the norm. The only reasons I can see that you'd have these ships on a 'patrol' like Rick has discribed, is to keep close to convoys, unfriendly folk, or as mobile intelligence-gathering platforms. The customs/law-enforcement/anti-piracy/counter-terrorisim mission for your espatiers would be secondary. I further think that 'patrol ships' could be more like a mobile space station that are sent to orbit a planet or moon for short amount of time, and then off to the next target.

So...'space patrols' aren't going to be like 18th century sailing navy patrols, or even modern-day SSBN patrols. If you could send railroads on combat patrols, 'space patrols' would be like that...

ELUKKA: Shameless plug: I happened to design a paramilitary patrol/interceptor ship recently. Well, not really a coincidence as it was inspired by a previous discussion here. It'll manage an interplanetary flight but I imagine it's made more for smaller operational areas, say a gas giant's moon system.

Open-cycle gas core NTR engines, thrust around 1 g (or nearly 3 with LOX injection at the cost of some isp), delta-v 30 km/s. Propellant is methane. There's a secondary chemical engine for operation near other craft as the main engines do have radioactive exhaust.

It has a fairly big 140 tonne hab module and a turreted laser. Total mass is about 2,200 tonnes. Besides going with a high-thrust engine, I find it surprisingly similar to the craft Rick described!
The hab's got a wraparound radiator and the engines get rid of the brunt of their waste heat by the way they work (open-cycle cooling) but… no, they're probably still not enough. I did a terrible thing and sorta threw on radiators that I thought looked good instead of running the numbers. :P
(I did mathify the rest of the design though)

click for larger image

click for larger image

ELUKKA PATROL SHIP

Engine	Open-cycle GCNR
Docking Engine	Chemical (LOX-methane?)
Propellant	methane
ΔV (High-Gear)	30,000 m/s
Wet Thrust (High-Gear)	1g
ΔV (High-Gear)	30,000 m/s
Wet Thrust (Low-Gear)	6g
ΔV (Low-Gear)	? m/s
Habitat Module	140,000 kg
Weapons	x2 laser turret
Wet Mass	2,200,000 kg

FERRELL: Elukka:, your ship is great! As an interceptor or convoy escort, it looks like a good compromise between cost and mission demands. I could see it being used very handlly as a customs inforcer or as an asteroid deflector, as well as other missions. As a secondary armed spacecraft, this is what I imagined a "real" space fighter would be like. Your ship would be perfect for an independent colony or minor power.

Ferrell

CLAY:
     We already have space patrols, and we call them spy-sats.
     I just don't see this scenario. The cost, the mass, the vulnerability of a single mirror as our primary means of offense and defense.
     So your laser can burn 1000 incoming big projectiles? Big deal. This has always struck me as the major flaw in single laser configurations—the assumption that the enemy won't just buckshot you to death.
     Imagine this patrol ship up against robot ships using auto-canon to blast out clouds of shrapnel heading your way from beyond your laser's range and riding into your projected path of travel.
     Sure, they miss a lot, but they have hundreds of thousands of projectiles zipping towards you too. How do you track a cloud? How do you blast it? Can you paint that much space with your laser before overheating? (the answer is that is debatable, the classic Purple/Green debate)
     All it takes is for the shrapnel to rip apart your mirror, or radiators, or sensors, or whatever.
     And then boom...
     Here comes the slow nuke to turn your patrol ship into a flash of light that no longer exists.
     More realistic are lots of robot patrols—cheap and expendable. They swarm. They spy. They report. And eventually they fail and self-destruct. No muss. No fuss.
     Plus they're cheap and easy. NASA could build these today if it wanted.
     Sorry. I just don't see this scenario as very plausible.

     Hey—I just had a weird idea for these drone ships.
     Do you think it would be possible to design them to cannibalize themselves for ammunition?
     In other words, they'd lock onto a target, fire their basic store of ammunition, and if the target wasn't destroyed, the drones would be built in such a way that they could begin consuming their parts for ammo until the drone was nothing but the basic power unit, firing computer, attitude determination and control system (ADCS), and the rail gun.
     Everything else. The shell. Primary thrusters. Etc… Fired down range. I wonder how much you could scavenge if you had no intention of bringing it home again. (This is done in the simulation game High Frontier, except more so. The ships have Santa Claus machines that can canabalize unused equipment and manufacture needed equipment)

(Somebody suggested to Clay that patrol ships would be for inspection, not main-line combat work. Therefore it wouldn't matter that patrol ships were vulnerable to a sky full of buckshot)

CLAY:
     Well, these patrol ships are obviously meant for combat to some extent if we are arming them. My argument is that arming them, and indeed sending them, is pointless.
     Patrol ships can't outfight the drones cost effectively, nor can they out-patrol the drones either from a cost-effective standpoint.
     And I've read the arguments regarding space battle here and elsewhere, but I think they bear repeating in this context.
     There just isn't a scenario where dispatching isolated patrol ships with limited weaponry for long-range reconnaissance makes any sense unless you are actively trying to get attacked in order to justify going to war (a la American PT boats harassing Japanese warships pre Pearl Harbor)

BYRON:
     My overall view on this is that any sort of presence patrol will be in the form of a station, not individual ships. It's far cheaper in remass, and you get more ship for your money, as you don't need deep-space endurance. There might be a few ships for flag-showing patrols, but those would be very rare.

     Tony, Yes, but there are two major problems with that. First, the fact that you spend as much time coming back as you did going out. Second, the fact that you are only "on station" for 1% of the time. Yes, you can stop at the target, but the mass penalties for that sort of thing are rather severe.

     Elukka: The ship looks impressive. Do you have any more numbers?

     Clay, a single big laser will tend to be more powerful than several small ones. It has a longer effective range, and thus starts burning things sooner. I do agree that a few defense lasers would be helpful, but the main offensive laser will likely be a single unit.
As for attacking lasers, I'm in favor of sand clouds.
The point of armament is to provide the ship with some sort of chance against an enemy. If they can't outfight drones (which I won't take as a given) they still will do better with guns than without guns.

     If anyone's interested in ship design, I've recently made a spreadsheet that automates a lot of it. It was originally for Rocketverse but it's pretty adaptable. If you want a copy, I'll find a way to get it to you. I also have a Newtonian space battle tracker that works with it.

CAMBIAS:
     I think patrolling in space is a waste of time. You're wasting energy and reaction mass putting your ship in one particular orbit — thereby pretty much guaranteeing no enemy will be encountered in that orbit.
     The life-support cost is tremendous — not just in launched mass but also radiation exposure and the "opportunity cost" of having those crewmen on a trajectory to point A rather than any other point. Given the capabilities of modern drones I can't imagine any spacefaring power which would send out humans to snoop around potential threats.
     Instead of a patrol ship, I'd envision something like a frontier fort — a base from which missions can be launched, with telescopes to monitor that whole part of the Solar System, hardened defenses, long-term self-sufficiency, etc.
     One can imagine "forts" like that in key locations around the system — Saturn orbit, possibly the Jovian trojans, etc.

BYRON:
     The only reason to send manned ships is for "courtesy visits" and that's a pretty flimsy excuse. If your intel people are reasonably competent, they'll have agents aboard cargo ships going there. I somewhat agree with the "fort" theory, but I'd go farther and make it a full base, with facilities for crew and family, moderate repairs, etc.

THUCYDIDES:
     Patrolling will reduce the time horizon for the force which engages in it, which is really the point, I think.

Arguments that the patrol vessel is vulnerable are somewhat moot, since if the vessel is attacked, then it is an unambiguous signal that hostilities have commenced (unless the owning Power is willing to tolerate the loss for political or military reasons of their own).

     I would argue that a patrol vessel on the lines Rick has described would be a two part vessel. The Hab would be an independent space vehicle in its own right, while the major portion of the ship (keel, engines, radiator main assembly, Liniac and mirror) are also an independent vessel. Once the decision is made to land a shore party (or liberty party for that matter), the hab undocks and trundles off while the weapons platform remains in the High Guard position (Overwatch position higher in the gravity well).
     For Elukka, who seems to have a flare for this sort of thing, the main platform would look somewhat like a paper airplane, with large triangular radiators along the truss. The engine is at the wide end (radiators corresponding to where most of the heat generation is) (engine might be at the pointy end if it emits radiation) and the mirror is in the nose, perhaps in a "thimble" turret at this scale. Tankage, KKV's etc. are in the spaces between the "wings", and the hab is hanging off one of the hard points. Depending on the scale (and given the description), the hab might resemble a pair of spare tires hanging from a medium length girder bridge (counter rotating so they do not impart momentum to the carrier vessel). If you really want to take the "paper airplane" analogy seriously, then there are three fins and most of the other hardware is attached to the truss on the "top" of the paper airplane.

     The big advantage of this design is the carrier need not go with a manned hab, and indeed the hab could be the control station for a constellation of these vehicles, making it adaptable for everything from patrolling to being the nucleus of a constellation or task force.

BYRON:
It wouldn't reduce the time horizon by enough to matter in most cases. Not if the opponent was smart. If you're basically going there, swinging through the system, and leaving, the time in the system is going to be minimal compared to transit time. It's like sending "patrols" to, say, Deigo Garcia from the US by steaming a ship all the way around the world, and not stopping there, just sailing close by once, and leaving. Oh, and the ship can't turn around once it's past. Response time might be less if you have two, but no matter what, they'll wait until you've passed to make trouble.
If you choose to stop in orbit, that's slightly different, but unless you only want occasional visits, it makes a lot more sense to build a permanent base. You only have to ship supplies, and your crews will be a lot happier. Plus, the ships you have won't have to carry stuff like spin habs, as the missions aren't that long.

TONY:
     I think some people are not understanding what a patrol is in the context of near and medium term interplanetary spaceflight. The bojective will not be to go there and come back, or go to several places and pass through each without stopping. The objective will be to go and stay for the suration of the mission (months or years), so that if anything happens somebody will be on-hand to handle it. The patrol area is not a large volume of space. It's the tactically relevant volume of space around a point of interest, like a planet or an asteroid. So yes, there are some affinities with the fortress analogy and the spy sat analogy, but only some.
The patrol ship needs to do three things:

1. Go to the patrol area
2. Remain on station
3. Fight if and when the time comes to fight

     Notice that these three requirements would best be met by three different spacecraft. But since we don't have three different spacecraft, we'll make do with three different modules:

1. Interplanetary propulsion
2. Habitation
3. Combat

     The interplanetary module takes the hab and the combat modules to the patrol area. The hab is lived in and the combat module manned while on patrol station. If shooting starts, the combat module detaches from the hab and goes to work.

     Note that the combat module need not be monolithic. It could be augemtned by orbital or even self propelled sensor and weapon platforms. The reason for its existence — and the existence of the whole patrol ship complex — is to place humans in the loop in tactical time. It doesn't exist to be a tripwire, or to be here one day but gone the next. It exists to be available to fight and to actually fight when called on to do so.

MILO:
     I'll note that I am only against deep space patrols. Ships in orbit around an enemy planet (or a partially enemy planet, such as a multi-faction world or a friendly world that's under invasion, or a potentially enemy planet, that you suspect but aren't sure is planning something nefarious) can reasonably make use of some patrol tropes, although it's not quite the same.
     One issue with "patrolling" this close to an enemy planet, without access to stealth, is that the enemy is unlikely to let you unless you show up in enough force to strongarm their defenses. If relations are merely strained rather than actively hostile, though, then a show-the-flag mission is viable.

Tony: "I was maybe a little bit hasty earlier in saying that patrolling was of no value. It does have the value of giving you immediate reaction capability in a crisis."

     Only if you know in advance where the crisis is going to turn up.
     The extreme difficulty of changing course in space means that you cannot hang around in a trouble spot and be ready to give chase if something comes up. The mere size of space means that there isn't going to be any narrow region of space you can keep an eye on to keep most trouble under wraps, unless that region is in orbit around a planet.

Clay: "This has always struck me as the major flaw in single laser configurations—the assumption that the enemy won't just buckshot you to death."

     I think there is practically no point defense that can help against buckshot. Even a small amount of armor, however, can.

Byron: "My overall view on this is that any sort of presence patrol will be in the form of a station, not individual ships."

     A fleet of ships can be in several places at once, which is useful when you're trying to keep an eye on an entire planet. I don't think a patrol craft benefits that much from being large, except in as far as that it gives you more room for crew amenities to endure the long boredom.

BYRON:
     Milo, you misunderstand what I meant. I was trying to say that a long-term patrol won't be carried out by ships on rotation from a home base at a different planet. Instead, a base will be constructed in the system, and ships will be more-or-less permanently assigned there while the crews rotate.
     The problem is that to be capable of carrying a crew on an interplanetary voyage, a patrol craft will have to be large. My stations solve that, as they only have to deal with the normal crew under peacetime conditions for a month or two at most. If you need to move it back home for a refit or something send a skeleton crew.

TONY:
     Milo, the whole point of patroling is that you don't know when or where the crisis is going to be, so you maintain a presence where you have an interest, ready to react when one does.
     Also, the size of space and the difficulty in changing direction dictates precisely that you can only focus on well-defined regions of interest. The only such well-defined regions are those within tactically relevant distance of a point of interest, like a planet or an asteroid. Anyplace else has little if any strategic value and just ain't worth fighting over -- not that anybody would go there in the first place.
     About the only situation in which you might get combat away from natural bodies is if two powers launch comparable warships through the same window at the same destination, and either one or both ofthem had enough spare delta-v to maneuver into combat, fight it out, and still make any necessary orbital correctios and orbital insertions at the destination.

CLAY:
     Milo, Ahhh, but that small amount of armor isn't so small given mass constraints. Even a little—and we don't know ahead of time how "little" it gets to be because we don't know what the scenario will be—can radically reduce the overall amount of Delta-v available, or else run up the price tag.
     And there's a Catch-22 with up-armoring your ship. Once you do a little, and the price goes up, then you feel the need to protect it even more since now that ship represents a bigger investment. And so on and so forth.
     And yes, I know a big laser is theoretically better than several small ones, but it also puts all your eggs in one basket. Again, you don't need to destroy big-gun patrol ships with buckshot, you just need to screw up their mirror or mess up their radiators, etc…
     That's the problem with space warships. They're like flying aircraft carriers in modern war. Theoretically useful, but too vulnerable to justify the expense.
     In this case, we either have real warships or automated spysats. Why build a ship that isn't powerful enough to really fight, only to take a look at stuff that can be observed at far less cost by automated spysats.
     Even if there is trouble, the patrol vessel isn't really a warship. It will quickly get overwhelmed, and it won't take much to do it.

MR. BLUE: Don't forget one very important role for Patrol Ships: Deep Space Search and Rescue. Think of it as an analog to today's Coast Guard cutters.
     So, the espatiers would be have a good levening of Pararescue types to effect rescues inside damaged ships. Add a pretty good trama center onboard ship.
     The ship would need to be armed, but it would not really be used for classic warship to warship combat. You would mostly use the laser to vaporize or move any potentially hazardous debris. That laser would also come in handy if you needed to slag a fleeing smuggler or rogue missle.

RICK ROBINSON:

I will split my responses to points into mainly technical and mainly strategic.

Technical:

I've come to be doubtful that armor is worth the mass penalty. Any kinetic strike that saturates a decent laser defense will probably overkill the target, while a laser will zero in on vulnerable points rather than just zap away at armor.

For the same reason, military craft might not look much different overall from civil ships, apart from the actual weapon mounts.

