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Antimatter Propulsion [pdf]
- master_crab 3y agoAssuming it costs $10mil per mg in a highly efficient production scenario and you need 10^9 grams for “fast” interstellar travel means this probably isn’t doable. I guess there’s just no getting around fact that an antimatter reaction that creates 9x10^10 MJ/kg requires more robust electrical generation capabilities than we currently have (I.e fusion)
- actionfromafar 3y agoOr leveraging solar on a truly interplanetary scale. Could start by covering the Moon in solar panels.
- sheepscreek 3y agoIt would probably be (comparably) cheaper to trap anti-matter in space and bottle it up - essentially mining it.
- Torkel 3y agoAluminium was once more costly than gold or platinum, and bars of aluminium were exhibited alongside the French crown jewels at the Exposition Universelle of 1855. The fact that something is ludicrously expensive today when manufactured in ultra-small quantities says nothing about the cost if humanity goes all in on mass producing it.
- EA-3167 3y agoA different process for extracting metal from ore is hardly a new idea, it just took implementing the technology for bauxite. Producing antimatter without spending a ton of energy doing it is much more baked into the fundamental nature of the physics we understand today, and which has been very well tested. We already know what produces antimatter, and in ultra-lay terms it's "Pack so much energy into such a small space that pair production occurs." The only really conceivable shortcut for antimatter would be the discovery of large quantities of it somewhere close enough for us to essentially mine it. We've looked for the gamma signature of matter-antimatter annihilation in space, and we don't see it anywhere. So it isn't IMPOSSIBLE for antimatter to become affordable, but it's extraordinarily unlikely. If we want some sort of superior rocket, it's probably going to have to involve either some unforeseen tech, or our ability to spend planetary energy budgets on rocket fuel.
- hermitcrab 3y agoHow many orders of magnitude has the price of aluminimum come down? 3? 4? It says that a Rand study says they might be able to bring down the cost to "$6.4x10^10 per gram" with a dedicated factory. That is still so many orders of magnitude from anything financially feasible.
- master_crab 3y agoI don’t disagree. But the point I’m making is that antimatter is essentially an energy store. If you can’t find enough antimatter, you have to make it. And assuming the laws of energy conservation holds up, you need to find a better way to generate the electricity that is being used for antimatter production.
- woopsn 3y agoThere are no streaks of gamma radiation (or any sort) going across the Milky Way connecting the stars. The second issue is less obvious - the Milky Way is some 13 billion years old, has hundreds of millions of stars, but is only 100,000 light years across. Fact - the technological limitations of "today" (this century, this mya), are with empirical certainty not relevant. Interstellar voyage is not amenable to the time preferences and capabilities of the great ape. The only stuff that could transport life across the galaxy does so slowly and without propulsion.
- euroderf 3y agoWell, think about it. In fusion and fission, you're only converting a tiny tiny fraction of the atoms' masses to energy. And then to make antimatter, you want to reconstitute this tiny fraction as entire particles. IANAP (I Am Not A Physicist) but it seems like the only "realistic" way to create lightspeed-propulsion quantities of antimatter might be to convert entire planetoids and planets to iron.
- jcul 3y ago> 1 banana produces a positron ~ every 75 minutes
- antiquark 3y agoPage 26 estimates the cost of antimatter production: six trillion dollars per milligram!
- GordonS 3y agoThis is absolutely fascinating, though this isn't my field. Are any of the concepts presented feasible? Is mass-production of antiprotons on Earth realistic?
- Sharlin 3y agoIn the sense that we can currently produce and store some millions of antiprotons at a time, using a proton accelerator "merely" around 200m in diameter. Not in the sense that it would be anywhere near feasible to produce and store even a microgram worth of antimatter.
- gus_massa 3y ago> store some millions of antiprotons at a time I agree, but for scale I want to add that a glass of water has like 1000000000000000000 millions of protons in it.
- pyinstallwoes 3y agoSo, what is antimatter?
- Thiez 3y agoSome particles, such as protons and electrons, have an 'anti' version. When a particle meets its anti-version they annihilate, releasing energy in accordance to their mass (with the famous E=mc^2 formula). It's still a bit of a mystery why there was more matter than antimatter when the universe began.
- pyinstallwoes 3y agoIt’s physically measured by an instrument?
