UNOBTAINIUM: We can't build a physical example of it, but insofar as we can postulate that it can be built at all, the laws of physics say it would behave like thus and so. While Handwavium and Technobabble tell you what you CAN do, Unobtainium usually tells you what is NOT possible. Examples: gigawatt laser, antimatter weapons, ladderdown reactors.
HANDWAVIUM: It flat out violates laws of physics. We're waving our hands and saying pay no attention to the man behind the curtain. Examples: faster-than-light drive, time travel, reactionless drives.
Science fiction authors can make up handwavium on their own with no help from this website, it ain't that hard. As long as you are not scared of RocketCat and his dreaded Atomic Wedgie. Trying to keep it internally consistent enough so it does not turn around and bite you on the gluteus maximus, on the other hand, is quite difficult. There are some guidelines here.
And just to be complete, also remember the difference between Unobtainium and Unobtanium:
Unobtainium (with a 'i') is originally an engineering joke: a material that has all the proprieties needed, but either doesn't exist, is inaccessible or is too expensive. It has since then been adopted by science-fiction fans and critics to describe a material with fantastic properties that, while not forbidden by known science, does not seem to exist so far. This is a good way to take some liberties with known science and engineering while keeping the setting realistic, or at least believable.
Unobtanium (without the 'i'), to be found in vast quantities on planet Pandora and the reason the massive expenses of interstellar travel can see a return of investment, certainly qualify: a room-temperature superconductor with presumably massive power density, the figure of tens of millions of $ per kg (though inflation may give or take a few zeroes) is believable for present or near-future technology. Supplemental material hints as a grave energy crisis on Earth and unobtanium being used to build fusion reactors, which is indeed one of the obvious applications.
The popular conception of a black hole is that it sucks everything in, and nothing gets out. However, it is theoretically possible to extract energy from a black hole, for certain values of "from."
They are just the thing to make high acceleration gravitational catapults.
Due to their extreme conditions, black holes have a thousand and one uses. A pity there doesn't seem to be any closer that a few light-centuries.
And by the way, there appears to be no truth to the rumor that Russian astrophysicists use a different term, since "black hole" in the Russian language has a scatological meaning. It's an urban legend, I don't care what you read in Dragon's Egg.
This is sort of like a gravitational Slingshot, but turbo-charged.
In case it wasn't obvious, these are all ultra-high tech. The closest known black hole is about 3,000 light-years away, neutron stars and close orbit white dwarfs are not much closer (for practicality's sake you'll need a faster-than-light starship). And creating ultra-dense objects is a little beyond our ability.
Back in 1915 this crackpot named Albert Einstein was putting the finishing touches on his screwball theory of general relativity. Among other things it predicted that gravitational fields will bend the path of rays of light, due to gravity warping spacetime. Isaac Newton's theory of gravity also predicts that light will bend around a massive object, due to the equivalence principle. However, Einstein's theory predicted twice the curvature of the helpless ray of light. In particular it predicted that a ray grazing the Sun would be bent 1.75 arcseconds.
Aha! It's time for an Experimentum Crucis death match! Two theories enter, one theory leaves!
Now it is more or less impossible for an astronomer to observe the light from a distant star that grazes the Sun. Observations are impossible since the all-destroying fury of the Sun will either burn a hole in your eye or set the camera on fire. However, there was a total solar eclipse due in 29 May 1919. If the sun is blocked out, the stars can easily be observed and their visible positions measured. Then you can measure the curvature of the light rays and see which theory bites the dust.
British astronomers Frank Watson Dyson and Arthur Stanley Eddington organized an expedition to Brazil and another one to the West African island of Príncipe. The results were unambiguous: Newton is dead! Long live Einstein! This made front-page news in the major newspapers and made the theory of relativity world famous. Predictably the scientific community was more sour about this, and refused to be convinced until the next eclipse produce results that were even more unquestionable. But that is part of the necessary checks-and-balances of the scientific method.
The warping of spacetime is the principle behind gravitational lenses. Glass can bend light so you can make a lens out of it. Gravity can bend light so you can make a lens out of gravity as well.
In 1979 an Anglo-American team around Dennis Walsh, Robert Carswell and Ray Weyman discovered two quasars. There were two highly unusual features about these quasars:
- They were unbelievably close to each other, especially since there ain't no such critter as a binary quasar
- Their redshift and visible light spectrum were unbelievably similar
The team members look at each other, then simultaneously said "gravitational lens."
There was a galaxy (actually a galactic cluster) about midway between the quasar and us, whose gravity bent light rays from the quasar into a double image. One image is from light rays that traveled 8.7 billion light-years, the other is from light rays that traveled 8.7 billion plus 1.1 light-years. Astronomers know this because they spot patterns of changes in brightness of one quasar image which happen in the other image exactly 14 months later.