The advantage of range (and more zapping intensity at any given range) justifies a single main mirror, I think. Tanks have one main gun, and they are much more subject to being engaged from an unexpected bearing.


I like the idea of being able to detach sections. There are some mass penalties, but mostly pretty minor ones. One constraint, in my presumed tech, is that the laser draws electric power from the main drive, so is necessarily connected to it.

For interplanetary missions the distinction between 'ship' and 'station' is quite blurred. Attach a drive bus to a station and it becomes a ship; remove the drive bus from a ship and its hab becomes a station.


Strategic:

The ship I outlined is not intended for 'combat patrols.' In an all-out shooting war the patrol ships may as well be mothballed for the most part.

They are intended for missions more comparable to those of coast guard cutters, Victorian gunboats, and Teddy Roosevelt era 'peace cruisers.' Basically wherever a polite request and a 20 MW laser will get more compliance than the polite request by itself would.

So the armament is not primarily to engage peers but to provide a clear dominance over jury-rigged or other light armament.

Whether there is a valid mission for these ships is a valid question. To be strictly realistic, there probably won't be anything beyond Earth orbital space but research stations, and an extremely minimal military/police presence comparable to Antarctica today.

But if you are going to assume a future Solar System filled with all sorts of activities, power players are going to want intermediate coercive options between sternly worded protests and interplanetary kinetic/nuclear strikes.

• 

The comment thread on my previous post about space patrols raised the issue of base stations for more prolonged missions, extending to years.

This has application far beyond military or quasi-military patrols. In fact it is fairly fundamental to any extensive, long term human presence in deep space. Whether or not we put permanent bases on the surface of Mars, Europa, or wherever, we will surely place permanent or semi-permanent stations in orbit around them. Particularly because the stations can be built in Earth space, where the industry is (at least initially), and flown out to where they will serve.

Hab structures intended for prolonged habitation should be fairly large, if only because if you are going to live for years in a can it should be at least be a roomy one. And they must be thoroughly shielded against radiation, much more than ships that you only spend a few months aboard every few years.

So let us play with some numbers. Make our spin hab a drum, 200 meters in diameter and 100 meters thick. Volume is thus about 3.14 million cubic meters. The ISS has about 1200 m3 of pressurized volume and a mass of some 300 tons, for an average density near 0.25, but the mass includes exterior structures such as keel and wings. Let average interior density be about 0.16, for a mass of 500,000 tons.

If we allow 100 cubic meters per person the onboard population (whether 'crew' or simply residents, or a mix) can be up to 30,000 people. This is about twice the density of a middle class American urban apartment complex. Given that much of the usable volume must be working areas, public spaces, and so forth, the actual crew or population might be more on the order of 10,000 people, equivalent to a decent sized small town or a fairly large university or military base. Thus the hab has 10 times the volume of an aircraft carrier and twice as many people.

Spin the hab at 3 rpm and you get almost exactly 1 g at the rim.

By my general rule the cost of this hab is on order of $500 billion. That is a steep price tag, but on the other hand it is only five times the cost of the ISS, and you need very few of these unless you are engaged in outright colonization.

Now, shielding. The standard for indefinite habitation is about 5 tons per square meter of cross section. (Earth's atmosphere provides about 10 tons/m².) Portions of the hab where people do not spend much time, and exterior to where they do spend time, can be counted toward the shielding allowance. So let us say that the outer 10 meters of the interior (about 35 percent of the volume) are used for storage, equipment rooms, and the like. This provides about 2 tons per square meter of shielding, 40 percent of the requirement.

The remaining 3 tons per square meter of exterior shielding must cover about 125,000 square meters of surface, so shielding mass is about 375,000 tons, adding 75 percent to the mass of the hab, now 875,000 tons. This shielding need not be 'armor.' As I recall, water provides pretty good shielding against GCRs, your biggest radiation problem, and water is so useful that having 375,000 tons of it on hand in a reservoir will never be amiss.

Moreover, to move the hab you can vent off the water (or pump it out) and not need to lug the mass, assuming you can replace it wherever you are going. The deep interior of the hab, more than 25 meters from the surface (about 28 percent of the volume) is still shielded by the rest of the hab structure, so the hab can carry a reduced population during the transfer.

You are still moving a half million ton payload, so don't expect to rush it unless you have a really badass drive bus handy. Habs being repositioned across the Solar System probably travel on Hohmann orbits, and have drive accelerations of a few dozen microgees, good for about 1 km/s per month of steady acceleration.

For a smaller hab structure, scale down the linear dimensions by half, to 100 meters diameter and 50 meters thick. Structural mass, volume, and capacity are all reduced by a factor of 8, to 400,000 cubic meters, 60,000 tons, and a crew / resident population of about 1500-4000. Our 'mini' hab is now broadly comparable in volume, mass, and crew to an aircraft carrier.

Surface area is only reduced, however, by a factor of four, to about 30,000 square meters. Moreover, the smaller hab provides less interior self-shielding. If we keep the same proportions our internal reserved zone is just 5 meters deep and provides only 20 percent of the needed protection, not 40 percent.

We now need about 120,000 tons of shielding — twice the unshielded mass of the hab. If we move the hab fully shielded our payload mass is 180,000 tons. Remove the shielding and payload mass is just 60,000 tons, but no part of the smaller interior is fully self-shielded, so any crew on board during a 'light' transfer must be relieved every few months. On the bright side, if you have a 100 gigawatt drive bus floating around, or about $100 billion to buy one, you can take a fast orbit and get there in a few months.

The image shows a drum-hab station ship with a spin hab of the full sized type described above, 200 meters in diameter by 100 meters thick, fitted with a heaviest class drive bus for transfer. I am delicately ignoring details of the connection between the spin drum and the hub structures.

The shuttles approximate the NASA Shuttle, as a visual size reference. The deep space ships docking up to it are large fast transports, 300 meters long, ten times heavier than the patrol ship discussed last post. The station ship itself is about 675 meters long by 450 meters across the outrigger docking bays.

In my image the station ship is no aesthetic triumph. Allowing for my limitations as an graphic artist (compare to commenter Elukka, from the last comment thread), the transport class ships don't look too bad, but the station ship merely looks tubby instead of grand. Some modest architectural improvements might yield a more impressive appearance with little change in overall configuration.

Of course the interior will matter immeasurably more to the people on board. Mostly, presumably, it will resemble the interior of a very large oceangoing ship, corridors and compartments, probably including some fairly imposing public spaces, comparable to the grand saloon of a 20th century ocean liner or even larger. It can be as elegant or as sterile as you like (or both, depending on deck and sector). The third popular choice, rundown industrial gothic, is constrained by how far you can go in that direction before the algae dies or the air starts leaking out.

• 

Ray McVay Rocketpunk Patrol Ship
Dry Mass	76.2 metric tons
Wet Mass	384.6 metric tons
Mass Ratio	5
Length Z	73 meters
Length Y	20.1 meters
Length X	15.2 meters
Engine	x2 F-26-A LH/LOX
Thrust	7.7×106 N
Acceleration	0.5 g
ΔV	8,200 m/s

This is the same one from the other day, only dressed up with a nice logo and some stats. These are realistic capabilities made courtesy of the charts and other information available from Atomic Rocket and inspiration from Rick Robinson's Rocketpunk Manifesto.

My PL differs from the one in Rick Robinson's article in a few key areas. The main difference is that it is not made for long hauls. It only has a delta v of about 8200 m/s. This will not get one far in the solar system but it allows a forward deployed Patrol Craft a sufficient "range" to perform many of the missions we discussed in the last post on Building a Space Navy. Our little A-Class has enough Delta V to shape a light-second orbit around a convoy in deep space, conduct SAR missions anywhere in cis-lunar space, or to reach any moon of Saturn from any other moon. Obviously, this rocket is mostly propellant (mass ratio 5). If you drew lines through the side view of the rocket that bracket the docking rings, you would encompass the entire pressurized volume. I've got to say, it's nice to work on a warship for a change — I don't have to make it economical to run!

One of the interesting things about this design is actually the freedom the little carried craft gives me. It was a throw-away touch, originally — a design borrowed from another project. But as I got to looking at the little thing, I realized that it's about the size of the Saturn V stage/Apollo/LM stack. That means it should be able to go from Earth Departure to Lunar orbit. That means that it has the Delta V to ferry crew to and from a Patrol Craft on station away from the convoy. That means, like submarines, our Patrol Craft can have two crews and stay out for a lot longer than otherwise. This is one of those realistic touches that I hope add to the charm of the rocket's design.

ed note: a 1500 nanometer near infrared laser with a 10 meter fixed mirror can have a 4 centimeter spot size out to 220 kilometers or so. A 4 meter mirror can have a 4 centimeter spot size out to 87 kilometers or so.

COMPLIANCE WITH THIS PUBLICATION IS MANDATORY

• 1. Requirements and Procedures.
  • 1.1. Tamper Control Program. The Two-Person Concept (TPC) is central to nuclear surety tamper control measures in the Air Force. It is designed to make sure that a lone individual cannot perform an incorrect act or unauthorized procedure on a nuclear weapon, nuclear weapon system, or certified critical component.
  • 1.2. Concept Enforcement. Each organization with a mission or function involving nuclear weapons, nuclear weapon systems, or certified critical components:
    • 1.2.1. Identifies no-lone zones (where at least two authorized persons must be present during any operation or task).
    • 1.2.2. Enforces the Two-Person Concept.
    • 1.2.3. Develops procedures to limit entry to authorized persons who meet the requirements of paragraph 1.3.
  • 1.3. Team Requirements. (Refer to paragraph 1.6.1 for criteria on foreign nationals.) A TwoPerson Concept team consists of at least two individuals who:
    • 1.3.1. Are certified under the Personnel Reliability Program (PRP), as specified in DoD 5210.42-R_AFMAN 10-3902, Nuclear Weapons Personnel Reliability Program.
    • 1.3.2. Know the nuclear surety requirements of the task they perform.
    • 1.3.3. Can promptly detect an incorrect act or unauthorized procedure.
    • 1.3.4. Have successfully completed nuclear surety training according to AFI 91-101, Air Force Nuclear Weapons Surety Program.
    • 1.3.5. Are designated to perform the required task.
  • 1.4. Two Person Concept Violations. Report a Two-Person Concept violation when a lone individual in a no-lone zone has the opportunity to tamper with or damage a nuclear weapon, nuclear weapon system, or certified critical component. Refer to AFMAN 91- 221, Weapons Safety Investigations and Reports, for reporting guidance.

After arriving at the LCF, a missile crew had their identification examined by the flight security controller and then began the authentication procedure with the on-duty missile crew. After they cleared security, they descended down the elevator to the LCC, also known as the "no-lone zone," because one could never enter the capsule alone. After arriving at the blast door a voice would shout "clear" from inside the capsule. The oncoming crew shouted back and the eight-ton door slowly swung open.

Once inside the capsule, the missile crew's shift began during a process called changeover, a formal procedure that allowed for the changing of crews in the LCC. The changeover included a ten-minute briefing on the weather report, call signs, a classified advisory on the day's war plan, and the placement of each crew member's padlock on the metal box that secured the launch keys. The changeover concluded with each departing crew member handing over three items to the deputy and commander— a three-by-five inch card encased in plastic and framed in metal with the day's top secret code to decipher commands from SAC; a key to be inserted into the console and turned in order to fire the missiles; and a .38-caliber revolver. The gun, worn in a holster, was for protection in the unlikely event of intruders. The missile combat crew was prohibited from taking off the holster while in the capsule.

After the capsule door closed, a new crew would check the maintenance logs and inspect support equipment. The duration of their shift was spent running practice drills or reviewing procedures to prepare for SAC's random Operational Readiness Inspections, an examination performed by an Inspector General to determine the effectiveness of the combat crews. The crew had very precise procedures for every task. If they ever received a launch command, both crew members would open the locked box that contained "cookies," or the authentication codes. Once the crew members agreed that the command was authentic they would insert the keys and turn them at the same time, launching a missile.

To launch a missile, an Emergency War Order (EWO) would have come over the SAC radio with a message that the crew had to authenticate. After they agreed that the message was authentic, they unlocked their padlock on the red metal box that contained two keys for launching the missiles. Each crew member would then buckle into their seats and the commander would count down. The deputy commander then flipped a row of "arming" switches for each of the missiles, making them readied for immediate launch. The commander opened the plastic cover over his launch control panel in front of him exposing the area for the launch key, and the deputy commander removed the plastic cover over the cooperative launch switch. Each crew member would insert their key and a "conference call" is ordered where the crew speaks via phone and headset to the squadron command post for readiness reports on other Minuteman capsules. The command post then issues a command to "launch on your count." On the commander's count, both crew members would have to turn the keys at the same moment. The two ignitions are situated far enough apart that one person alone could not reach both keys and single-handedly provide the go ahead to launch a missile. The Minuteman missile cannot be launched without a corroborating signal from another LCC, providing the second vote. Launch procedures were modified slightly in later years when a launch enable control group signal panel was added to the Deputy Commander's Control Console. An unlock code was required to be inserted into the "code inert thumbwheel switches" of the launch enable control panel to enable missiles for launch.

(ed note: Isaac Kuo is of the opinion that standard Orion pulse units are sub-optimal for asteroid deflection.)

Given the extreme expense of the sort of nuclear bombs required for an Orion style propulsion system, and the stupendous cost of developing it, I don't think it's a good idea to develop it (there are numerous practical problems with using it, even if there were a budget to perform a mission with it).

In contrast, off the shelf nuclear bombs suitable for asteroid deflection have already been developed. The main expense is the weapons grade fission primary (which Orion style drives need oodles of), but the power of a nuke can be upscaled using cheap lithium deuteride stages — and using cheap waste U238 for the casing/tamper/etc. This results in a powerful nuclear bomb which spits out mostly neutrons — pretty useless for an Orion style drive, but ideal for asteroid deflection. These neutrons will penetrate into the asteroid and cause a nice layer of the asteroid to vaporize — producing thrust in an energy efficient (but mass inefficient) way.

This is the opposite of what you want for an Orion style drive. You do NOT want to vaporize the pusher plate of an Orion style drive, and if you're going to do something so mass inefficient you might as well use a low performance chemical rocket propulsion system instead.

Basically, the parameters of what's desirable for asteroid deflection and what's desirable (or even sensible) for an Orion style drive are too radically different. For asteroid deflection, it's actually good to have a specific impulse in the low triple digits (i.e., on par with chemical rocket I_sp). This minimizes the energy required, and this in turn, reduces the mass of the nukes needed to deflect the asteroid. So what if you have to vaporize a significant fraction of the asteroid to do the mission?

And an Orion style drive does not play well with the fast neutrons of a lithium deuteride bomb. Fast neutrons penetrate a pusher plate...even if you downscale the nuke enough so it won't outright vaporize the pusher plate, the neutrons will cause damage. Lithium deuteride is good because it is much cheaper than fission bomb material and it gives more bang for a given amount of mass as well. The nice thing about upscaled fusion bombs is that the size/mass of the primary remains fixed (a fixed cost), while the additional lithium deuteride is very very cheap in comparison. But you know what you get if you try and use a few humongous nukes instead of thousands of little nukes to push an Orion style rocket ship? You get a blown up rocket ship.

The use of a ²³⁸U casing/tamper/etc doesn't really mix well with an Orion style drive either. The neutrons from ²³⁸U aren't so fast, but there are oodles of them. This is great for asteroid deflection because the extra oomph from ²³⁸U is extra energy in neutrons that are still nicely penetrative.

