08-30-2017, 04:56 PM | #21 |
Join Date: Jun 2006
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
I'd have to think about that more. At best I think it just changes the slope of the curve - the energy content increases a lot faster (with the square of the exhaust velocity) than the residence time falls (as 1/v), but I have a sneaking suspicion there's time limit in there that's a function of the speed of sound in something between the front wall of the combustion chamber and the end of the nozzle.
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08-30-2017, 05:27 PM | #22 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
At constant thrust the mass flow rate is inversely proportional to velocity, and the residence time is also inversely proportional to velocity, so the mass in the chamber is inversely proportional to the square of velocity. The energy per unit mass is proportional to the square of velocity, and thus the energy in the chamber is constant (it's just pressure * volume * a constant that depends on how closely the propellant resembles an ideal gas).
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08-30-2017, 05:52 PM | #23 | |
Join Date: Jul 2008
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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An antimatter thermal rocket isn't necessarily the best liftoff engine by the book since it's got only 0.4 G thrust per system, but you can use it and it's not particularly egregious - its backblast is just rather hot hydrogen, not anything particularly nasty.
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08-30-2017, 07:22 PM | #24 |
Join Date: Feb 2016
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
Antilithium should not really have any benefits (antimatter-matter reactions become problematic because of kaon, muon, and pion radiation after they get beyond position-electron reactions [which are the only antimatter reactions that just produce gamma rays]), and it should be even more expensive than antihydrogen by orders of magnitude. Unless you are able to harvest it from a natural source (which would require very high levels of superscience to avoid becoming annihilated the moment you started mining), you would have to create antihydrogen and then fuse antihydrogen to antilithium. You would have to have a fusion reactor that could not only do proton-proton reactions but could do so using antiprotons. Is it possible? Yes, but it is not plausible by any conceivable level of technology.
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08-30-2017, 08:16 PM | #25 |
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Join Date: Oct 2004
Location: Forest Grove, Beaverton, Oregon
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
It's hard to to say what will absolutely never be done by any human culture or descendant thereof in the infinite future, let alone what no alien species will do in the entire universe ever.
If it's even remotely barely technically possible, I bet someone/something somewhere has or will eventually do it, no matter how bizarre, inefficient, or plain suicidally dumb it seems. But it does seem hard to imagine under what circumstances such a fuel would ever be economical.
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08-30-2017, 08:25 PM | #26 | |
Join Date: Jul 2008
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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I don't think making antilithium is inconcievable for TL 11. We're talking a tech level that can build a weapons-grade x-ray laser that weighs a third of a pound, here.
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08-30-2017, 09:17 PM | #27 | |
Wielder of Smart Pants
Join Date: Aug 2004
Location: Ventura CA
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
Quote:
Last edited by sir_pudding; 08-31-2017 at 02:57 PM. |
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08-30-2017, 10:30 PM | #28 | |
Join Date: Feb 2007
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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Nor do you have to use water, you could use any fluid or gas your drive could handle. Water would just be convenient. (Modulo our current inability to build such a thing, of course. But we can't build a useful gamma-photon drive, either.) If you pump out enough thrust with a gamma-photon drive to get from Earth's surface to LEO or escape, then with even a tiny spacecraft you need substantial amounts of antimatter to do it, and yes, your drive is also a WMD on a big scale. The energy-to-thrust ratio for photon drives is rotten. A photon-drive surface-to-orbit/escape vessel is theoretically possible, in the physics sense, but it uses a genuine death ray as a means of propulsion. I foresee legal and diplomatic issues. A photon drive is preferable if you're hoping to use antimatter to achieve relativistic velocities, yes. But at intra-solar and planetary velocities the tradeoff is different.
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08-31-2017, 09:21 AM | #29 | |
Join Date: Aug 2007
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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The gamma rays resulting from some of the first-stage annihilations and then the meson breakdown are not used for thrust at all. This is what makes the ^Total Conversion Drive even more fuel efficient. I'm afraid that Sir Pudding has jumped in his head to a TC drive that inconveniently emits all the converted energy as gamma rays while retaining a chemical rocket-like thrust-to-weight ratio. Not a hard science thing at all.
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08-31-2017, 09:31 AM | #30 |
Join Date: Nov 2004
Location: The plutonium rich regions of Washington State
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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