In 1998 astronomers found that gravity would not only lens the images of quasars, it would do the same thing to images of galaxies as well. Instead of dots, these lensed galactic images looked like galaxies bent into arcs or even entire rings. These are called Einstein–Chwolson rings. The distant galaxies with the bent images would probably be far too faint to be observed by existing telescopes, were it not for the gravitational lensing effect of the intervening galaxy.
In 1979 professor Von Eshleman had an idea. Why not use gravitational lensing to make a super-duper telescope? Galaxies are too far away to be used as aim-able telescope lenses, solar system planet gravitational fields are too weak. But what about the Sun's gravitational field?
All you have to do is station a camera at syzygy with the Sun and the astronomical object to be observed (so you have a straight line connecting the camera, the sun, and the astronomical object). Oh, and the camera has to be at the focal length distance from the Sun.
The good news is that in theory such a gravity camera would allow a seeing object that were ten kilometers in diameter on the surface of a planet 100 light years distant. That is dynamite resolution, since current telescopes cannot even see the blasted planets.
The bad news is that the solar focal length is 542 freaking astronomical units away from the Sun. For purposes of comparison, the planet Neptune is 30 AU from the sun, the outer edge of the Kuiper belt is 50 AU, and the inner edge of the Oort cloud is 20,000 AU. The other bad news is that to look at another astronomical object, you'll have to either position another camera (sending it on a 541 AU trip), or move the first camera to another place on the focal sphere (moving along a great circle route on a a 542 AU radius sphere, up to 3400 AUs)
Actually, some astronomers calculate that the interference of the Sun's corona will force the use of a focal point around 1,000 AU.
Von Eshleman proposed a space mission called FOCAL (Fast Outgoing Cyclopean Astronomical Lens). Sadly, every national space agency who examined the proposal started laughing hysterically when they saw the price tag.
If you want the specific details, you can learn more than you want to know in this paper.
SETI researchers conservatively concentrate on electromagnetic signals from alien civilizations: radio waves and laser beams. They've been listing since about 1960, but they ain't heard nothin' yet. With the arguable exception of the Wow!_signal.
Claudio Maccone wrote a paper on using the Solar focal point to increase the bit rate of interstellar radio communication. This is using the gravitational lens as a transmitter instead of as a telescope.
However, the genius Freeman Dyson opined "So the first rule of my game is: think of the biggest possible artificial activities with limits set only by the laws of physics and look for those". Inspired by Dyson, A.A. Jackson decided to think big.
In his paper, Dr. Jackson explores the possibility of interstellar communication using neutrinos instead of electromagnetic signals. Neutrinos laugh at interstellar gas that block radio and laser beams. You can't see stars on the far side of the Coalsack Nebula because it blocks electromagnetic light waves, even though the nebula is 10,000 times less dense than a good laboratory vacuum. That's how pathetic light waves are. But with neutrinos, if a beam of the slippery little devils was sent through one freaking light-year of solid lead it would only stop half of them. The rest of the neutrinos would just go sailing through the lead like it was nothing.
Therefore an advanced alien civilization might favor neutrinos for interstellar communication. Far less static than radio or laser beam.
And you can amplify your neutrino beam if you focus it with a gravitational lens. Though in this case you'd probably want to use a neutron star or a black hole, instead of a sun.
Using some mathematics that I do not pretend to understand (see paper) Dr. Jackson calculates that the neutrino beam would have a width of only two centimeters at a range of 10,000 light-years! Which is great for communicating with one of your interstellar colonies or another civlization who you were aware of. You just aim the neutrino beam at their planet.
But this is terrible if you are trying to broadcast a signal to galactic civilizations unknown to you. Like the one on Terra. You don't know where to aim the beam. There are a lot of two centimeter circles on the surface of a sphere 10,000 light-years in diameter. The chances of an unknown civilization being on the lucky spot and hit by the neutrino beam are about 10-21 (one chance in a sextillion).
The solution is to send more beams. Lots more beams. We're talking 1018 beams (a cool quintillion beams). Make that blasted neutron star look like a neutrino disco ball on steroids. If each beam generator was one meter in diameter, all 1018 would fit in various orbits of 1,000 kilometers radius from the center of the neutron star. Each would create a neutrino beam aimed at the neutron star, which would be gravitationally focused into a fine beam firing from the far side of the neutron star, missing the other beam generators and traveling into the galaxy with their SETI signal.
Now the civilization making this neutrino beacon is going to have to be at a Kardashev 2 level, but nobody said this would be easy. This is the page about unobtainium, y'know.
This is from The Halo Drive: Fuel-Free Relativistic Propulsion of Large Masses via Recycled Boomerang Photons. It is a very clever way of constructing a Dyson slingshot without requiring the spacecraft to approach the binary so closely that it risks spaghettification. It performs the gravitational slingshot remotely.
Of course it does require a sizable black hole moving at high velocity. Which should not be a surprise, since this is the page about unobtainium.