- tsimionescu 3y agoYes - you can measure the mass and electrical effect of a positron just like you can measure the mass and electrical effects of an electron (a positron is perfectly equivalent to an electron in all known ways except that it has positive charge instead of negative charge, so it would be repelled away by an atomic nucleus, and it would be attracted by an electron).
- pyinstallwoes 3y agoSo there’s an anti positron that has been measured to exist? Where do “anti” things exist? It seems closer to phase cancellation than an anti-thing. Like two sine waves out of phase.
- Thiez 3y agoThe anti positron is literally the common electron. If you want to learn more about the subject I would recommend wikipedia, it has a lot of information about quantum mechanics.
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- at_a_remove 3y agoIf we had ham, we could have ham and eggs, if we had eggs. Another classic "this will be easy as long as we have unobtanium" concept. I've been baffled, though, by the insistence on this kind of antimatter production. Antimatter production is inherently expensive because we are fighting conservation of baryon number, conservation of lepton number, et al. Physics does have one theoretical method around this, which never seems to be addressed for these proposals, and that's the baffling issue of black holes having no hair. You throw whatever past the event horizon, all that is conserved is mass, angular momentum, and charge. Baryon number, lepton number, strangeness ... all lost. Re-emission as Hawking radiation, it is thought, would simply be this sort of thing, redistributed without regard to what went in, so long as mass, angular momentum, and charge are accounted for. You would conceivably get out as much antimatter as matter. Now, that's worth looking at. And not from a "we JUST need to capture an itty black hole" (the word "just" does an enormous amount of lifting here) perspective. Rather, passage through the event horizon somehow strips off (we think, some think it might be preserved in some fashion) all of the variables which account for matter versus antimatter. And yet the event horizon isn't a hunk of matter, it's a ... membrane, a boundary, generated by matter at some distance (as a function of our usual three variables). Somehow, this warpage of spacetime operates on matter, shaving it so it has no hair. That's what fascinates me, in the sense of the theoretical having some extremely juicy practical results.
- codethief 3y ago> Baryon number, lepton number, strangeness ... all lost. Even for classical black holes I don't think that's the consensus among physicists. The general assumption seems to be that quantum numbers are still conserved when you throw stuff into black holes, just like electrical charge. Now, as for Hawking radiation, it's worth pointing out that Hawking's calculation only works for large black holes (low curvature near the event horizon). Once a large BH has shrunken down to a tiny BH (-> high curvature at the event horizon), the calculation no longer works and it is unclear what will happen. Some people say the BH will evaporate completely, some say there will be a remnant – who knows. (Both solutions have their issues.) All in all, I'm skeptical of the "shaving" you describe.
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- aimonster2 3y agoAntimatter moves mass not space. Its a no-go because of all of the issues--time dilation? You need to move space, but we still haven't found a way to fully create negative energy.
- hermitcrab 3y ago>Antimatter moves mass not space. I have no idea what that means. Care to clarify?
- ncallaway 3y agoI believe they’re saying that antimatter functions, essentially, as a normal fuel (although an amazingly dense one, far surpassing the energy density of anything else we’ve ever used as a fuel). But it, ultimately, has all the drawbacks that are inherent to “normal” fuels. But there have been proposals for other ways of traveling through space, that involve manipulating space itself, so the distance between point A and point B are smaller. Think of wormholes, or similar. One such proposal is the Alcubierre drive, which warps space around it to cause the total distance traveled to get from point A to point B to be much smaller. But such exotic drives require exotic forms of matter that we have no evidence of
- hermitcrab 3y agoThat makes sense, thanks. IIRC The Alcubierre drive would require a significant fraction of the mass-energy of the entire universe to work. We need a Douglas Adams-style infinite improbability drive!
- Simon_ORourke 3y agoI thought antimatter efficiently turns mass into energy?
- aoeusnth1 3y agoIt’s a no-go because it’s not a fantasy impossible drive?
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- hermitcrab 3y agoSummary, as I understand it: -anti-matter is incredibly difficult to produce (the total produced so far in labs is about enough to boil 1 litre of water) -anti-matter is incredibly expensive to produce (currently around 1 trillion USD per milligram) -anti-matter is very difficult to store and manage -a lot of the energy will be given off as high energy gamma rays, which will be difficult to convert into thrust -the high energy gamma rays will be very destructive to the spacecraft and crew (biological or robotic) without lots of shielding -over a ton of anti-matter would be required to get a ton of payload to a nearby star at ~40% the speed of light So don't start saving up for a ticket on an anti-matter spaceship. Or maybe do start saving, so your ancestors can take advantage of compound interest to buy a ticket in a few millenia, if we ever manage to develop the technology.