Employees of the Department of Celestial Mechanics and Astrometry NII PMM and colleagues from St. Petersburg State University, Keldysh Research Center, and Research Institute Sirius are developing measures to protect the Earth from potentially dangerous celestial bodies. With the help of supercomputer SKIF Cyberia, the scientists simulated the nuclear explosion of an asteroid 200 meters in diameter in such a way that its irradiated fragments do not fall to the Earth.

- The way we propose to eliminate the threat from space is reasonable to use in case of the impossibility of the soft disposal of an object from a collision in orbit and for the elimination of an object that is constantly returning to Earth, - says Tatiana Galushina, an employee of the Department of Celestial Mechanics and Astrometry - Previously, as a preventive measure, it was proposed to abolish the asteroid on its approach to our planet, but this could lead to catastrophic consequences - a fall to Earth of the majority of the highly radioactive fragments.

TSU scientists with colleagues from other research centres have offered another solution to the problem. It is known that the majority of dangerous objects pass close to Earth several times  before the collision. Therefore, there is a possibility to blow up the asteroid at the time when it is farther from the planet. This measure will be much more effective and safer.

For computer modeling as a potential target was taken a celestial body with a diameter of 200 meters, similar to the asteroid Apophis, which in 2029 will approach Earth at a distance of 38,000 kilometers. Calculations have shown that for the destruction of the object there must be the impact of a nuclear device with energy of one megaton of TNT equivalent. In this case, part of the asteroid turns into gas and liquid droplets, and some will break into pieces no larger than 10 meters. This is the maximum in terms of safety for the Earth.

- Because the rocket catches behind the asteroid, almost all the pieces after the destruction will fly forward, - says Tatiana Galushina. - In this case the orbit of the fragments will be significantly different from the asteroid's orbit. For 10 years after the explosion an insignificant number of fragments will fall to Earth. Their radioactivity during this time will be reduced considerably, and after a few years they will not pose a danger. It is worth adding that nuclear explosions in space are prohibited by international treaty, but in the case of a real threat to humanity maybe there will be an exception to this rule.

Specialists from different areas who are experts in celestial mechanics and ballistics worked on the project. The scientists note that the theoretical calculations are only the beginning of the work, without which the practical implementation on the preventive measures protecting the Earth is impossible.

• 

A research collaboration between Lawrence Livermore National Laboratory (LLNL) and the Air Force Institute of Technology (AFIT) investigates how the neutron energy output from a nuclear device detonation can affect the deflection of an asteroid.

Scientists compared the resulting asteroid deflection from two different neutron energy sources, representative of fission and fusion neutrons, allowing for side-by-side comparisons. The goal was to understand which neutron energies released from a nuclear explosion are better for deflecting an asteroid and why, potentially paving the way for optimized deflection performance.

The work is featured in Acta Astronautica and was led by Lansing Horan IV, as part of a collaboration with LLNL’s Planetary Defense and Weapon Output groups during his nuclear engineering master’s program at AFIT. Co-authors from LLNL include Megan Bruck Syal and Joseph Wasem from LLNL's Weapons and Complex Integration Principal Directorate, and the co-authors from AFIT include Darren Holland and Maj. James Bevins.

Horan said the research team focused on the neutron radiation from a nuclear detonation since neutrons can be more penetrative than X-rays.

“This means that a neutron yield can potentially heat greater amounts of asteroid surface material, and therefore be more effective for deflecting asteroids than an X-ray yield,” he said.

Neutrons of different energies can interact with the same material through different interaction mechanisms. By changing the distribution and intensity of the deposited energy, the resulting asteroid deflection also can be affected.

The research shows that the energy deposition profiles — which map the spatial locations at and beneath the asteroid’s curved surface, where energy is deposited in varying distributions — can be quite different between the two neutron energies that were compared in this work. When the deposited energy is distributed differently in the asteroid, this means that the melted/vaporized blow-off debris can change in amount and speed, which is what ultimately determines the asteroid’s resulting velocity change.

Defeating an asteroid

Horan said there are two basic options in defeating an asteroid: disruption or deflection.

Disruption is the approach of imparting so much energy to the asteroid that it is robustly shattered into many fragments moving at extreme speeds.

“Past work found that more than 99.5 percent of the original asteroid’s mass would miss the Earth,” he said. “This disruption path would likely be considered if the warning time before an asteroid impact is short and/or the asteroid is relatively small.”

Deflection is the gentler approach, which involves imparting a smaller amount of energy to the asteroid, keeping the object intact and pushing it onto a slightly different orbit with a slightly changed speed.

“Over time, with many years prior to impact, even a miniscule velocity change could add up to an Earth-missing distance,” Horan said. “Deflection might generally be preferred as the safer and more ‘elegant’ option, if we have sufficient warning time to enact this sort of response. This is why our work focused on deflection.”

Connecting energy deposition to asteroid response

The work was conducted in two primary phases that included neutron energy deposition and asteroid deflective response.

For the energy deposition phase, Los Alamos National Laboratory's Monte Carlo N-Particle (MCNP) radiation-transport code was used to simulate all of the different case studies that were compared in this research. MCNP simulated a standoff detonation of neutrons that radiated toward a 300 m SiO₂ (silicon oxide) spherical asteroid. The asteroid was divided by hundreds of concentric spheres and encapsulated cones to form hundreds of thousands of cells, and energy deposition was tallied and tracked for each individual cell in order to generate the energy deposition profiles or spatial distributions of energy throughout the asteroid.

For the asteroid deflection phase, LLNL’s 2D and 3D Arbitrary Lagrangian-Eulerian (ALE3D) hydrodynamics code was used to simulate the asteroid material’s response to the considered energy depositions. The MCNP-generated energy deposition profiles were imported and mapped into the ALE3D asteroid in order to initialize the simulations. The resulting deflection velocity change was obtained for various configurations of neutron yields and neutron energies, allowing for the effect of the neutron energy on the resulting deflection to be quantified.

One small step for deflection

Horan said the work is one small step forward for nuclear deflection simulations.

“One ultimate goal would be to determine the optimal neutron energy spectrum, the spread of neutron energy outputs that deposit their energies in the most ideal way to maximize the resulting velocity change or deflection,” he said. “This paper reveals that the specific neutron energy output can impact the asteroid deflection performance, and why this occurs, serving as a stepping stone toward the larger goal.”

Horan said the research showed that precision and accuracy in the energy deposition data is important. “If the energy deposition input is incorrect, we should not have much confidence in the asteroid deflection output,” he said. “We now know that the energy deposition profile is most important for large yields that would be used to deflect large asteroids.”

He said if there were to be a plan to mitigate a large incoming asteroid, the energy deposition spatial profile should be accounted for to correctly model the expected asteroid velocity change.

“On the other hand, the energy coupling efficiency is always important to consider, even for low yields against small asteroids,” he said. “We found that the energy deposition magnitude is the factor that most strongly predicts the overall asteroid deflection, influencing the final velocity change more than the spatial distribution does.”

For planning an asteroid mitigation mission, it will be necessary to account for these energy parameters to have correct simulations and expectations.

“It is important that we further research and understand all asteroid mitigation technologies in order to maximize the tools in our toolkit,” Horan said. “In certain scenarios, using a nuclear device to deflect an asteroid would come with several advantages over non-nuclear alternatives. In fact, if the warning time is short and/or the incident asteroid is large, a nuclear explosive might be our only practical option for deflection and/or disruption.”

• 

ABSTRACT

An earth protection system against asteroids and meteorites in colliding orbit is proposed. The system consists of detection and deorbiting systems. The analyses are given for the resolution of microwave optics, the detectability of radar, the orbital plan of intercepting operation, and the antimatter mass required for total or partially blasting the asteroid. Antimatter of 1 kg is required for deorbiting asteroid of 200 m in diameter. An experimental simulation of antimatter cooling and storage is planned. The facility under construction is introduced.

INTRODUCTION

     The space activities of mankind have been supported by

     1) curiosity in sense to find new laws of universe and in exploration to find new world.

and will be so in future. Another motivation of space activities especially in future is

     2) desire to preserve the human race, i.e. instructive move for survival.

The second motivation may take the form of Solar Power Satellite (SPS) and human resource exploitation, i.e. helium 3. These are counter action against the energy crisis coming in future. The energy crisis is related to the expansion of human activities. On the other hand, there is another type of crisis, the natural disaster caused by asteroid collision with the earth.

     Asteroids approaching to the earth have so high relative velocities about 30 km/s that the kinetic energy is extremely large even if it is much smaller than the earth. Asteroids collision with the earth result in not only the craters formation and tidal waves but also the earth environment modification. The Hiroshima atomic bomb has an energy of 10¹⁵ J, which corresponds to the estimated kinetic energy of a meteorite, 10 m in diameter and 5 in specific gravity. Celestial body in 10 m class crashes on the earth once every several hundreds years. It is reported that a collision with a meteorite in the Cretaceous period changed the climate and exterminated the dinosaur in the mass. The collision correspond3 to 5 billion Hiroshima bombs. The asteroid collision equivalent to the dinosaur extinction happens once per 100 million years.

• 

Asteroids very frequently near-miss the earth as shown in Fig.1. Figure 1 is not a complete list since the asteroids in Fig.1 were accidentally observed by voluntary observers. The 1989 FC passing by the earth on March 22 in 1989, had several times as large kinetic energy as the asteroid which formed the Arizona's famous 1.2km meteor crater.

     Antimatter annihilation propulsion for interstellar and deep space missions has been recently studied because of high energy density of antimatter-matter reactions. Most of the studies emphasize the mission analyses and the conceptual designs of antimatter engines. On the other hand, we have been studying the storage of the antimatter and considering the application of the earth protection system against asteroid collisions.

     The asteroids uf 10-100 m size, which had impinged in the ocean and caused global weather impact, may not be recorded in the history books.

     The earth protection system presented here not only actively detects the celestial bodies approaching to the earth but also modifies their orbit. The objectives of this paper are:

     1) to estimate distance to detect asteroids from the earth and remaining time before collision,

     2) to estimate requirements for radar system characteristics using Very Long Base Line Interfercmetry (VLBI),

     3) to estimate the amount of antihydrogen for the orbital modification of meteorites,

     4) to examine antimatter storage,

     5) to design the antimatter factory and base.

REMAINING TIME BEFORE ENCOUNTER

     In order to make the analysis simple, three dimensional effects such as the inclination of the asteroid orbit are ignored. Meteorites are either comets or minor planets. Based on orbital data of comets, the eccentricities are found around 0.8 and the distance of perihelion ranges from 0.13 to 0.98 a.u..

• 

Figure 2 shows the relation between the remaining time and the distance. The asteroid is assumed to move frem the aphelion toward the orbit of the earth in the calculation. While the orbital radius distributes from 2 to 3 a.u. in the case of meteorites which are categorized as minor planets. It is concluded from these results that the distance to have to detect the asteroid is 1 a.u. and the remaining time before encounter is from 2 to 3 months.

RADAR SYSTEM BY VLBI

     The radar system is required to detect and track an object approaching to the earth as soon as possible. Suppose the asteroid of 100 m in diameter is detected at 1 a.u. distance from the earth. A great number of celestial bodies are observed by the photographic method with large telescopes. Asteroids approaching to the earth are discovered and tracked by the radar. The precision for the tracking radar requires 0.1 nrad in angular resolution. Such a resolution can be achieved by VLBI in radio astronomy such as VSOP (VLBI Space Observatory Program) in Institute of Space and Astronautical Science (ISAS). For the purpose of determination of transmission power of microwave, wave length, diameter of antennas and baseline distance, it is assumed:

     1: Antenna for microwave transmission are the same size as receptive one.

     2: Receptive sensitivity is 10^-20W.

     3: Microwave is scattered at the asteroid's surface uniformly and isotropically.

     4: Reflectivity of asteroids is 0.1.

The first assumption is made only for convenience. The second precision corresponds to an observation of a radio galaxy with 1 mJy (1Jy=10^-26Wm^-2Hz^-1) by a radio telescope which is 100 m in diameter and 100 kHz in band width. The third assumption is very natural since the surface unevenness is larger than the wave length. The reflectivity of Apollo objects is assumed to be 0.1.

     Now we derive the relation between the transmitted and the received power. Microwave beam diverges with transmitting distance. The theoretical minimum for beam collimation is given by

A: cross sectional area of microwave beam
L: distance between asteroid and the earth
d: diameter of transmit and receptive antenna
λ: wavelength of microwave.

The power received by the receptive antenna is given by the equation

P_a : received microwave power
P_t : transmitted microwave power
δΩ : solid angle of receptive antenna measured from asteroid
D : asteroid diameter

The angular resolution of VLBI can be estimated to be the order of λ/L. The power required for each satellite is about 10 kW if the millimeter wave is transmitted at 10 Hz repetition with the pulse width of 10 μs. The required characteristics of the radar system are summarized in Table 1.

Table 1: Specifications of the Radar System
diameter of asteroid	100 m
diameter of antennas	25 m
received power	10-20W
wave length	0.1 mm
peak power of microwave	100 MW
number of transmission satellites	10
baseline distance	1000 km

As exhibited in Table 1, these satellites are only 2.5 times larger than that of the VSOP in size. The surface accuracy of the receptive antenna, however, will be required at least 2 order of magnitude higher than that in VSOP since the parabolic surface of the VSOP is controlled to maintain within the small displacement of 0.1mm. It is indicated that additional difficulties are found by the VLBI of millimeter range at present.

ANTIMATTER REQUIRED FOR MODIFICATION OF ASTEROID ORBIT

     For small asteroids, the interceptors loaded with the antihydrogen can destroy them completely. If the asteroid is too large to be entirely exploded, it is necessary to penetrate into the celestial body and blast off the surface materials effectively. It is estimated in the case of orbital change using explosion that the energy utilization efficiency is less than 1% i.e. the ratio of the exploded mass to the remaining mass of the asteroid.

     The antimatter-matter annihilation generates shock wave and produces high energy plasma at the center of the explosion. If the plasma dissipates its energy to surrounding materials efficiently, lava with high energy will be blasted off. The reaction against the astereid produces the thrust. The energy E generated by the annihilation is related:

ρ : asteroid density
r : diameter of lava region ( depth of penetration )
M : asteroid mass
ΔV_melt : effective velocity corresponding to melting energy
U : mean velocity of lava

The first term of the right hand side of Eq.(3) represents the internal energy and the second one does the kinetic energy of the lava. It is assumed that a half of the lava blasts and contributes to the orbital modification, and the rest half merely heats up surroundings. The velocity change V and the efficiency η are calculated:

The radius r is a control parameter of the explosion (or thrust generation). Choosing r so as to maximize the efficiency:

are obtained as the optimum velocity change and penetrating depth. For example, the optimum depth is estimated to be 240 m from Eq.(7) for the antihydrogen of 1 kg.

• 

     Figure 3 shows the relation between the mass of the antihydrogen and the delta-V calculated from Eq.(4). A value of 1m/s is the minimum delta-V required for the orbital change if the orbit is modified at 1.3 a.u. distance from the sun. Generally, the minimum delta-V is a function of the orbital elements, the direction of the thrust and the distance from the earth.

• 

The closest distance between the earth and the asteroid is plotted in Fig.4 with thrusting directions as parameters. The optimum direction is either parallel or anti-parallel to the orbiting direction of the asteroid. The delta-V at ϑ=π/3 is ten times as high as that at ϑ=0 for given distance.