As with the Dyson slingshot, the energy used to accelerate the spacecraft is coming from the motion of the hypergravity object. It is just that you could use the blasted thing daily for ten-thousand years before the slowdown of the black hole became detectable.
The spacecraft starts at a reasonble distance from a moving black hole. It fires a beam of photons (laser beam) at the edge of the black hole. The beam skims the black hole's photon sphere, being bent by gravity into a path around the far side of the black hole. The beam breaks free of the opposite edge, and travels back to the spacecraft. What's more, the black hole's relative motion has given the beam a blue-shift. Translation: the beam's energy has been increased and the black hole's relative motion has been slowed by an undetectable microscopic amount. The black hole acts like a gravitational mirror.
The spacecraft loses energy when it emits the photon beam, and normally it gains back exactly the same energy when it reabsorbs the reflected beam. Except that the beam has been blue-shifted, so the spacecraft gains the blue shift energy. This is used to accelerate the spacecraft. The old energy is used to send another bit of photon beam to go harvest some more blueshift. Keep this up until the spacecraft is too far away from the black hole for the beam to reach.
The end result is the spacecraft has been accelerated to 133% (4/3rd) the black hole's velocity, using none of its own energy. As previously mentioned, all the energy is coming from the black hole, but it has energy to spare. The spacecraft does not get close enough to the black hole to be damaged by dangerous gravitational tides nor deadly radiation. The only thing that gets dangerously close is the beam of photons, and photons are much more durable than a spacecraft.
Once the spacecraft has accelerated to 100% of the black hole's velocity, the halo drive will not get any more blue-shift energy. But by that point, it will have gathered enough blue shift energy to eventually accelerate to 133% of the black hole's velocity.
When using a black hole binary to make a halo drive, the spacecraft will be accelerated best if it is moving in a direction along the plane of the binary orbit. To move out of the plane of the orbit the spacecraft will have to use onboard propellant and use up some of the blue-shift energy. Kipping said he has not run the numbers but thinks that a spacecraft could move up to 20° out of the binary orbit plane and still have a final acceleration of 100% of the black holes orbital velocity.
Also interesting is the fact this drive is not limited to low-mass spacecraft, such as solar sail. The spacecraft can be arbitrarily large. "Arbitraily" being defined as "much less mass than the black hole". In other words it could accelerate a spacecraft with the mass of Jupiter.
If you are lucky enough to find a black hole moving near relativistic velocity, then you can kick your ship to relativistic velocities as well. Then you'd really better have a relativistic black hole at the destination or you'll never slow down.
To be practical, you had better set up another black hole halo drive at the destination in order to decelerate to a halt. If your ship can brake to a stand-still using its internal propulsion, it can probably perform the initial acceleration unaided as well, In which case you don't need the blasted black holes in the first place.
It is not required, but the scheme works better with a pair of black holes orbiting each other in compact binary configuration. Especially at relativistic speeds. For details see the paper.
Predictably for this to work the photon beam has to be aimed incredibly precisely. The radius of a black hole is called the Schwarzschild radius (rs). For the photon beam to boomerang, it has to approach the black hole's center closer than 2rs (yes, I know theoretically the distance to a black hole's center is infinity, just roll with it, OK?). But if it approaches too close, 1.5rs, the beam will become trapped in orbit around the hole (the "photon sphere").
Bottom line, the typical boomarange distance is one skillinth of a whillimeter above 1.5rs
The paper points out that this effect can be used for other things besides accelerating spacecraft. Instead of using the energy for propulsion, store it and use it for some other useful purpose. It could also be used to manipulate a binary black hole into a desired configuration, using the halo drive like titanic optical tweezers.
This was a totally silly sci-fi idea that dates back to when I was a young man. The idea was since a pocket transistor radio could pick up music broadcasts from radio stations with no wires involved (wirelessly), perhaps it would be possible for an engine to pick up electricity broadcast from a power station with no wires involved. The technical term is Inductive Charging or Wireless power transfer.
Nikola Tesla found out the hard way the drawback to this little scheme. The lions share of the power radiates into the wild blue yonder and is wasted, since Tesla's attempt to channel the energy into standing waves around the entire globe was an utter failure. This means the inverse square law is your arch-enemy.
True, there was lots of work done in the 1960s on transmitting power with beams of microwaves aimed at rectennas (mostly for titanic orbital solar power stations getting their electrical power to customers on the ground). However, while this was wireless, it was not a "broadcast." It was a narrowcast beam, if the receiving rectenna wandered outside the beam the power would be cut off.
Broadcast power was officially confirmed to be a handwavium idea.
Until everything changed in 2006 when some geniuses at M.I.T. figured out how to use resonant coupling to transfer large amounts of power over a distance of a few times the resonator size. You sometimes see this used to charge smartphones, by laying the phone on a "charging mat". Admittedly, a distance of a few times the resonator size is a pretty pathetic range.