- jvanderbot 3y ago1/1 Fuel/Payload to hit 40% C is why it's going to be a trope forever. In Count to a Trillion, a small group found a way to siphon antimatter off a natural source and effectively ruled the world forever due to the near limitless energy and fast interstellar travel.
- hermitcrab 3y agoI think the issue is more the cost of the anti-matter than the fuel to payload ratio. Chemical rocket people can only dream of 1:1 fuel to payload. Look how much Saturn V + fuel to took to get a tiny payload to the moon and back.
- jvanderbot 3y agoThe issue is the cost. But the trope is "Well if we could manage the cost, 1/1 will actually get us places." As opposed to more conventional solutions, which require 1e5 / 1, or more, or more magical ones, that make no sense.
- hermitcrab 3y agoOk, I misunderstood what you were saying. I think we agree. ;0)
- bananapub 3y agoobviously it's not relevant to our interests for probably hundreds of years still, but it's a very conceptually simple proposition: 1. antimatter is incredibly energy dense, so would be an excellent fuel. 2. there's essentially none of it sitting around, so we need to make it, which takes lots of energy, but that's fine - it's an energy transport system, not an energy production system. 3. just set up square kilometers of solar panels in orbit around the sun or Mercury, use them to power particle accelerators which produce antimatter. the sun emits enormous amounts of energy - we don't need some magic new energy source, just magic new ways to temporarily bundle up energy in a dense form. edit: someone did the maths[0]: > Where will we get the energy to run these magic matter factories? Some of the prototype factories will be built on Earth, but for large scale production we certainly don’t want to power these machines by burning fossil fuels on Earth. There is plenty of energy in space. At the distance of the Earth from the Sun, the Sun delivers over a kilowatt of energy for each square meter of collector, or a gigawatt (1,000,000,000 watts) per square kilometer. A collector array of one hundred kilometers on a side would provide a power input of ten terawatts (10,000,000,000,000), enough to run a number of antimatter factories at full power, producing a gram of antimatter a day. from TFA: > Preliminary mission analysis: > - 10 kg instrument payload could be sent to 250 AU in 10 years using 30 mg of anti-H > - A similar probe could be sent to Alpha Centauri in 40 years using grams of anti-H [0]: https://worldbuilding.stackexchange.com/questions/240278/how-would-we-make-antimatter-in-industrial-quantities https://worldbuilding.stackexchange.com/questions/240278/how...
- tomatotomato37 3y agoI don't get the placement of some of the technologies on the chart on page 5. How is pulsed fission being beaten out by both thermal fission and chemical rockets in terms of acceleration, considering for all intents and purposes that's propulsion by nuclear detonation? And continuous fusion is all the way on the right despite being the basis of a torchship?? It all just seems so arbitrary
- amai 3y agoUnfortunately before we will develop an antimatter drive humanity will develop an antimatter bomb, see e.g. Yoko Tsuno, The time spiral: http://shareduniversereviews.blogspot.com/2014/04/yoko-tsuno-la-spirale-du-temps-time.html http://shareduniversereviews.blogspot.com/2014/04/yoko-tsuno...
- hermitcrab 3y agoIt says: "Chemical combustion: ~ a few MJ/kg • Solid Propellants: ~ 5 MJ/kg • Liquid Propellants: ~ 1 MJ/kg" Which doesn't look right. My son (a rocketry enthusiast) tells me: "Liquid engines have energy density between 12 and 20MJ/kg. Apparently they just left off the 0 and likely meant to put 10MJ/kg"
- hermitcrab 3y agoI got a reply back from the author of the slides: "Your son is correct, that is a typo - it should be 10's of MJ/kg for liquid rocket propellants - thanks for the catch! Thanks too for the heads up re the discussion on antimatter, it is a fascinating topic and great to see there is interest in the community!"
- segfaultbuserr 3y agoAs the original submitter of this URL, I'm impressed.
- Ziggy_Zaggy 3y agoWow, just wow. Great work being done at NASA. Please don't retire for another 10 years (or more).