• 

Figure 5 shows the closest distance as a function of delta-V on deorbiting position as parameter. The delta-V required for 1.55×10⁸km is ten times as large as that for 2×10⁸km. As the farther distance the orbit is modified, the smaller the delta-V is required. This means the importance of the early detection and the orbital modification as soon as possible.

ANTIHYDROGEN STORAGE

     At present, antiprotons are generated by the method of a collision between a heavy metal target and a proton beam which is accelerated up to several tens of GeV or more. Reference 8 reports that 10¹¹ antiprotons (~pg) are obtained per hour in Fermilab. The productive amount of the antiprotons has been increased at the rate of 10 times per 3.5 years ever since the discovery by Segre and Chamberlan so that the antiproton will be available industrially in 2020's if it monotonically increases (sadly, this did not happen). It is necessary that the antimatter is stored as solid antihydrogen at cryogenic temperature since the antimatter required for the orbital modification amounts to the order of kg or more as seen in Fig.3.

• 

     The storage processes are shown in Fig.6. At first, the produced antiparticles are cooled by stochastic and electron coolings because antiprotons are tremendously hot Just after they are generated by an accelerator. They are decelerated as slow as several keV and are turned into the antihydrogen by three body recombination with cold positrons. The unrecombined particles are cycled in the antiproton and positron rings being collimated with accelerator and electrostatic lens. The resultant antihydrogen beam is decelerated and trapped by means of laser cooling. A vacuum ultraviolet CW laser for the hydrogen cooling have not been accomplished yet, but will be put to practical use in near future with stable multi-ionized ion sources recently accomplished. Solid antihydrogen is produced from the trapped antihydrogen, and is stored electrostatically.

     Experimental demonstration is in progress with respect to the recombination and the deceleration of the antihydrogen. The antihydrogen is simulated by ordinary matter argon in the experiment, since antiparticle can be regarded as particle with opposite charge without annihilation. Except for the differences in the mass and the energy level for the laser cooling, the argon in a metastable state has the advantage of being incorporated with laser diode, which has energy level related to near infrared range. The photograph of the experimental apparatus is shown in Fig.7. It consists of a plasma source which simulates a low energy antiproton beam, a recombination chamber, a cooling and trapping chamber.

ANTIMATTER FACTORY AND INTERCEPTOR BASE

     Necessary conditions for establishing the antimatter factory and the interceptor base comprises;

     1: Sufficient solar power can be easily obtained,

     2: Energy to launch the interceptor is small,

     3: The earth's safety is assured at an accident.

The construction of the factory farther than the Mars orbit from the sun is not beneficial since the SPS (Solar Power Satellite) collects solar energy to produce antimatter. Lagrange points of L4 and L5 between the sun and the earth have the advantage of the minimum launching energy since they are the points of the gravitational equilibrium. It is also convenient from following stand-points to construct the plant on the back side of the SPS. First, the plant is cooled down as cryogenically as the space back ground temperature of 3 K because of isolation from the solar energy flux. Second, the high vacuum environment keeps the loss rate of the stored antimatter low because of low background density, a few particles per cm³. Even if the disaster by the annihilation occurs in the plant, the irradiation from the antimatter factory remains as low as several times of natural level at the earth with 150 million km (1 a.u.) distance between the earth and the plant.

     Next we estimate the antimatter fuel to be changed in the interceptor. Suppose the interceptor encounters the asteroid at 200 million km from the sun in 30 days after launch. The necessary delta-V is about 30 km/s when the interceptor is launched in the same dlrection as the earth evolution, and about 90 km/s in the opposite direction. As for the latter mission, it is impossible for chemical rockets because of large payload mass ratio of 10⁹. However, antimatter engine enables such a mission since the specific impulse can be chosen just like electric propulsion and the thrust density is as high as that of the chemical rocket. Forward indicates that the payload mass ratio of the antimatter rocket do not exceed 5.

     The mass of the vehicle, m is assumed as 1 ton including an apparatus for the antimatter storage. Energy utilization efficiency ε by the antimatter-matter reactions is assumed as 0.32. The necessary antimatter is given by

m_v : mass of vehicle included an apparatus for antimatter storage
m_a : mass of antimatter propellant
ε : energy utilization efficiency by annihilation
ΔV : mission delta-V
c : speed of light

Substituting ΔV=90km/s into Eq.(8), the required amount of the antimatter is 0.1g at most, which is negligible compared with that for the orbital modification of the asteroid. The mass of the reaction fluid is 4 ton. Consequently, the launching from the antimatter base located on the Lagrange points is possible. The earth protection system is schematically shown in Fig. 8.

• 

CONCLUSION

     First, necessity of the earth protection system against the meteorite collisions is investigated. The designed system consists of the VLBI radar tracking system, the antimatter plant and the interceptor to modify asteroid orbits. The radar tracking an asteroid by means of VLBI is feasible considering the state of arts of required technology. Some issues of millimeter wave remains open. An experimental simulation for the antimatter storage is introduced. It is desirable to construct the antimatter plant and the interceptor base combining the SPS at the Lagrange point. Destruction or orbital change of asteroids is concluded to be impossible without use of the annihilation energy.

• 

A gravity tractor is a theoretical spacecraft that would deflect another object in space, typically a potentially hazardous asteroid that might impact Earth, without physically contacting it, using only its gravitational field to transmit the required impulse. The gravitational force of a nearby space vehicle, though small, is able to alter the path of a much larger asteroid if the vehicle spends enough time close to it; all that is required is that the vehicle thrust in a consistent direction relative to the asteroid's path, and that neither the vehicle nor its expelled reaction mass come in direct contact with the asteroid. The tractor spacecraft could either hover near the object being deflected, or orbit it, directing its exhaust perpendicular to the plane of the orbit. The concept has two key advantages: namely that essentially nothing needs to be known about the mechanical composition and structure of the asteroid in advance; and that the relatively small amounts of force used enable extremely precise manipulation and determination of the asteroid's orbit around the sun. Whereas other methods of deflection would require the determination of the asteroid's exact center of mass, and considerable effort might be necessary to halt its spin or rotation, by using the tractor method these considerations are irrelevant.

Advantages

A number of considerations arise concerning means for avoiding a devastating collision with an asteroidal object, should one be discovered on a trajectory that were determined to lead to Earth impact at some future date. One of the main challenges is how to transmit the impulse required (possibly quite large), to an asteroid of unknown mass, composition, and mechanical strength, without shattering it into fragments, some of which might be themselves dangerous to Earth if left in a collision orbit. The gravity tractor solves this problem by gently accelerating the object as a whole over an extended period of time, using the spacecraft's own mass and associated gravitational field to effect the necessary deflecting force. Because of the universality of gravitation, affecting as it does all mass alike, the asteroid would be accelerated almost uniformly as a whole, with only tidal forces (which should be extremely small) causing any stresses to its internal structure.

A further advantage is that a transponder on the spacecraft, by continuously monitoring the position and velocity of the tractor/asteroid system, could enable the post-deflection trajectory of the asteroid to be accurately known, ensuring its final placement into a safe orbit.

Limitations

Limitations of the tractor concept include the exhaust configuration. With the most efficient hovering design (that is, pointing the exhaust directly at the target object for maximum force per unit of fuel), the expelled reaction mass hits the target head-on, imparting a force in exactly the opposite direction to the gravitational pull of the tractor. It would therefore be necessary to use the orbiting-tractor scheme described below, or else design the hovering tractor so that its exhaust is directed at a slight angle away from the object, while still pointing "down" enough to keep a steady hover. This requires greater thrust and correspondingly increased fuel consumption for each metre per second change in the target's velocity.

Issues of the effect of ion propulsion thrust on the dust of asteroids have been raised, suggesting that alternative means to control the station keeping position of the gravity tractor may need to be considered. In this respect, solar sails have been suggested.

According to Rusty Schweickart, the gravitational tractor method is also controversial because during the process of changing an asteroid's trajectory the point on Earth where it could most likely hit would be slowly shifted across different countries. It means that the threat for the entire planet would be minimized at the cost of some specific states' security. In Schweickart's opinion, choosing the way the asteroid should be "dragged" would be a tough diplomatic decision.

Example

To get a feel for the magnitude of these issues, let us suppose that a NEO of size around 100 m, and mass of one million metric tons, threatened to impact Earth. Suppose also that

• a velocity correction of 1 centimetre per second would be adequate to place it in a safe and stable orbit, missing Earth
• that the correction needed to be applied within a period of 10 years.

With these parameters, the required impulse would be: V × M  = 0.01 m/s × 10⁹ kg = 10⁷ N-s, so that the average tractor force on the asteroid for 10 years (which is 3.156×10⁸ seconds), would need to be about 0.032 newtons. An ion-electric spacecraft with a specific impulse of 10,000 N-s per kg, corresponding to an ion beam velocity of 10 kilometres per second (about 20 times that obtained with the best chemical rockets), would require 1,000 kg of reaction mass (xenon is currently favored) to provide the impulse. The kinetic power of the ion beam would then be approximately 158 watts; the input electric power to the power converter and ion drive would of course be substantially higher. The spacecraft would need to have enough mass and remain sufficiently close to the asteroid that the component of the average gravitational force on the asteroid in the desired direction would equal or exceed the required 0.032 newtons. Assuming the spacecraft is hovering over the asteroid at a distance of 200 m to its centre of mass, that would require it to have a mass of about 20 metric tonnes, because due to the gravitational force we have

Considering possible hovering positions or orbits of the tractor around the asteroid, note that if two objects are gravitationally bound in a mutual orbit, then if one receives an arbitrary impulse which is less than that needed to free it from orbit around the other, because of the gravitational forces between them, the impulse will alter the momentum of both, together regarded as a composite system. That is, so long as the tractor remains in a bound orbit, any propulsive force applied to it will be effectively transferred to the asteroid it orbits. This permits a wide variety of orbits or hovering strategies for the tractor. One obvious possibility is for the spacecraft to orbit the NEO with the normal to the orbit in the direction of the desired force. The ion beam would then be directed in the opposite direction, also perpendicular to the orbit plane. This would result in the plane of the orbit being shifted somewhat away from the center of the asteroid, "towing" it, while the orbital velocity, normal to the thrust, remains constant. The orbital period would be a few hours, essentially independent of size, but weakly dependent on the density of the target body.

Abstract

     Given sufficient warning time, Earth-impacting asteroids and comets can be deflected with a variety of different “slow push/pull” techniques. The gravity tractor is one technique that uses the gravitational attraction of a rendezvous spacecraft to the impactor and a low-thrust, high-efficiency propulsion system to provide a gradual velocity change and alter its trajectory. An innovation to this technique, known as the Enhanced Gravity Tractor (EGT), uses mass collected in-situ to augment the mass of the spacecraft, thereby greatly increasing the gravitational force between the objects. The collected material can be a single boulder, multiple boulders, regolith or a combination of different sources. The collected mass would likely range from tens to hundreds of metric tons depending on the size of the impactor and warning time available. Depending on the propulsion system’s capability and the mass collected, the EGT approach can reduce the deflection times by a factor of 10 to 50 or more, thus reducing the deflection times of several decades to years or less and overcoming the main criticism of the traditional gravity tractor approach. Additionally, multiple spacecraft can orbit the target in formation to provide the necessary velocity change and further reduce the time needed by the EGT technique to divert hazardous asteroids and comets. The robotic segment of NASA’s Asteroid Redirect Mission (ARM) will collect a multi-ton boulder from the surface of a large Near-Earth Asteroid (NEA) and will provide the first ever demonstration of the EGT technique and validate one method of collecting in-situ mass on an asteroid of hazardous size.

Background

     A variety of techniques have been proposed to deflect asteroids and comets that could impact the Earth and cause destruction and loss of life. Efforts to deflect these hazardous Near-Earth Objects (NEOs) significantly benefit from early detection and precise orbit characterization. Warning times on the order of a decade or more significantly reduce the impulse, or velocity change (ΔV), needed to deflect an impacting NEO. Accurate knowledge of the object’s orbit is needed to confirm that the object will indeed impact the Earth, which is possible with a sufficient number of accurate astrometric observations along with the possible addition of precise radar measurements or the presence of an in-situ spacecraft. As shown in Figure 1, the application of approximately one cm/s (0.022 mph) of ΔV a decade before impact is typically required to allow for a one Earth radius deflection. This would be the minimum impulse required to just avoid a worst case impact that hits the Earth “dead center.” Additional ΔV would be required for margin against the orbit uncertainty or the NEO’s orbit would need to be more of a grazing impact to assure that the object misses the Earth. This ΔV increases by approximately an order of magnitude within a year of impact, and surpasses a meter per second in the last months before impact.

• 

Planetary defense techniques that can provide large, rapid impulses, such as kinetic impactors and nuclear detonations, require the least amount of warning time, but their effectiveness is dependent on the NEO properties, which are likely uncertain and vary substantially between objects. Additionally, the application of a large, concentrated force has the potential to fragment the NEO due to the unknown structure and mechanical properties of the target. These fragments could still be dangerous if they remain on an impacting trajectory with Earth. Techniques that can provide small, gentle impulses are much less likely to cause fragmentation, but typically require much longer interaction times (months to many years) to provide the necessary ΔV to deflect the impacting object. These “slow push/pull” techniques typically work by enhancing natural effects (e.g., albedo/thermal response modification via the Yarkovsky effect), by the ablation/expulsion of surface material, or by applying a contact or gravitational force. They are also effective against NEOs that are binary or even ternary systems. One consideration for these gradual deflection techniques is that when an impact with the Earth is confirmed, the exact impact point is still uncertain. This path of possible impact points, known as the “risk corridor,” is altered during a deflection effort with the impact point moving across the Earth’s surface as the impactor’s trajectory is slowly changed (see Figure 2 for an example). Choosing how the deflection is accomplished has significant geopolitical considerations and will likely require the cooperation of multiple nations. Finally, definitive knowledge that an impact will actually occur is often difficult to determine from ground-based measurements and the probability of impact will likely not be a certainty before a deflection mission is undertaken.

The gravity tractor is a planetary defense technique that uses the gravitational attraction between a rendezvous spacecraft and the NEO to gradually alter the trajectory of an impactor. With this approach, the spacecraft maintains separation from the NEO by using its thrusters to oppose the small gravitational attraction between the two bodies without pluming the NEO, which reduces the technique’s effectiveness. The gravity tractor requires the use of a low-thrust, high-efficiency propulsion system, such as Solar Electric Propulsion (SEP), to balance the gravitational force while minimizing the propellant required for the deflection. With this technique, the NEO is accelerated in a very uniform manner with only extremely small tidal forces causing any internal structural stresses. One of the shortcomings of the traditional gravity tractor approach is that the applied force is exceedingly small and depends on the mass of the spacecraft. This results in many years or decades of operation to alter the impactor’s trajectory and a decade or more of warning time.

• 

Introduction

The National Aeronautics and Space Administration (NASA) is currently developing a mission concept known as the Asteroid Redirect Mission (ARM), which includes the goal of robotically returning a multi-ton boulder (typically 2-4 meters in size) from a large Near-Earth Asteroid (NEA), 100 meters or greater in size, to cislunar space using an advanced 50 kW-class Solar Electric Propulsion (SEP) spacecraft designated the Asteroid Redirect Vehicle (ARV). After the ARV returns to a lunar distant retrograde orbit (LDRO) in the mid 2020’s, initial astronaut exploration and sampling of the returned material will take place as part of ARM. Subsequent human and robotic missions to the asteroidal material would also be facilitated by its return to cislunar space and would benefit scientific and partnership interests, expanding our knowledge of small celestial bodies and enabling the demonstration of mining of asteroid resources for commercial and exploration needs. The capabilities, systems, and operational experience developed and implemented by ARM and subsequent missions to the returned asteroidal material will advance NASA's goal of sending humans to deep-space destinations and eventually to surface of Mars. The robotic mission will also permit the demonstration of planetary defense techniques.