For now, broadcast power seems to have made the jump from pure handwavium into fringe unobtainium.
The main practical problem is how does the power company determine who tapped some power, so the company knows where to send the bill?
This is an ancient idea that is hard-core unobtainium. The idea is if you pick a spot on Terra, somehow dig from that spot to the core of the planet and continue until you emerge at the antipode, in some manner (left as an excercise for the reader) prevent the tunnel from imploding, you will have a gravitationally powered subway. Unobtainium, we can calculate exactly how it would operate, but there is no way we could make one.
The technical term is Gravity Train.
You can get a more precise view of a given tunnel's antipodes locations by using the online Antipodes Map. Though a cursor glance at the map above shows that most tunnels have both ends located in the ocean (white areas), and of the ones that involve dry land most have an oceanic end (gold and blue areas). Very frew location have both ends on dry land (orange areas).
Actually, the tunnel does not require the ends to be at the antipodes, it does not have to pass through the center of the planet. All straight-line tunnels (using only gravity as the propulsive force) take the same amount of time to transit, regardless of where the end points are. Transit time is faster if the tunnel is a hypocycloid curve between the points. Sadly if the two points are antipodes, the hypocycloid curve becomes a straight line. For the equations to calculate the transit time, go here.
There are a couple of theoretically possible ways to convert a sun into a rocket. A "stellar engine" as it were. The big advantage is that the sun will drag along its solar system with it, so you don't have to pack for a trip. The ultimate in mobile homes.
Why would any Kardashev type II civilization want to expend so much time and effort on such a thing? Well, there are a few obvious motives:
- A close by star is due to go supernova as it passes near enough to irradiate your entire solar system with deadly radiation. And it is inefficient to build zillions of starships to move your entire civilization.
- A close by star is due to go howling through your Oort cloud, and perturbing the orbits of literally trillions of comets. This will ensure that in a million years or so every single planet in your solar system is going to have the living snot beat out of it by a carpet bombing of cometary impacts.
- Your entire civilization is composed of rabid space tourists
- Your solar system is all mined out / has an elderly dying sun / dystopianly over-populated and for whatever reason you don't want to leave it via spaceships. So you move your system close to another solar system ripe with extensive virgin tracts of ore / fresh young sun / huge tracts of land. Jack Williamson used this in his novel The Legion of Space, home of the dreaded giant jellyfish-like Medusae who drive their solar system like a pirate rocketship to invade innocent planets.
- There is some Cosmic Menance threatening the galaxy, and the safest place to move your civilization is to another galaxy.
Please note that in our galaxy there are some real stars that are moving unusually fast. As far as astronomers can tell (or are willing to admit), all of these are naturally occuring.
Runaway stars are clipping along at around 100 kilometers per second. They are thought to be binary stars which passed too close to another star so one star got sling-shotted out. Or one star of a binary star system where the other blew up in a supernova.
A good example is Barnard's Star aka "Barnard's Runaway Star" or "Greyhound of the Skies". Astronomers measured the lateral speed and the radial velocity to calculate a space velocity of 142 km/s which is smokin'. And it is only 1.8 parsecs away (5.98 light-years), making it the fourth-closest star to the Sun.
Hypervelocity stars on the other hand are screaming along like the proverbial bat-outta-hell. They move at about 1,000 km/s, which is quite a bit more than the galaxy's escape velocity. They are thought to have been sling-shotted by the Sagittarius A* supermassive black hole at the center of the galaxy.
For science fictional purposes hypervelocity stars are stellar engine stars with the pedal to the metal, doing their best to get the heck outta Dodge ASAP. If the protagonists in your SF novel discovers such stars, the important plot question is: what do they know that we don't? Apparently there is some awful thing that terrifies that star's civilization enough so they are running away. Keeping in mind that civilization is powerful enough to thrust their entire solar system up to a thousand klicks a second, presumably whatever is scaring them is even more powerful.
This is a passive, minimalist stellar engine. It is basically a parabolic mirror with a slightly larger radius than the star.
The sunlight heading "aft" goes unimpeded. The sunlight heading fore is reflected by the mirror so it goes aft. The net result is an asymmetrical solar flux, which is the functional equivalent of a photon drive. The star is now a stellar engine, thrusting fore and dragging its solar system along for the ride. For a sunlike star the accelaration is only about 10-12 m/s2, but that ain't bad for moving an entire freaking solar system. True it can only deflect a sun by about 10 parsecs (32 light-years) in 250 million years (one galactic revolution), which is not fast enough to escape a supernova if the pre-nova forms in a region obscured to observation.
The mirror is held stationary with respect to the star with the star's gravitational attraction counteracted by the solar flux (i.e., the mirror is a statite)
Be sure the mirror is parabolic, not hemispherical. Parabolic will make a nice thrust beam. Hemispherical will just bounce all the sunlight back to the sun and make it go nova or something.
Safety tip: direct the sun beam at ninety degrees to the solar system's ecliptic to avoid inadvertently incinerating any of the planets.
This is from Stellar Engines: Design Considerations for Maximizing Acceleration (2019).
This is a much more active system than the Shkadov thruster. It takes lots of high tech engineering. But it can produce about three orders of magnitude more acceleration (one-thousand times more), around 10-9 m/s2. This can deflect a star by 10 parsecs (32.6 light-years) in as little as one million years. In five million years you can delta-V the sun by a whopping 200 km/s. That's runaway star territory.
This is strong enough to eventually make a sun orbit the galactic core retrograde, which is convenient for an expansionist civilization (maximizes the number of stellar fly-bys). It is also strong enough for a galactic escape trajectory, for civilizations who want to escape the cosmic horror that is consuming the galaxy.
The core of the Caplan system is a series of modified Bussard Ramjets. The front is a magnetic scoop tens of thousands of kilometers in diameter, funneling in the interstellar medium into a fusion rocket engine. Which is a problem for a starship, since the medium is a thin gruel of only 10-21 kg/m3.
Ah, but what if instead of the sparse interstellar medium you instead funneled in the more substantial solar wind from the sun? A zillion times more rich! Unfortunately it is only rich enough to acclerate the sun by 10-16 m/s2. Which is four orders of magnitude weaker than the simpler Shkadov thruster, so what's the point?
Not good enough? Why stop there? Surround the sun with a partial Dyson swarm of solar mirrors. Focus the sun's rays on a few spots and boil that solar material into titanic plumes of thick ramjet fuel. A zillion-zillion times more rich. Now we're talkin'. Acceleration of 10-9 m/s2, eat that Shkadov!
The ramjets gulp the billions of tons of fuel and burns them in huge fusion reactors. The exhaust is emitted in two jets: one away from the sun for acceleration, the other towards the sun to keep the blasted ramjet from colliding with it. The sunward pointing exhaust transfers exhaust momentum to the sun. The ramjets essentially become tugboats pushing the sun.
Dating back to the Orichalcum that was all the rage in Atlantis, to modern-day Wolverine's indestructable Adamantium bones, fiction is full of marvelous materials that would be oh so useful if we could only lay our hands on some.
- Made of Indestructium: object is made of a material that renders it almost impossible to destroy. Useful to make into armor. Examples: Adamantium, Vibranium, Inoson, Lux & Relux, General Products hulls, Phrik, Sauron's One Ring, Stephanie Plum's Uncle Sandor's '53 powder blue Buick.
- Made of Incendium: object is made of a material that will burst into flames at the merest touch of a spark, and burns furiously for an indefinite time. Examples: General Grievous' few remaining organic parts, Vampires in the Twilight movies, Wights from Game of Thrones.
- Made of Explodium: object is made of a material that violently explodes with multicolored pyrotechnics if it is ever so slightly damaged. Examples: hydrauic fluid in Armoded Trooper VOTOMS, the atmosphere of the planet Psychlo, the Ford Pinto in the movie Top Secret!, control panels on the bridge of the Starship Enterprise, everything in a Michael Bay movie.
- Phlebotinum: object is made of a material that can cause any weird effect the author requires for their novel. AKA pure Handwavium.
You may have noticed that there are a few chemical high explosives that contain nitrogen in their molecular structure, e.g., nitroglycerin, TNT, HMX, PETN, nitrocellulose. This explosive energy comes from nitrogen's triple bond.
In the science fiction spirit of making space opera by turning the volume up to eleven, authors have postulated chemical explosives that rival nuclear devices by containing outrageous amounts of nitrogen.
Recently in the real world Dr. Mikhail Eremets of the Max Planck institute for chemistry manage to actually synthesize polymetric nitrogen aka a "nitrogen diamond" (pdf report here). On the minus side the stuff is only stable in a diamond-anvil cell under a pressure of 1.1×106 freaking atmospheres. On the plus side detonating it will release five times the energy of the most powerful explosives, greater than all known non-nuclear substances (33 kiloJoules per gram, TNT is about 4.2 kJ/g).
Before the nitrogen diamond, the worst known nitrogen explosive was 1‐diazidocarbamoyl‐5‐azidotetrazole. This insanely dangerous molecule contains no less than fourteen nitrogen atoms. It's heat of formation is a frightening 357 kcal/mole. It has its very own entry in Derek Lowe's infamous list of Things I Won’t Work With. Even its infrared spectrum is unknown, because as soon as they shined a dim IR lamp on the compound it promply exploded.
Dr. Winterberg wishes to utilize deuterium fusion for propulsion. Due to limitations he rejects magnetic confinement and conventional inertial confinement. Using fusion bombs in an Orion pulse engine was rejected because fusion bombs do not scale down well. Below a certain point the fission explosives used to ignite the fusion reaction cannot efficiently burn all the fission fuel, leading to a waste of expensive plutonium and widespread fallout.