The robotic mission to capture a multi-ton boulder from the surface of a large NEA is depicted in Figure 3. The maximum boulder mass that can be returned is currently limited by the ARV xenon propellant capacity (~10 t) and the target asteroids available with orbits that allow returns in the mid-2020 time period. The maximum returnable mass is currently estimated to be approximately 40 metric tons. The capture system design has focused on retrieving a boulder that is 1-4 meters in size (up to a mass of ~70 t), but the design can be scaled to accommodate significantly larger boulders. This option includes the opportunity to demonstrate future planetary defense strategies on a hazardous-sized NEA. Inspired by the mission requirement to collect a boulder from the asteroid and thus dramatically augment the rendezvous spacecraft mass with in-situ material, the idea of the Enhanced Gravity Tractor (EGT) technique was conceived.

• 

EGT uses mass collected in-situ to augment the mass of the spacecraft, thereby greatly increasing the gravitational force between the objects. The collected material can be a single boulder, multiple boulders, regolith or a combination of different material types using a variety of collection techniques, including the use of a separable spacecraft to “harvest” the material. Since the material would not need to be returned to Earth for an actual deflection mission, significantly more mass could be collected to provide mass augmentation than can be achieved during the ARM robotic mission. The mass of the collected material for actual planetary defense effort would likely range from tens to many hundreds of metric tons based on the size of the impactor and warning time available. Depending on the SEP system’s capability (i.e., power, thrust, and propellant) and the mass collected, the EGT approach can reduce the deflection times by a factor of 10 to 50 or more over the standard gravity tractor method, thus reducing the deflection times of several decades to years or less. The ARM robotic mission will provide the first ever demonstration of the EGT technique on a hazardous-sized asteroid and validate one method of collecting in-situ mass.

Due to the collisional nature of how NEAs are created, the presence of retrievable material is a virtual certainty. Although the EGT does require some period of interaction with the target, the vast majority of the time is spent in the gravity tractoring mode, which is done without direct contact. This paper describes a simple, single spacecraft EGT methodology to explain the basic concept. There are many possible approaches and synergies that could significantly increase the effectiveness of the EGT that are available for further investigation. For example, the use of one or more separable spacecraft to collect and aggregate asteroidal material, along with an enhanced, higher power version of the ARV to act as the EGT “tug,” would greatly increase the effectiveness of the technique and provide additional mission robustness. Additionally, the efforts to extract and retrieve resources from large asteroids for future exploration and commercial mining efforts would greatly increase our capability to obtain the necessary mass for an EGT deflection effort against a future Earth impactor. Finally, the ability of multiple spacecraft to orbit the target in formation to provide the necessary velocity change can further reduce the time needed by the EGT technique to divert hazardous NEOs. These are just a few examples. Many other ideas, including combining EGT with other deflection techniques, are possible.

Concept of Operations

Once in the proximity of a hazardous NEO, the EGT operations consist of five phases: 1.) initial orbit determination; 2.) characterization; 3.) material collection; 4.) tractoring; and 5.) final orbit determination. Having a spacecraft near the asteroid allows for very precise orbit determination and confirmation that the threat is an impactor prior to any interaction with the asteroid. If an impact is confirmed, the spacecraft can facilitate a refinement of the ΔV required in order to avoid a direct impact or any gravitational keyhole passages [4] that could result in an Earth impact during a subsequent encounter. Orbit determination can begin hundreds of kilometers from the asteroid and continue throughout the characterization phase. The characterization phase will begin during the initial approach and provide a detailed gravity field, shape model, and imagery of the asteroid. The imagery will be used to identify boulders and other asteroidal material to be collected. Gravity and shape models will be used by the spacecraft’s guidance and navigation system during the collection phase.

Material collection operations will depend on the spacecraft capabilities, as well as the targeted material to be collected. Depending on the type of asteroid, pre-launch knowledge and imagery of the surface, the size of the asteroid, estimates of required ΔV, warning time, and the amount and type of material (single boulder, multiple boulders, regolith, etc.) can vary. While this paper will not discuss in detail all of the possible capture mechanisms and operations, it should be noted that it is desirable to have a robust collection capability to sufficiently augment the mass of the spacecraft.

• 

After collecting and securely restraining the asteroidal material, the spacecraft enters the tractoring phase. The EGT tractoring operations are similar to the standard gravity tractor with the spacecraft maintaining a constant distance (d) from the asteroid, countering the gravitational attraction by thrusting away from the asteroid with an equal force. Stationkeeping to maintain the desired orbit for any EGT method requires active navigation and awareness of the spacecraft’s relationship to the asteroid.

One way to achieve this standoff is having the spacecraft maintain a position along the asteroid’s orbital velocity vector. This in-line method, as shown in Figure 4, provides a simple navigation strategy with constant line of sight to the asteroid for range and position measurements. The thrust can then be adjusted to maintain the desired position. However, this method also requires canting of the thrusters in order to avoid pluming the asteroid. This requires additional propellant along with higher thrust to account for the cosine losses and thus increased power for electric propulsion (EP) system, or increased distance from the asteroid which would reduce the gravitational attraction and thus increase the deflection time.

Other methods have been proposed to increase the efficiency of tractoring. One of the most prominent is the spiral method. Figure 5 depicts this method in which the spacecraft enters a halo-like orbit around the asteroid’s velocity vector, creating a spiraling orbit when viewed in a sun-centered frame. This allows the spacecraft to decrease the distance (d) to the asteroid and increase the gravitational attraction while avoiding pluming the surface or requiring canting of the thrusters. By eliminating canting and setting the orbital period such that the centripetal acceleration counters the off-axis components of the gravitational force, the thrust required is equal to the net force along the velocity vector (v ⇀). This allows the full thrust capability of the spacecraft to be utilized in the deflection of the asteroid. The maximum deflection force is now a function of the mass that is collected and the minimum distance to the asteroid is set by risk posture, with thruster characteristics (e.g., plume angle, maximum cant angle, etc.) being a secondary consideration. While there are cosine losses introduced by the spacecraft not being aligned with the velocity vector because the resulting gravitational force is along the NEO-to-spacecraft line, these loses are overcome by the increased force as the spacecraft decreases the range to the asteroid which has inverse square relationship.

• 

Asteroid Redirect Mission EGT Demonstration

The ARM robotic mission would demonstrate the EGT spiral method and one method of collecting material from a hazardous-sized NEA. Due to the mission objective of returning the collected boulder to the Earth-Moon system, this mission will not have the time nor mass collection capability to impart a ΔV of the magnitude that would be required for an actual deflection mission. However, all phases of the EGT operations will be demonstrated, including producing a deflection which is large enough to measure either with the vehicle still in the asteroid’s vicinity or via groundbased radar measurements if possible.

Assuming the target asteroid hasn’t been visited by a precursor mission, which would provide shape and gravity models as well as detailed imagery, the ARV will spend approximately 14 days during initial approach to transition from a 1,000 km acquisition point to 100 km range. During this time, initial shape and gravity models will be developed and imagery will be gathered to begin identifying potential landing sites. Over approximately the next five weeks, a series of six fly-bys will be conducted with a close approach range of one km and relative velocities decreasing from a meter per second to approximately 0.1 m/s. The first four fly-bys are targeted over different latitudes to build a detailed gravity model and gather <10 cm resolution global imagery. A two week hold will be used to process the data and imagery and identify potential collection sites to be targeted during the final two fly-bys. A final two-week hold will then be used to identify and prioritize three collection sites. Three sites are chosen to protect against the unknowns of the surface and boulder characteristics. A total of five collection attempts and three dry-run sequences over different collection sites have been budgeted.

The collection process begins with a series of dry-runs that are used to test and demonstrate the navigation and control systems. The ARV will rely on optical Terrain Relative Navigation (TRN) that will track landmarks that are mapped during the fly-bys. The first dry-run will start at a range of 5 km and follow a passively safe trajectory to an altitude of ~200 m. During this dry-run, both the LIDAR and TRN systems will be able to develop solutions that will be tracked prior to the execution of a pre-planned maneuver at the end of the dry-run. Once the navigation system performance is demonstrated, the second dry-run will follow the same passively safe trajectory but then continue to descend down to an altitude of 50 m. At that altitude, the ARV will match spin rates with the asteroid and maintain a stationary position relative to the target boulder for 10 minutes to demonstrate the TRN filter and the control algorithms that will be required for the final descent.

The final descent will again follow the same passively safe trajectory down to 50 m altitude at which point the ARV will maintain a local vertical descent through touchdown. During the final 20 m, use of the thrusters that plume toward the surface will be limited to attitude control only with no vertical velocity control in order to minimize any disturbance to the surface. At touchdown, the residual velocity will be attenuated by the Capture and Restraint System (CRS). While on the surface, as depicted in Figure 6, the CRS will provide stability while a small downward thrust is maintained in order to increase the downward force in the extremely low-gravity environment. Two robotic arms with microspine grippers with anchoring drills [8] will then grasp the boulder prior to the CRS providing a mechanical push-off that will separate the boulder from the surface, breaking any cohesion, and provide an initial ascent without pluming the surface. Once the ARV and boulder are clear of the surface, a propulsive maneuver will be performed to achieve a slow drift from the asteroid while the boulder will then be secured and a series of small maneuvers will be performed to determine the mass properties of the combined boulder and ARV.

• 

With the boulder restrained and the mass properties updated, as depicted in Figure 7, the ARV begins to transit to an initial EGT spiral orbit. Much like the boulder collection dry-runs, prior to entering the final EGT orbit the ARV will demonstrate the EGT operations in an orbit with a range of one kilometer. This initial orbit will be held for about a week to demonstrate the TRN acquisition, control algorithms, and stationkeeping operations. The ARV will then transition to the final EGT orbit which will have a minimum altitude of one asteroid radius. During the EGT orbit, the ARV will track landmarks through the onboard TRN over two imaging arcs that occur just after crossing the terminator plane onto the illuminated side of the asteroid and just prior to crossing the terminator plane into eclipse. These imaging arcs will allow the system to precisely determine the ARV’s state and calculate any required updates to maintain the desired EGT orbit.

• 

This final orbit will be held for a pre-determined amount of time ranging from approximately 30-90 days depending on the target asteroid and collected boulder mass. This will provide a small deflection, limited by the propellant and time constraints of the ARM robotic mission, while not drastically altering the trajectory of the hazardous-sized target. The ARV will then maneuver to a stand-off location where it will wait an additional four to five months for the deflection to propagate. This will allow the asteroid to achieve advantageous Earth alignment for deflection verification, which will be accomplished using ground ranging to the ARV combined with precise ranging from the ARV to the asteroid. Once the deflection is verified to beyond a threesigma uncertainty, the ARV and captured boulder will begin the transit to back to the Earth-Moon system. Depending on the target asteroid’s future Earth approaches and tractoring time available, there may be the opportunity to observe the deflection using Earth-based radar, allowing the ARV to begin the return transit prior to verification.

Comparison of Traditional and Enhanced Gravity Tractor Techniques

Compared to standard gravity tractor operations, without augmenting the mass, the EGT is more effective, and thus, requires less time to achieve the same amount of deflection. Since the gravitational acceleration imparted on the asteroid is independent of the asteroid mass, a simple consideration would expect the benefit to be constant and equal to the ratio of the spacecraft mass to the mass of the spacecraft plus collected material up to the point that the gravitational force reaches that maximum thrust capability of the SEP system. However, Figures 8 and 9 show that the deflection time benefit provided by EGT over gravity tractor is not just a function of collected mass and SEP power available for thrusting, but also the asteroid size. This is a result of the characteristics of the propulsion system. Assuming a constant asteroid density, as the asteroid size increases the thrust required to counteract the gravitational attraction increases. This increase in required thrust is provided by increased mass flow through the propulsion system and therefore more propellant usage. Including this propellant and accompanying increased tankage in the mass of the spacecraft introduces an asteroid size dependency in the ratio of the EGT to the GT systems which produce the slopes seen in the figures.

As shown in Figure 8, almost 30 times less time is needed for a 200 m spherical asteroid (assuming a density of 2 g/cm3) with a 50 kW EGT system that has a 4,000 kg dry mass and 500 t of collected material. As the asteroid increases in size, the propellant required increases the mass of the GT at a proportionately higher rate than the EGT. This leads to the slow reduction in benefit seen. However, even at these lower power levels the EGT can reduce deflection times by one to two orders of magnitude for smaller asteroids, which are much more numerous and harder to target with kinetic impactor techniques because of their size. Figure 9 shows that using the EGT with a 300 kW SEP system and 500 t of collected mass provides almost a factor of 50 reduction in deflection time for a 300 m diameter asteroid. If the collected mass is reduced to 100 t, the EGT is still almost 10 times more efficient. As asteroids get larger, these numbers decrease, but even for a 500 m asteroid, the EGT method with 500 t of material can reduce the deflection time by a factor of approximately 15.

The impact of SEP power and thrust can easily be seen by comparing Figure 10 with Figure 11, which provide an estimate of the EGT deflection time (years) and propellant (metric tons of xenon) required for a given diameter asteroid. The gravitational force is proportional to the product of the asteroid mass and the combined mass of the spacecraft and collected material, and it is also equal to the thrust required to maintain the relative standoff position and thus impart the ΔV on the asteroid. As one or both of these masses increase to the point the gravitational attraction equals the maximum thrust capability of the spacecraft, the spacecraft then must move further away from asteroid to decrease the attraction to a point where it can be balanced by the thrust. This decreases the efficiency of the tractoring and provides a limit that can be seen as the lines converge. This also leads to the observation that for larger asteroids the EGT does not provide a benefit over the standard gravity tractor without additional thrust capability. This asteroid size is a function of the vehicle thrust. For a 50 kW system with a nominal dry mass of 4,000 kg that provides 1.63 N of thrust, this limit is reached with a 650 m diameter asteroid (assuming a density of 2 g/cm3). Keeping these assumptions while increasing the power to 300 kW and the thrust to 9.78 N, the limit is increased to over 1000 meters.

There are a few additional, and more subtle, aspects of this comparison. One is the minimum allowable range from the spacecraft to the asteroid. For the plots shown, a minimum range of one asteroid radius above the assumed spherical asteroid’s surface was maintained. When this range is combined with the assumed plume divergence half angle of 20 deg., the cosine losses of the gravitational attraction that are inherent to the halo orbit method are set and add another dependence on the asteroid’s radius. Another is the dependency of the SEP specific impulse (I_sp) on the throttle setting. This analysis assumed standard SEP throttle curves and a SEP system consisting of four thrusters that can produce a total 1.63 N. At maximum thrust, the SEP operates at maximum efficiency, however as the SEP is forced to operate at lower throttle settings, the I_sp decreases. As the asteroid size increases, more thrust is required and the SEP thrusters can be used closer to their optimal efficiency which leads to the dips seen in Figures 10 and 11, most notably in the standard GT time curves. While these variables do have some impact on the EGT effectiveness, they are much smaller than the overall thrust level of the spacecraft or the ability to collect more mass, which is seen by the dips almost disappearing once the EGT collects a mass of 50 metric tons or more.