Instead, Dr. Winterberg proposes metastable chemical explosives powerful enough to ignite a fusion reaction. Cheaper than a fission physics package, no expensive plutonium needed, and no radioactive fallout of fission fragments and unburnt plutonium.
|Specific Impulse||1,700 sec|
|Exhaust Velocity||16,700 m/s|
Most of the data here is from Metallic Hydrogen: The Most Powerful Rocket Fuel Yet to Exist by Isaac F. Silvera and John W. Cole.
Hydrogen (H2) subjected to enough pressure to turn it into metal (mH), then contained under such pressure. Release the pressure and out comes all the stored energy that was required to compress it in the first place.
It will require storage that can handle millions of atmospheres worth of pressure. The mass of the storage unit might be enough to negate the advantage of the high exhaust velocity.
Or maybe not. The hope is that somebody might figure out how to compress the stuff into metal, then somehow release the pressure and have it stay metallic. In Properties of Metallic Hydrogen under Pressure the researchers showed that hydrogen would be a metastable metal with a potential barrier of ~1 eV. That is, if the pressure on metallic hydrogen were relaxed, it would still remain in the metallic phase, just as diamond is a metastable phase of carbon. This will make it a powerful rocket fuel, as well as a candidate material for the construction of Thor's Hammer.
Then that spoil-sport E. E. Salpeter wrote in "Evaporation of Cold Metallic Hydrogen" a prediction that quantum tunneling might make the stuff explode with no warning. Since nobody has managed to make metallic hydrogen they cannot test it to find the answer.
Silvera and Cole figure that metallic hydrogen is stable, to use it as rocket fuel you just have to heat it to about 1,000 K and it
explodes recombines into hot molecular hydrogen.
Recombination of hydrogen from the metallic state would release a whopping 216 megajoules per kilogram. TNT only releases 4.2 megajoules per kg. Hydrogen/oxygen combustion in the Space Shuttle main engine releases 10 megajoules/kg. This would give metallic hydrogen an astronomical specific impulse (Isp) of 1,700 seconds. The shuttle only had 460 seconds, NERVA had 800, and the pebble bed NTR had 1,000 seconds. Yes, this means metallic hydrogen has more specific impulse than a freaking solid-core nuclear thermal rocket.
Isp of 1,700 seconds is big enough to build a single-stage-to-orbit heavy lift vehicle, which is the holy grail of boosters.
The cherry on top of the sundae is that metallic hydrogen is about ten times more dense (700 kg/m3) than that pesky liquid hydrogen (70.8 kg/m3). The high density is a plus, since liquid hydrogen's annoyingly low density causes all sorts of problems. Metallic hydrogen also probably does not need to be cryogenically cooled, unlike liquid hydrogen. Cryogenic cooling equipment cuts into your payload mass.
The drawback is the metallic hydrogen reaction chamber will reach a blazing temperature of at least 6,000 K. By way of comparison the temperatures in the Space Shuttle main engine combustion chamber can reach 3,570 K, which is about the limit of the state-of-the-art of preventing your engine from evaporating.
It is possible to lower the combustion chamber temperature by injecting cold propellant like water or liquid hydrogen. The good part is you can lower the temperature to 3,570 K so the engine doesn't melt. The bad part is this lowers the specific impulse (nothing comes free in this world). But even with a lowered specific impulse the stuff is still revolutionary.
At 100 atmospheres of pressure in the combustion chamber it will be an Isp of 1,700 sec with a temperature of 7,000 K. At 40 atmospheres the temperature will be 6,700 K, still way to high.
Injecting enough water propellant to bring the temperature down to 3,500 to 3,800 K will lower the Isp to 460 to 540 seconds. Doing the same with liquid hydrogen will lower the Isp to 1,030 to 1,120 seconds.
The main drawback to inertial confinement fusion engines is since beams of light do not push very hard, you need metric-assloads of laser energy to crush the fuel pellet to fusion ignition. Which requires lots of heavy lasers, savagely cutting into your payload mass budget. Since the laser pulse has to be microscopically short, the lasers have to be powered by huge banks of weighty capacitors, further slashing your payload budget.
Ultra-dense deuterium (UDD) is an exotic form of metallic hydrogen called Rydberg matter. As you can probably figure out from the name the stuff is dense. Real dense. As in 1028 to 1029 grams per cubic centimeter dense. About a million times denser than frozen deuterium.
For our purposes the interesting point is it is about 150 times as dense as your average pellet of fusion fuel when laser-compressed to peak compression. Yes, this means do you not need metric-assloads of laser energy to crush the fuel pellet, a pellet just sitting on the table is already at 150 times the needed compression. It is pre-compressed. All you need is a miniscule 3 kilojoules worth of laser energy to ignite the stuff. That is pocket-change compared to what 200-odd compression lasers require. In fact it is so little that a single laser can handle the job. This results in a vast savings on laser mass and capacitor mass.
The laser pulse has to be quick, so the power rating is a scary 1 petawatt. But by the same token since the pulse is quick, it only require the aforesaid 3 kilojoules of energy.
Since you do not have to compress the fuel you can avoid all sorts of inconvienient hydrodynamic instabilities and plasma-laser interation problems.
You also have virtually unlimited "fusion gain". Meaning that with a conventional IC fusion engine there is a maximum fuel pellet size due to the hydrodynamic instabilities and the geometric increase in compression laser power. With UDD you can make the fuel pellet as large as you want (well, as large as the engine can handle without blowing up at any rate). With other laser intertial confinement fusion, if you make the pellets larger, you have to make the laser array larger as well. Not so with the UDD drive. The fusion gain depends solely on the size of the pellet, you do not have to make the lasers bigger.
An important safety tip: since UDD has such absurdly low ignition energy, there is a statistical change a large number of UDD atoms would undergo fusion spontaneously. This dangerous instability means the spacecraft will carry ordinary deuterium fuel and only convert it into UDD immediatly before use.
The cherry on top of the sundae is UDD fusion does not produce deadly neutron radiation. Instead it produces charged muons, which are not only easier to deal with, but also can be directly converted into electricity. Left alone, the muons quickly decay into ordinary electrons and similar particles.
And since deuterium is plentiful in ordinary seawater, you do not have to go strip mining Lunar regolith or set up atmospheric scoop operations around Jupiter were you to use a fusion reaction requiring Helium-3.
Sounds too good to be true, I hear you say. Well, there are a couple of drawbacks.
The minor drawback is that D-D fusion has a specific impulse (and exhaust velocity) which is about half of what you can get out of D-T fusion or D-He3 fusion. This drastically increases the mass ratio required for a given mission delta-V. Having said that it is still much better than what you'll get out of chemical or fission engines.
But the major drawback is UDD might not even have that magic ultra-density.
You see, the vast majority of the UDD-related papers has been published by a single scientific group at University of Gothenburg, Sweden, led by Dr. L. Holmlid. Currently there are no third-party confirmations about UDD observations and generally very few discussions about it in the scientific community. Until the density figure is confirmed, it might be all a pipe-dream.
Material composed of nothing but closely packed neutrons. Found in the core of neutron stars. The best figure I can find for the density of neutronium is 4×1017 kilograms per cubic meter, and dwarf star matter 1×109 kilograms per cubic meter.
No, you can't us it as the ultimate armor because if you somehow take a chunk out of the neutron star's core, the accurséd chunk explodes.
Outside of the core the neutrons undergo beta-decay with a half-life of 10 minutes and 11 seconds (611 seconds) with each cubic centimeter emitting energy at a rate of 19 megawatts average over the first half life.
Translation: sitting next to a cube of neutronium will be like having four and a half sticks of TNT blow up in your lap every second for 611 seconds.
As with all half-life decays, the second half-life will only have half the energy (two and a quarter sticks TNT per second) but by that point there won't be much left of your miserable carcass anyway.
Physicist Luke Campbell points out to me that my understanding is imperfect. Beta-decay is the least of your worries. He told me "An additional thing I didn't see mentioned in the section on neutronium is that all the neutrons are unbound. That means, there is nothing sticking them together. Once removed from the crushing gravity of a neutron star, all the individual neutrons fly off on their own independent happy trajectories. In an instant, you no longer have any kind of -ium any more, but rather a flash of highly penetrating energetic ionizing radiation."
In atomic nuclei, neutrons and protons stick together due to the strong nuclear force. Since the neutrons in a neutron star are not in a nucleus, there ain't no strong nuclear force gluing them. They are unbound.
The only thing keeping them together is the neutron star's outrageous gravity field. Once you take a chunk of neutronium away from the neutron star's gravity, the unbound neutrons composing the chunk instantly go flying in all direction at relativistic speeds. In other words it becomes a blast of neutron radiation with a flux strong enough to shred you into subatomic particles.
Higgsinium may or may not be handwavium. It depends upon a subatomic particle called the negative Higgsino predicted by supersymmetry theory. So far there is no evidence for supersymmetry from any physics experiment, and obviously no proof the negative Higgsino exists.
Monopolium may or may not be handwavium. It depends upon a subatomic particle called a magnetic monopole. There have been a couple of experiments which produced candidate events that were initially interpreted as monopoles, but are now regarded as inconclusive. On the other hand, pretty much all of the various theories of subatomic physics predict the existence of monopoles.
The idea is attributed to Richard Feynman and it was popularized by K. Eric Drexler. It didn't take long before military researchers and science fiction writers started to speculate about weaponizing the stuff. A good science fiction novel on the subject is Wil McCarthy's Bloom.