• 

• 

It can be observed in Figures 10 and 11 that the amount of SEP propellant required for the EGT is relatively insensitive to the amount of mass collected. Expanded scales for asteroids up to 400 m are shown in Figures 12 and 13. Figure 12 shows that even a 50 kW EGT system can allow deflection times of less than a year for impactors up to ~175 m in diameter. The standard gravity tractor requires 18 years for a 100 m impactor (red line in upper left-hand corner). Figure 13 shows that the xenon propellant for the EGT is significantly lower than the standard gravity tractor, due to the EGT operating at a higher thrust and Isp. The current ARV with a maximum I_sp of 3,000 seconds and propellant capacity of 10 t would permit deflections of asteroids approaching 300 m depending on the amount of propellant needed to reach the target. Increasing the I_sp while still providing sufficient thrust levels would be needed to reduce the propellant loads required, which likely become prohibitive, along with deflection time for the larger asteroids with lower SEP power. Going to higher power SEP systems, which is the goal of future human exploration architectures, can increase the size of asteroid targets as shown in Figure 11. Finally, it should also be noted that the above analysis did not assume a specific orbit and therefore did not adjust the power and thrust available based on solar range. The power and thrust levels stated are the assumed power and thrust levels during the entirety of the EGT operations.

• 

• 

• 

• 

Mass Collection Options

From all the data collected over natural bodies greater than 100 m in size, such as natural moons and asteroids, there are an abundance of boulders and regolith littered on their surfaces. Hence designing a spacecraft that is capable of insitu mass collection is a natural choice for deflecting asteroids using the EGT method. The in-situ utilization of the native asteroid also has the obvious advantage of avoiding the launch and delivery to the asteroid of a spacecraft with the equivalent mass of the EGT.

Mass for an EGT deflection mission can be collected in the form of boulders, rocks, or regolith from the asteroid surface using a variety of options with the goal of collecting as much mass as needed to maximize the effectiveness of the technique and minimize operational complexity and risk. To achieve this, several collection options are conceptualized.

Concept 1 – Collecting a Single Boulder

In the ARM robotic mission concept, the capture system is being designed to capture a single coherent boulder with a maximum mass of 70 metric tons. The collection of a single boulder of this size and mass is adequate for a demonstration mission, but future planetary defense missions would benefit from being designed to capture a larger, more massive boulder in order to achieve the necessary deflection in a given warning time. The ARV capture system is scalable to larger boulders, with a boulder on the order of 10 meters in size required to provide approximately 1,000 metric tons of in-situ mass.

Concept 2 – Collecting Multiple Boulders

The second concept is a natural extension of the boulder collection functionality demonstrated by the ARM robotic mission — being capable of collecting multiple boulders. Since the boulders are scattered on the asteroid surface, the spacecraft still picks up one boulder at a time. During the characterization phase, the spacecraft surveys the asteroid surface and maps out the locations of the target boulders and the associated local terrains. A number of boulders are selected based on the estimated sizes and masses, and the sequence of collection is determined. During the collection phase, the spacecraft approaches and lands at the first boulder site, and after one boulder is secured proceeds to hop to the next boulder, and so on. In the micro-gravity environment in the vicinity of an asteroid, hopping between boulders is not expensive in terms of fuel consumption. For example, it takes as little as approximately 0.28 m/s of ΔV to escape the gravity well of asteroid 2008 EV₅, which is approximately 205 m in radius, and hopping on the surface takes far less ΔV than that. This concept is illustrated in Figure 14.

The single spacecraft design reduces mission complexity compared to concepts involving multiple spacecraft. However, there are significant challenges associated with this concept. First, the spacecraft has multiple capture mechanisms, and each of them has to function individually without interference. Depending on the size of the boulders, this can be challenging. Second, maintaining proper attitude to capture a boulder with other boulders without precisely known mass properties in tow is a challenging problem. Again, depending on the size of the boulders, the spacecraft may have to be tilted when approaching and capturing a different boulder, which may be limited physically because of the large solar arrays. Third, the Guidance, Navigation, and Control (GN&C) can be challenging. The dynamics associated with hopping combined with robotic capture mechanisms with large masses and the presence of large solar arrays are complicated. The sensor fields of view may become obscured by captured boulders, so additional maneuvers such as reorientations may need to be performed before approaching the subsequent boulders. Finally, significant portions of these operations will have to be performed autonomously due to the inherent communication delays.

• 

Concept 3 – Separable Collection Spacecraft and SEP Tug

The third concept attempts to address some of the challenges associated with using a single spacecraft to pick up multiple boulders by utilizing two spacecraft. The main SEP spacecraft, or “mother ship” does not go down to the asteroid’s surface. This spacecraft is designated as a SEP tug and remains in proximity to the asteroid. A smaller spacecraft is designed for the single purpose of collecting regolith or capturing boulders and ferries between the surface and the SEP tug and transfers the acquired material to the mother ship. The collection spacecraft can be equipped with a smaller capture mechanism and does not require the large solar arrays that are needed by the SEP tug to power the ion engines. Therefore, it can be smaller, less massive, and more maneuverable than a single spacecraft that must perform both the collection and tractoring functions. This concept is illustrated in Figure 15.

The SEP tug will need to station-keep at some acceptable distance from the asteroid and must have the capability to receive and store the regolith and/or boulders delivered by the collection spacecraft. The SEP tug can hover over the collection sites to provide accessibility for material transfer or it can hover over the polar region to minimize the propellant required for matching the rotation of the asteroid while hovering, provided that the asteroid is a single-axis rotator. After enough mass is collected, the SEP tug moves into position for EGT.

The smaller and specialized collection spacecraft greatly reduces the challenges associated with the surface operations, including maneuvering and collecting the asteroidal material. However, there are challenges with this concept, most of which lie in the GN&C aspects and repetitive automated rendezvous and docking (AR&D) required by the concept. The collection spacecraft has to dock with the SEP tug in order to transfer the material, and the SEP tug has to be able to receive and store the material in the micro-gravity environment. This requires that the two spacecraft must be controlled precisely so that no collision occurs and the material is successfully transferred to the SEP tug. Rather than just storing the collected material, this concept also introduces the possibility of processing asteroidal material to extract propellants, such as magnesium or sulfur, which could be used by the SEP tug during tractoring operations. This would be particularly valuable for larger asteroids that require several hundred tons of propellant to be delivered to the asteroid.

• 

The fourth concept deploys multiple collection spacecraft to collect asteroidal material and deliver it to the SEP tug. These collection spacecraft are likely smaller than the one envisioned in the second concept acquiring less mass during each collection operation. However, by having spacecraft scattered in a swarm fashion on the surface, this concept can access multiple areas simultaneously and can be more efficient in accumulating masses than a single collection spacecraft. In addition, having multiple collection spacecraft provides redundancy to ensure success of the mission. This concept faces the same GN&C and AR&D challenges as with the single collection spacecraft concept with the additional constraint of scheduling delivery of material to the SEP tug by multiple spacecraft. This concept is illustrated in Figure 16.

There are multiple variations and ways of implementing and combining these three basic concepts. Successful attempts to harvest asteroidal resources by NASA’s ARM and commercial entities (e.g., Planetary Resources, Deep Space Industries, and Kepler Energy and Space Engineering) will also have tremendous synergistic benefits for the successful implementation of material capture for a the EGT technique. Learning the basic techniques for mining material from larger NEAs will help improve the reliable operations needed to allow this approach to be successfully implemented for a future planetary defense effort.

• 

Other EGT Operational Concepts

This section briefly discusses several other EGT concepts of operations that are of interest. These concepts assume that a SEP system is still the primary source of thrust that facilitates the deflection of the asteroid. When using a SEP tug for EGT, it is very important the SEP thruster plume not impinge on the asteroid. This requires that the SEP engines are either canted or the EGT is offset radially from the asteroid velocity vector. As discussed previously, canting the SEP engine reduces the efficiency and the effectiveness of the EGT due to thruster cosine losses, and thrusters that minimize plume divergence greatly benefit all operational concepts. Offsetting the EGT using the spiral tractoring technique also introduces cosine losses of the gravitational pull in the along-track direction. The concepts discussed here aim to improve upon the existing EGT concepts in the literature by alleviating some of the aforementioned shortcomings, by utilizing solar sails and tethers.

Figure 17 shows the concept of attaching a solar sail to the EGT spacecraft. The Solar Radiation Pressure (SRP) naturally pushes the EGT away from the sun, and thus, offsetting the EGT from the asteroid velocity vector. The solar sail can also be tilted so that a force component can be generated in the along-track direction to supplement the tugging force. The position of the EGT relative to the asteroid is an equilibrium resulting from balancing three external forces, gravity, SEP thrust, and SRP. An appropriate equilibrium can be established by trading the combined spacecraft mass, the size of the solar sail, as well as the solar sail tilt, given the thruster plume divergence angle.

Using multiple EGTs in formation can drastically improve the efficiency of the asteroid deflection. For example, Wie showed that placing n spacecraft in a halo gravity tractor orbit is n times more efficient in deflecting an asteroid. However, this requires tight control of the spacecraft positions to prevent them from colliding with each other as well as the asteroid’s surface. This issue can be mitigated if the spacecraft can be naturally separated. Figure 18 illustrates such a concept, which is a view of a 3-EGT scenario from behind the asteroid in the along-track direction. It can be seen that each of the three EGTs is attached to a solar sail, and by tilting the solar sails about the along-track vector, the forces in the cross-track direction separate the spacecraft naturally. These EGT spacecraft do not fly in a halo orbit in front of the asteroid. Instead, they are naturally held at their respective equilibria due to balance of external forces.

• 

• 

The effectiveness of the EGT operations is greatly dependent on the gravity component in the along-track direction. Thus, it is preferable to keep the mass close to the asteroid. Figure 19 illustrates a concept that keeps the augmenting mass on a tether. The augmenting mass can be placed much closer to the asteroid to increase the gravitational pull, to the limit of the SEP thrust capability, with much less mass while the SEP tug can be placed further from the asteroid for increased safety margin. Similar to the approach shown in Figure 17, a solar sail is used to provide the radial offset, and it can be tilted to augment the tugging force. The dynamics associated with the tether in the micro-gravity environment can be complicated, and need to be carefully analyzed.

Figure 20 shows a concept where the EGT is in-line with the asteroid velocity vector. This concept requires the SEP engines to be canted to prevent the plume streams from impinging the asteroid surface. This reduces the effectiveness of the gravity tractor due to the cosine loss of the SEP thrust in the along-track direction. For example, Lu showed a concept where the effective thrust for tugging the gravity tractor is only half of the total available thrust due to canting the SEP engines 60 degrees from the along-track direction. The concept here aims to reduce the cosine loss. As shown in Figure 20, the augmenting mass is attached to a tether, and kept close to the asteroid, while the SEP tug is kept farther away in the in-track direction. Because of the increased distance from the asteroid to the SEP tug, the SEP engines do not need to be canted as much as in the case where the SEP tug is closer to the asteroid, assuming the thruster plume angle remains the same. Clearly, this concept increases the efficiency of the EGT operation. Here, the mass can be kept closer to the asteroid than the scenario where the spacecraft and the augmenting mass are collocated. Thus, the same effectiveness of EGT can be obtained with a smaller mass. The challenge of this concept lies in the complicated dynamics associated with tethers in the micro-gravity environment. The complexity of station-keeping the mass and the interaction between the mass and the SEP tug need to be carefully investigated.

• 

• 

It is postulated that most of the boulders and regolith on the surface of an asteroid may be deposited by impacts from other small bodies. For example, Küppers shows that the boulders on the surface of asteroid Lutetia are mostly concentrated around the central crater in Baetica region, as shown by the images taken by the OSIRIS camera onboard Rosetta. This is consistent with the simulated distribution of boulders ejected from that crater. It is also theorized in Thomas that Shoemaker crater is the source of most boulders on asteroid 433 Eros. Boulders can also be created by thermal stresses. A larger structure can be fractured by the larger temperature gradients caused by crossing the terminator plane repeatedly. If these theories are correct, it is likely that most boulders should be loosely resting on the surface, with the forces keeping them on the surface being only the low gravity and cohesion.

Selection of boulder sites depends on many factors, which include lighting, communication links, asteroid rotation, etc. Here we touch upon the comparison of the sites on various latitudes in facilitating the boulder extraction only. All asteroids rotate in some fashion, with some tumbling (e.g., Toutatis) and others rotating around a single axis (e.g., Itokawa, 2008 EV₅, and Bennu). For a tumbling asteroid, it is difficult to characterize the pros and cons of going to various sites on the surface. However, for the principal-axis rotators, it is evident for the few well observed asteroids such as Itokawa and Eros, many of the boulders congregate in the equatorial regions. This can be explained by the slow process in which the boulders shift to the equatorial regions due to the extremely small but persistent centripetal acceleration. Thus, the abundance of boulders makes the equatorial regions more favorable than others. In addition, the centripetal acceleration is the strongest at the equatorial regions, which can facilitate picking up boulders. For example, Figure 21 shows a comparison of the gravitational and centripetal accelerations at various latitudes on a fictitious spherical asteroid with a 250 m radius and a density of 2 g/cm³. The boulder is 20 metric tons, and the spacecraft is 9.7 metric tons (wet mass) at 20 m above the surface when capturing the boulder. It can be seen that if the asteroid rotates more rapidly than approximately once every 2.4 hours, in the equatorial regions, once the cohesion is broken, the spacecraft can fly away with the boulder naturally without the need for external forces due to the centripetal acceleration being greater than the gravitational acceleration (green and red curves). The benefit of the centripetal acceleration diminishes as the collection site moves up in latitude. If boulder to surface cohesion is low, which can be expected for a boulder resting on the surface, there are likely regions on the surface where collection operations could be greatly simplified.

• 

Operational Challenges of Mass Augmentation

One significant operational challenge of the EGT method involves collecting the augmentation mass at the NEO. However, analysis that has been performed for the ARM robotic concept to date and the commercial interest in asteroid mining indicates that collecting many tons of mass from the surface of an asteroid is feasible and further analysis and concept development is warranted. The concept of operations currently being considered would provide the first demonstration of mass collection of the magnitude needed to successfully conduct an EGT deflection. Other collection techniques such as electromagnets, large quantity regolith collection, multiple boulder collection systems, and others have been envisioned and require further study and development.

The ARM robotic segment concept assumes that capture operations occur while the collection site is illuminated by the sun due to the reliance on optical navigation sensors and the desire to keep the ARV from experiencing an eclipse due to power, thermal, and potential charging issues. This constraint combined with the reliance on optical navigation during descent and the desire to maintain a passively safe trajectory as long as possible, sets a spin rate limit for accessible asteroids at a little over 3 hours. However, if a mission were solely focused on planetary defense, different designs could easily be envisioned that would remove or limit the reliance on optical navigation and/or allow the spacecraft to operate through an eclipse period that would relax this spin rate limit.

Finally, another concern about the spin rate is the existence of collectable material at the target. On small, fast rotators, the centripetal acceleration can exceed the surface gravitational forces leading to shedding of surface material and forming a monolithic body without any available material to collect. As shown in Figure 22, very few large asteroids have been observed to be spinning at a rate above the rubble pile “speed limit” rotation period of approximately 2.3 hours. A low cohesive strength of only 25 Pa can explain this observation. This leads to the conclusion that the vast majority of the large asteroids have the capability to retain surface material, and that material is likely to be loosely bound to the parent asteroid and readily collectable, thus making EGT a credible deflection technique for hazardous-sized impactors.