There are many ways nanotechnology could do awful things to a military target. One of the first hypothetical applications of nanotechnology was in the manufacturing field. Molecular robots would break down chunks of various raw materials and assemble something (like, say, an aircraft), atom by atom. Naturally this could be dangerous if the nanobots landed on something besides raw materials (like, say, an enemy aircraft). However, since they are doing this atom by atom, it would take thousands of years for some nanobots to construct something (and the same thousands of years to deconstruct the source of raw materials).
But using nanobots for manufacturing suddenly becomes scary indeed if you make the little monsters into self-replicating machines (AKA a "Von Neumann universal constructor") in an attempt to reduce the thousands of years to something more reasonable. Suddenly you are facing the horror of wildfire plague spreading with the power of exponential growth. This could happen by accident, with a mutation in the nanobots causing them to devour everything in sight. Drexler called this the dreaded "gray goo" scenario. Or it could happen on purpose, weaponizing the nanobots.
Drexler is now of the opinion that nanobots for manufacturing can be done without risking gray goo. And Robert A. Freitas Jr. did some analysis that suggest that even if some nanotech started creating gray goo, it would be detectable early enough for countermeasures to deal with the problem.
What about nanobot gray goo weapons? Anthony Jackson thinks that free nanotech that operates on a time frame that's tactically relevant is in the realm of cinema, not science. And in any event, nanobots will likely be shattered by impacting the target at relative velocities higher than 3 km/s, which makes delivery very difficult. Rick Robinson is of the opinion that once you take into account the slow rate of gray goo production and the fragility of the nanobots, it would be more cost effective to just smash the target with an inert projectile. Jason Patten agrees that nanobots will be slow, due to the fact that they will not be very heat tolerant (a robot made out of only a few molecules will be shaken into bits by mild amounts of heat), and dissipating the heat energy of tearing down and rebuilding on the atomic level will be quite difficult if the heat is generated too fast.
Other weaponized applications of nanotechnology will probably be antipersonnel, not antispacecraft. They will probably take the form of incredibly deadly chemical weapons, or artificial diseases.
Some terminology: according to Chris Phoenix, "paste" is non-replicating nano-assemblers while "goo" is replicating nano-assemblers. Paste is safe, but is slow acting and limited to the number of nano-assemblers present. Goo is dangerous, but is fast acting and potentially unlimited in numbers.
"Gray or Grey goo" is accidentally created destructive nano-assemblers. "Red goo" is deliberately created destructive nano-assemblers. "Khaki goo" is military weaponized red goo. "Blue goo" is composed of "police" nanobots, it combats destructive type goos. "Green goo" is a type of red goo which controls human population growth, generally by sterilizing people. "LOR goo" (Lake Ocean River) nano-assemblers designed to remove pollution and harvest valuable elements from water, it could mutate into golden goo. "Golden goo" are out-of-control nanobots which were designed to extract gold from seawater but won't stop (the "Sorcerer's Apprentice" scenario). "Pink goo" is a humorous reference to human beings.
ACE Paste (Atmospheric Carbon Extractor) designed to absorb excess greenhouse gasses and covert them into diamonds or something useful. Garden Paste is a "utility fog" of various nanobots which helps your garden grow (manages soil density and composition for each plant type, controls insects, creates shade, store sunlight for overcast days, etc.) LOR paste: paste version of LOR goo. Medic Paste is a paste of nanobots that heals wounds, assists in diagnosis, and does medical telemetry to monitor the patient's health.
Computronium is a material hypothesized by Norman Margolus and Tommaso Toffoli of the Massachusetts Institute of Technology to be used as "programmable matter," a substrate for computer modeling of virtually any real object. It also refers to a theoretical arrangement of matter that is the best possible form of computing device for that amount of matter.
Superconductors are nifty wires that have exactly zero resistance to the flow of electricity. They are vital to the construction of ultra-powerful magnets (for coilguns, particle beam weapons, and some propulsion systems) and for hyperfast computers.
The first superconductors had to be cooled with expensive and troublesome liquid helium. They became practical when new superconductors were discovered which could work with cheap and easy liquid nitrogen.
But the holy grail is a superconductor that doesn't need to be cooled at all. These are high-temperature superconductors, colloquially called "room-temperature superconductors."
Larry Niven used superconductors a lot in his Known Space series, especially Ringworld. His electrical superconductors are also superconductors of heat, in accordance with the Wiedemann–Franz law. But in 2017 researchers at Berkeley Labs discovered an exception to the law. While all other known electrical conductors also conduct heat, the material vanadium dioxide does not. Unsurprisingly the stuff has other wierd properties.
This is an unnaturally strong thread one molecule thick. This means it has remarkably low mass per towing capacity, which makes it popular for moving asteroids and for waterskiing spacecraft and starships.
It will basically cut through anything except another molecule chain. Naturally it is also used to make edged weapons.