• 

Applicability to Hypothetical Threat “ 2015 PDC”

We analyzed the ability of a 50-kW spacecraft like the ARV to deflect the 4^th IAA Planetary Defense Conference hypothetical asteroid “2015 PDC” using the enhanced gravity tractor technique. There are two major challenges in this scenario for a gravity tractor. First, assuming that launch or departure from the Earth-Moon system is not possible earlier than spring 2017 (about a year after final observations are made), the impact date of September 2022 defined in this scenario leaves only 5.5 years to reach the asteroid and impart enough impulse to deflect it. This would be challenging for any slow-push/pull approach. Second, the asteroid orbit aphelion of 2.65 AU limits the available sunlight during parts of the diversion to only about 15% of the 1 AU insolation. This severely limits the power available for any technique that utilizes the solar power. Nevertheless, we found that there are some plausible solutions in which an ARV-class EGT can deflect the hypothetical asteroid 2015 PDC in the available time.

The only physical characteristic of the asteroid known at time of launch is the absolute magnitude, H = 21.3 ±0.4 (assumed to be one-sigma uncertainties). Depending on the albedo and density of the asteroid, this could correspond to a spherical-equivalent diameter from less than 100 m to more than 500 m, and a mass from less than 1 million tons to more than 100 million tons. The asteroid is more likely to be in the lower third of this range unless it has both a very dark albedo and the error in H makes it brighter than nominally predicted. As a test case we defined an asteroid with H = 21.7 (i.e. +1), albedo = 0.3, and density of 2.5 g/cm³ corresponding to a stony asteroid with a mass of 1.7 million tons. This is smaller and less massive than the most likely values, but within a reasonable range. The spherical equivalent diameter would be 110 m, but we assumed a 2:1:1 ellipsoid of the same volume as the predicted sphere, with dimensions of ~87 x 87 x 175 m. This non-spherical assumption is important because it influences how close to the asteroid the spacecraft can be, and the gravitational force is proportional to the square of the separation distance. We applied a constraint that the spacecraft should remain at least 100 m beyond the maximum dimension of the asteroid to avoid collision, corresponding to a minimum spacecraft-to-asteroid radius of 187 m when not thrusting, and radius when thrusting of about 200 m using the halo orbit approach defined and described earlier in this paper. Dense asteroids can be easier to move than larger low-density asteroids of the same mass, and spherical asteroids are easier to move than elliptical ones, because the gravity tractor can orbit closer to the center of mass and generate more gravitational force.

The force that can be applied to the asteroid is potentially limited by two factors. First is the available thrust from the spacecraft, based on the available power and the capacity of the propulsion system. Second is the gravitational attraction between the asteroid and the spacecraft plus collected augmentation mass. In most cases we investigated, gravitational attraction was the limiting factor, so it is more effective to collect as much mass as possible from the asteroid, up to an assumed limit of 1000 metric tons. It should be noted that this mass is greater than the current ARM robotic boulder capture system design requirement, so a modified capture capability would be necessary. This produced a net tractor force of approximately 1.0 N using the following equation from [9] (McInnes, C. R., “Near Earth Object Orbit Modification Using Gravitational Coupling”, Journal of Guidance, Control and Dynamics, Vol. 30, No. 3, 2007, pp. 870-873.):

• F_N – Thrust required to remain in the halo, also the thrust that the spacecraft applies to the asteroid-ARV system.
• G – Gravitational constant
• M_ast – Mass of the asteroid
• m_sc – Mass of the spacecraft with any mass augmentation
• ρ – Radius of the halo orbit from the trajectory centerline
• z – Offset distance of the halo orbit from the center of mass of the asteroid

It is assumed that the ARV spacecraft departs the Earth-Moon system with a characteristic energy (C₃) of 2.0 km²/s². This can be achieved by a spacecraft orbiting in high Earth orbit using a lunar flyby, or by a direct launch from Earth to escape on NASA’s planned heavy-lift launch vehicle known as the Space Launch System (SLS). The transit to the asteroid, shown in Figure 23 in green, takes 1,000 days and has a single 40 day coast period (shown in purple), though 10% power margin and a duty cycle of 95% allow for additional thruster off periods. Upon arriving at the asteroid on March 12, 2020, a three month long period of reconnaissance and mass collection is allocated before beginning the EGT operations. By thrusting for the next 824 days, the ARV is capable of deflecting the asteroid from the subterranean 2,790 km Earth periapsis radius (i.e., an impact) to 6,930 km allowing for a miss of 560 km altitude from the surface. In Figure 24, the trajectory of the ARV while thrusting with the asteroid is shown in green and the trajectory of 2015 PDC after deflection and subsequent Earth close approach is shown in purple. Given the very narrow miss distance margin, this scenario defines the limit of what this 50 kW-class vehicle can accomplish with the warning time and impactor orbit provided in the scenario and highlights the fact that more warning time and better remote characterization of impactors are highly desirable, particularly for slow-push/pull techniques.

• 

• 

As mentioned, the variables that affect the deflection are the time allowed to deflect and the maximum thrust that can be applied. The SEP system aboard the ARV is capable of 1.63 N of thrust and could be augmented with additional thrusters to upgrade the system, which would allow for a potentially shortened thrusting duration to reach the asteroid. Additionally, either larger arrays or new cell technology could take the maximum power at one AU to a higher level than the assumed 50 kW capability. More array power would allow the thrusters to operate at the maximum allowed halo thrust when farther from the Sun and would also allow for a shortened thrusting duration to the asteroid. Either of these vehicle modifications coupled with earlier detection would allow the ARV to be applicable to larger NEAs.

Warning Time and Compatibility with other Planetary Defense Options

As shown previously, a significant advantage of the EGT is that it can drastically reduce the deflection time compared with the standard gravity tractor. Although sufficient warning time is needed as is the case with all slow-push/pull techniques, EGT is a viable option when the warning time is measured in years, and not decades as is needed for the standard gravity tractor approach utilizing only the mass of the spacecraft. Figure 25 shows the approximate regimes of primary applicability of the four types of planetary defense techniques: civil defense, kinetic impactor, the traditional gravity tractor, and a nuclear explosive device. The EGT technique can significantly overlap the regime of the kinetic impactor, especially if a SEP spacecraft like the ARV has been developed and operated or if it has actually been launched and can be expediently refueled in space.

• 

The pros and cons and the typical mission scenarios and constraints of classic techniques for planetary defense such as nuclear blast, kinetic impactor and gravity tractor have been well documented in literature, while the EGT is quite a new concept. It is also a very flexible tool in the hands of policymakers when they have to choose the reaction strategy. The simplest mission scenario for the EGT is that it is chosen as the primary reaction strategy as soon as the asteroid threat is discovered and sufficiently characterized: the spacecraft is launched, it collects mass from the asteroid, and performs the EGT deflection.

However, the EGT is also very much complementary to the kinetic impact and nuclear explosion techniques. Indeed, assuming that policymakers decide to implement a kinetic impact approach or opt to deliver a nuclear explosive device, if the primary mission does not perform with full success and is not completely successful in deflecting the impactor or leaves smaller parts of the original asteroid still with a risk of impacting the Earth, the EGT can provide trajectory corrections to the impactor or can collect mass from the smaller asteroid fragments and perform the EGT technique on them.

Additionally, in principle the EGT spacecraft can also provide in one single mission (one single spacecraft) the nuclear option. The spacecraft could also carry a nuclear explosive device and deploy it after collecting mass from the asteroid for subsequent policymakers will have to decide if the nuclear explosion option should be performed right away, or if the EGT can be performed first. If the nuclear explosion is taken as the first mitigation technique, the EGT can maneuver to safe distance while the explosion takes place, and then come back to check if the primary option worked properly, and perform corrections through the EGT technique on the main body and/or any smaller fragments that might still have a risk of impacting with the Earth.

It is likely that in the future there will be multiple ARV buses ready to launch and already operational in space, for example to deliver logistics supplies to astronauts in cislunar orbit, where the first ARV has placed the redirected asteroidal material, or to deliver cargo to the Mars neighborhood. Since the EGT technique builds on the ARV bus, the fact that there could be multiple ARV-derived buses available would make the EGT a ready to launch option. So ready that it might already be in space and simply be repurposed for its critical new mission of planetary defense. Finally, with the ability to be refueled, the ARV itself could be used as a kinetic impactor augmented by the mass collected during normal asteroid mining and processing operations.

Summary

The Enhanced Gravity Tractor technique is a novel, innovative variant of the traditional gravity tractor that can significantly reduce the deflection time required to be an effective planetary defense approach. Using mass collected in-situ, which would likely range from tens to hundreds of metric tons depending on the size of the impactor and warning time available, allows for significant augmentation of the tractoring mass and greatly increases the gravitational force between the objects.

NASA’s ARM robotic segment will provide the first ever demonstration of the EGT technique and validate collecting a multi-ton boulder in-situ. For an actual mission to deflect an Earth impactor, the collected material could be a single boulder, multiple boulders, regolith or a combination of different sources. There are many ideas for mass collection techniques and operational augmentations that can increase the effectiveness and reduce the operational risks associated with the EGT technique, and several have been highlighted in this paper. Depending on the impactor’s characteristics, the propulsion system’s capability and the mass collected, the EGT approach can reduce the deflection times by more than two orders of magnitude. Although the EGT still requires a significant warning time to reduce the required ΔV for the deflection, the ability to alter the trajectory more rapidly allows the EGT technique to be applicable to a greater range of impact threats. The ability for multiple spacecraft to orbit the impactor in formation can increase the ΔV than can be applied and further reduce the time needed by the EGT technique to divert hazardous NEOs.

Finally, the spacecraft necessary to successfully conduct an EGT deflection can also support other planetary defense techniques in a coordinated manner to maximize the successful deflection of a future Earth impactor. Advancements in SEP propulsion, autonomous vehicles, and robotic systems applicable to human and robotic exploration, commercial asteroid mining, and the used of space-based resources can synergistically help provide a robust defense against future Earth impacts.

(ed note: In John Lumpkin's Through Struggle, The Stars, he has the creation of an astromilitary the other way around. Initially none of the nations of Earth have a space presence, since there is no compelling reason to spend all that money on a space program when there are so many problems at home. The unexpected great asteroid strike of October 17, 2031 changed all that.)

The Rock — Common term for Southern Ocean asteroid strike that took place on Oct. 17, 2031. The asteroid, about 280 meters in diameter, came from below the plane of the Solar System and was undetected by the meager capabilities of the (mostly volunteer) orbit watch organizations at the time. It created vast tsunami that inundated the coastlines of western Australia, southeast Africa, and southern Asia. Fatalities were estimated at more than three million.

The event spurred Japan to develop a full-scale space program, initially aimed at preventing future potentially hazardous asteroids from striking Earth.

“Don’t tell me you’re busy?”

“Crushingly. Important?”

“No. I’ll be back later.”

The U.F.P. Justice hung in null-G, poised, as its burdened commander labored over the ship’s supercomputer terminal. Two hours ago, the call had come in: “Unauthorized asteroid deflection burn, Dec. -5.419°, R.A. 41.17°, class ξ asteroid 1999 RQ36 ‘Bennu’. Deflection Δv = 0.26±0.03 m/s.”

Small deflections make big changes. Even the emission of absorbed heat makes asteroids move unpredictably, unless their surfaces are mapped in detail. But with literally millions of asteroids, the Yarkovsky effect is not worth the bother.

But now someone has gone and moved one of them. A pretty big one, maybe half a kilometer on edge. That would probably utterly destroy one of Earth’s megacities, should it hit one.

Which means someone landed on it, did a thermographic survey, plotted its orbit to high precision, and then nudged it deliberately, in a particular direction, an exact amount.

So, the question–was it some unhinged terrorist bent on the obliteration of Los Angeles? Or a miner secretly moving a motherlode of priceless volatiles back to base?

In 51 years, he’d know for sure. For now, there’d be only guessing.

"If you guys just wanted to be left alone," said Murdoch, "why did you start the war? Why did you move Eros?"

"Ah, I see," said Vasily. "The propagandists have written your history books. We did not start the war."

"Like hell you didn't," said Murdoch. "Shifting Eros's orbit wasn't an act of war? It would have wiped us all out if it hit."

"Eros was an accident," said Vasily. "A few idiots who didn't double-check their math. We are not monsters, Murdoch. They never meant to aim the asteroid at the Pacific Ocean."

"Bad enough. And what's worse, you all banded up to protect Eros and make excuses for them, and when we asked you to help make sure it never happened again, you jerked us off."

"Your terms were impossible," said Vasily.

"Permits, Vasily," said Murdoch. "That's all we wanted. Is it that unreasonable? Each one of these rocks is a potential mass extinction event. Is filling out a form first that terrible?"

"Permits? No, they are not unreasonable," said Vasily. "An absolute veto for Earth over all orbital adjustments, no matter how minor or necessary? And the right to blow us out of the sky if we refused? No sovereign people would accept that."

"And war was worth that? It looks to me like that's what you ended up with anyway."

"Of course that's what we got," said Vasily. "You made us an offer we knew we would never accept, and then called it self-defense when you attacked us. It was imperialism. A smash-and-grab. You came, imposed yourselves on us, and forced us to mine your resources and buy the junk you made with it. You planned to do it for years, for decades. That's why you built your shining fleets. Do not try to tell me otherwise, good Murdoch. They had no purpose but to conquer us. Eros just gave you the excuse."

I thought I'd take the "spaceguard" idea one step further — if Earth has sufficient military power to punish the belters for any potentially dangerous orbit shift, they have the military power to rule the belters, period.

In the revised backstory, the asteroids were initially seeded by settlers when ships were too slow to make maintaining a military presence in the belt economical (the belters sent minerals to Earth in unmanned "slow boats" which were little more than chunks of ore with engines strapped on).

Then when the Zubrin drive was invented, the Great Powers suddenly had the means to extend their reach all over the Solar System, including the asteroid belt.

Vasily is largely right: Earth seized on a careless mistake as an excuse to conquer the asteroids and turn them into 19th century African colonies or Appalachia in Space — a place where poor local people dig out their natural resources at the behest of distant outsiders who "own" the land, get paid a pittance, and spend it on manufactured goods made by the same distant outsiders.

Asteroid 624 Hektor was actually two bodies, a contact binary which had originally been 370 kilometers long. The Belters who'd first settled it nudged the two rocks apart and now 624 Hektor A and 624 Hektor B orbited Sol about ten thousand kilometers from each other. A was slightly larger than B, 190 kilometers long, the largest body in the "Greek camp" Trojan asteroids which preceded Jupiter around the sun at the Sol-Jupiter L4, and served as the capital and main settlement of the grandiosely named Republic of Hellas. B, 180 kilometers long, was leased to the United Nations for use as a neutral port strategically located between the inner and outer system, conveniently close to Jupiter.

The Hellans or Hellenics or whatever they called themselves (Fitzthomas couldn't remember and didn't care that much anyway) didn't particularly like having what amounted to a fleet base for half a dozen inner system Great Powers ten k-klicks from their capital, but they liked it better than frigates like New Jersey and her Chinese, European, Russian, Indian, and Brazilian counterparts roving through the Trojans blowing up their stuff. The Great Powers, in turn, didn't like anybody who wasn't as attached to Earth as they were with their grubby rock-rat fingers on the "Go" buttons of potential mass extinction events, but they needed the metals and hydrocarbons and water locked up in the rocks, and it was a lot cheaper to pay Belters to dig them out than to do it themselves. And Belters may have been pests, but they were equal opportunity pests. The Americans, Chinese, Europeans, Russians, Indians and Brazilians didn't trust their fellow Terrans not to steal all that loot for themselves and gain an insurmountable strategic advantage given a chance, and they were probably right not to. Belters only cared if they got paid.

So Hellas (and its counterpart at L5, the Aeneian Confederation) got to keep their independence and make money, the Terrans got their resources and carte blanche to blow the holy living hell out of any rocks that started moving without a permit, and the UN given the unenviable task of administering the whole thing. And it could have been worse for the Hellenics. The Aeneians had to share their capital of 617 Patroclus with the UN, with two settlements on opposite ends of the asteroid and spies scuttling out of the woodwork every time an Aeneian sneezed.

• 

The High Guard was one of the few truly international organizations operating out of Earth, a multinational task force designed primarily to monitor the outer reaches of the solar system, track asteroids and comets that might one day be a threat to Earth, and to watch for nudgers. The Earth Confederation had grown out of an economic partnership between the old United States and a number of other nations, most of them former members of the British Commonwealth—Canada, the Bahamas, Australia, and New Zealand. Several non-Commonwealth states had joined later on— Mexico, Brazil, Japan, and the Russian Federation.

The High Guard, however, included ships from the Chinese Hegemony, the Indian States, and the European Union as well, which perhaps made that organization more representative of the entire Earth than the Earth Confederation itself.

The Earth Confederation had become more than an economic alliance in 2132, toward the end of the Second Sino-Western War. In 2129, a Chinese warship, the Xiang Yang Hong, had used nuclear munitions to nudge three small asteroids in Main Belt orbits into new trajectories that, three years later, had entered circumlunar space, falling toward Earth.

The Xiang Yang Hong had almost certainly been operating independently; Beijing later claimed the captain had gone rogue when he learned of the destruction of his home city of Fuzhou, and had carried out what was essentially a terrorist operation. His plan had been to devastate both the United States and the European Union by dropping all three asteroids into the Atlantic Ocean, causing devastating tsunamis that would wipe out the coastal cities on two continents. U.S. and European fleet elements had destroyed two of the three incoming two-kilometer rocks in what became known as the Battle of Wormwood—a reference to a biblical prophecy in the Book of Revelation that sounded eerily like an asteroid hitting the ocean. One rock—a piece of it, actually, had gotten through, falling into the Atlantic halfway between West Africa and Brazil.

The devastation had been incalculable. The loss of life, fortunately, had been less than it might have been, since most of the world's coastline cities were already slowly being evacuated in the face of steadily rising sea levels. Even so, an estimated half billion people had died, from West Africa to Spain, France, and England, to the slowly submerging cities of the U.S. East Coast, to the vanishing islands of the Caribbean, to the coastlines of Brazil and Argentina. The ancient term weapon of mass destruction had, with that single deadly blow, taken on a radically new and expanded meaning. Coming hard on the heels of the deaths of 1.5 billion people in the Blood Death pandemic, Wormwood's fall into the Atlantic had come close to ending technic civilization across much of the Earth.

The partial success of the American-EU fleet, however, had spurred further cooperation, and the rapid expansion of the automated High Guard project that had been in place for the previous century. Every space-faring nation on the planet—even the recently defeated Chinese Hegemony—had contributed ships and personnel to the newly expanded High Guard, with the sacred charge that never again would mountains fall from the sky. The Guard's motto was "A Shield Against the Sky." Its headquarters was located in neutral Switzerland, at Geneva.

Two centuries later, with the Sh'daar Ultimatum, the High Guard offered the teeming worlds and colonies of the inner solar system their best first line of defense against this new and still mysterious enemy. Their charter had been expanded; besides watching for nudgers—the ships of nation-states or terrorists attempting to push asteroids or comets into new and Earth-threatening orbits—they were tasked with patrolling the outer perimeter of the solar system, identifying incoming ships and, if they were hostile, engaging them.

The High Guard's oath, a solemn and sacred promise sworn before the souls of those who had died at the Battle of Wormwood, both in space and in the thunderous doom of the incoming tsunamis, offered the lives of the High Guard's men and women as a literal shield against any threat from the solar system's depths.

It was an immense task.. .one far too vast to be practical. The High Guard currently numbered about two hundred warships, most of them aging Marshall-class destroyers like the Gallagher, or the even older Jackson-class frigates. At any given time, at least half of those vessels were in port for refit, maintenance, and resupply. Typically, they deployed for nine months at a time, patrolling out beyond the orbit of Neptune, serving as backup to the half million remote probes in the forty-AU shell.

That arbitrary shell around Sol gave scale to what was lightly called "the vastness of space." The surface area of a sphere with a radius of 40 astronomical units was over 20,000 square Alls., .close to 450 quintillion square kilometers.

That worked out to one ship per four and a half quintillion square kilometers—an obvious impossibility. In fact, both patrols and remote sensors tended to be concentrated within about 30 degrees of the ecliptic, which cut down things a bit...but there was always the possibility that an enemy would sneak in from zenith or nadir, where tens of billions of kilometers separated one sentry from the next.

Thinly spread or not, in the thirty-seven years since the Sh'daar Ultimatum, not one alien vessel had approached Earth's solar system, and the general perception of the civilian population back home was that the war was far away, too far to be a threat.

According to the data flooding in through Gallagher's sensors, that illusion of security had just been ripped away. At least thirty Turusch warships had materialized almost seven hours ago, some six light hours out from the sun and 25 degrees above the ecliptic., .roughly in the same part of the sky as Arcturus and Eta Bootis. Exactly what they'd been doing since then was not clear; the ships weren't registering on long-range tracking, and no more data was coming through from Triton since that one, quick, burst transmission.

But Lederer could make a good guess. Confederation tactics called for launching a high-G fighter or near-c bombardment of the target immediately, so that local defenses were overwhelmed. It was possible that enemy near-c impactors were already approaching Earth.

• 

     Salazar leaned forward. She mimed tapping behind her ear, twice, then sliced her throat with a finger.
     "We're in the clear, Salazar. No deepers, no syncing. Also," Rivera waved her hand towards the ruins up the mountain, "This place is a bit creepy. And so are you."
     "Tell me how much time it will take to rebuild the facility."
     "You couldn't have asked directly? We have to play cloak-and-dagger games?"
     "I don't want outside interference."
     Rivera frowned, then tapped her chin for several moments. "It's going to take at least six months to find the right people, who can tell us if it can be rebuilt. A year, if you insist on keeping it a secret. Then they need to determine if it can be rebuilt at all, and how."
     "This is asinine. We are talking about a 150-year-old technology."
     "It's not that we're more advanced, but that our tech is different. We might need production facilities that were abandoned a century ago. Until we understand how the whole thing worked, all bets are off."
     "Still asinine."
     "Honestly, it would be faster to tear it all down and rebuild. It wouldn't be cheap, and might take a few years to complete under the best of circumstances. We'd need to design the replacement, first, of course."
     "No good. It's bad enough that someone might notice construction crews, but if the dome is gone, outsiders will notice. We might be able to mask a retrofit as renovations, but we must give them something."

     "Why do you care what outsiders think? Who'd come up here?"
     Salazar pulled out a soiled piece of folded paper, and handed it to Rivera.
     "There's a souvenir shop in La Serena that sells these genuine antique tourist guides. I understand they make sure the guides are genuine and antique, with a concrete mixer full of gravel and some watered-down coffee. But they copy from actual historical guides. Tourists buy them, sometimes fully aware they're being ripped off. But some of the guides include sites that were long abandoned."
     "So I can see. Is it possible for me to keep this? If this is based on authentic information, this might be useful for the reconstruction."
     "Certainly. But you see the risk. I scouted the area before you arrived. There have been people here recently. Slobs. No respect. We can't be too conspicuous."
     "I'm curious — why all the secrecy? I would have expected you to welcome the tourist trade."
     "Mars. That's why."
     "I don't get it."
     "Do you realize how dependent A União do Sul is on Martian data? Without their observations, we are cut off from the heavens."

     "That's a problem?"
     "Not today, but you pay attention to the news, no? La Fuente is projected to take control of the Senate next month."
     "And you really think they'll break off relations with Mars?"
     "Maybe not right away, maybe not totally. But they don't see the value of the data, and if they did, they wouldn't trust the data anyway."
     "And this changes anything, how?" Rivera stood, stretched, looked up the mountain.
     "La Fuente is of course wrong. We need to know about any asteroids that could potentially devastate A União."
     "We already know all the important threats to Earth."
     "We know them now. We can't guarantee that it will stay that way. More importantly — we can't guarantee Mars won't change the facts."
     "Altering the data, you mean?"
     "Or altering the system. If I were Mars and had to wage war against any nation on Earth, I'd start hurling rocks. A small asteroid would be tricky to aim, but not impossibly so; difficult to stop on short notice; and impossible to survive. Smart nukes may as well be firecrackers."

     Salazar paused. "We need to watch the skies, independently. As far as we know, it might be too late — there could be changes in place, already. But we can ward against any sudden changes if we watch carefully."
     "We can launch space telescopes. That would be cheaper still."
     "They could see the launch, and they could more easily knock it out of the sky and make it look like an accident."
     "They wouldn't know what it did."
     "They might not take the risk."
     "Doesn't the Comity have their own satellites? Can't we just access their telescopes?"
     "The current détente won't survive La Fuente. When that goes, so does any data-sharing scheme — which, I remind you, is already under heavy scrutiny. People would notice."
     "Stealing?"
     "An option, if I am honest, but not an option to rush to. We're trying to minimize diplomatic incidents. And, this is beside the point. You should worry less about what other avenues we've explored, and worry more about how to get that thing working again." Salazar pointed up the mountain.

     "Very well. I need a team to start the process. We'll do what we can, as quickly as we can. If we can salvage or recondition any of it, we will, and if we can't, we'll figure out how to replace it. No guarantees on anything, except our best efforts under these conditions."
     "Get back to me before bringing anyone on-board who might view this as pro- or anti-Fuente. This should be treated neutrally."
     "We'll be talking much, trust me. Everything these days is either pro- or anti-Fuente." Rivera shrugged. "Honestly? This is a tragedy. Of all the reasons to re-open this facility, fear should have never been among them. You'll find that experts largely agree. Including the ones we'll have to hire."
     "Will they refuse?"
     "Not the ones I'm considering, no. It's a chance to demonstrate their patriotism while serving science. You may find some dissenters in any community, but the opportunities here are immense beyond security concerns.
     "Very well. I'll trust you to weed out any potential troublemakers. This project is too important to risk."

     "Are we done, then? I'd like to go up and take a look around, myself."
     "Of course. Contact me in three days with an update. We can't afford delays." Salazar stood as a ground car stopped near the bench.
     Rivera waved. "We'll be in touch." She began the hike up the trail to the dome, browsing the tourist guide. "'Fully automated,' eh? Unless La Fuente outlaws deepers — God forbid — that part should be easy to emulate or outright improve.

     As she emerged in a clearing, she got her first glimpse at the the dome. There was a piece of truss jutting out, and a few velours missing. Then she saw the hole in the side of the building underneath. According to the brochure, it was the Vertical Platform Lift. That didn't bode well. It was awfully close to the main pier.
     Decades earlier, a group aligned with La Fuente de Luz destroyed this telescope, which once beheld the entire sky every night for years on end, as a symbolic attack on space-loving Oggs. Now, La Fuente has come to power. And they wanted her to rebuild what they blew up. It would soften their anti-science stance, and prepare a defense against enemies. It'd mean putting astronomers to work, and a chance to serve A União.
     It'd mean feeding into anti-Augment, Earth First rhetoric.
     Rivera was also pretty sure that saying no was not a serious option. Salazar was the kind of bureaucrat that treated everyone like a potential enemy until confirmed. And keeping a project of this scale, with this much symbolic power, a secret, was beyond her. She was no spy. She was an astronomer, for Christ's sake. What did Salazar want, a barrier with a polite note? A platoon? Several square kilometers of stealth fabric?

     She sighed. Public service mattered. Being the Science Advisor, mattered. The Interior Advisor's requests, mattered.
     She wasn't being asked to betray country or refuse science — on the contrary. This data will hopefully benefit all humanity, some day. And it could save lives.
     Rivera kicked a stone, then fumbled behind her ear. "Quincy, fetch a car, please?"
     It's the right thing, Rivera told herself on the ride home. It is. And it's inevitable. And it's a good thing. It is.

     Yet.

“Detain the operative,” Colonel Sansom had said in his message, sent to her over a confidential channel. Alonza had seen the woman’s file, stored under the name she was using. This was a matter Colonel Sansom should have handled himself, but he had left suddenly to go to an asteroid tracking station two days ago, to supervise repairs after a micrometeorite strike had damaged three telescopes, and would not get back to the Wheel for another thirty hours at least. A more easygoing officer might have sent la subordinate to the station, but not the obsessively conscientious Jonas Sansom. Tracking the orbits of asteroids that might threaten Earth was one of the most important duties of Guardians, perhaps the most important. Colonel Sansom would report to his superiors that he had seen to this task personally.

• 

Big, flat, polyhedrals, 3000-8000m on a side, 300-1000m deep, three to 15 big annie plants. Battleplates are named for the big craters -- the sorts of events they exist to prevent (or, truth be told, cause.)

Battleplates were originally designed to protect planets from the sorts of events that create the geographical features for which the Battleplates are named. The student of geology should only need to hear names like "Chicxulub" (ref), "Vredefort" (ref), and "El'gygytgyn" (ref) to know that we're talking about large rocks landing where rocks ought not land.

While it might seem like overkill to have close to a hundred giant ships like these in one planetary system, that's because once you've moved all of the naturally occurring rocks-o'-doom from dangerous orbits, you begin to worry about someone else sending one at your homeworld from an oblique angle, and at velocities more typically associated with charged particles or recklessly-piloted warships.

Should a relativistic rock the size of a house hit your planet, it will ruin your entire (day geologic epoch). Battleplates, with their swarms of long-range, hypernetted sensor drones, are insurance against that sort of event. And with their massively overpowered annie-plants, they're good for all kinds of things, including the odd spot of intimidation.

"Come here first. We'll do Lutetia, then you fly back and take care of the beanstalk. Tight timing, but it will work." Regulo was frowning. "Pity about the damned flight regulations. If they'd let me put a decent drive on some of the ships, I could halve your transit time. About a year ago I had Cornelia explore some financials for me. Did you know that half our resources are tied up all the time, just sitting and waiting for materials to get where we need them in the System? I'm not talking transportation costs, either. I'm talking about the effects of delays on budgets."

Rob shrugged. "I don't like the time it takes to travel around the System any better than you do, but we're stuck with it." Regulo was chewing on an old and familiar problem, and one where Rob could see little chance of changing the rules. His time would be better spent examining the changes they would need for the Spider.

"Trips out to the Belt aren't too bad if you have plenty of work to keep you busy," Rob went on. "You can't buck the laws of dynamics. Unless you can come up with a matter transmitter, we're stuck with transit times to match the drives. Your only other hope is the General Coordinators. Get them to change the laws on maximum permissible drive accelerations, and you'll be able to cut the transits."