08-29-2017, 10:11 PM | #11 | |
Join Date: Feb 2007
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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The result would be a rocket that produced very little radiation but could in theory give bountiful thrust. In practice, we're a long way from being able to build such a thing, we don't know how to store tiny amounts of seetee in reasonably-massed/volume storage systems, and we'd have to make the antimatter at high expense. But it's possible in principle, and if we could built it it wouldn't be devastating to its launch area. You'd probably want to launch it in open areas, like a patch of desert, but it wouldn't be a WMD for the launch site.
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08-29-2017, 11:37 PM | #12 |
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
Sure, but such systems would actually be poor rockets compared to straight antimatter rockets with gamma exhaust. Which means that you aren't going to use the same engine for lift that you use for deep space burns, or at least your engine has two modes, one with significantly poorer ISP.
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08-30-2017, 12:01 AM | #13 |
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
It's always thrust vs. reaction mass economy.
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08-30-2017, 12:50 AM | #14 |
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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08-30-2017, 06:32 AM | #15 | |
Join Date: Jun 2006
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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Since the reaction mass, and hence its energy content, must be contained in at least some directions to get any thrust out of it, and the energy content of a system is limited by the strength of the materials resisting that energy blowing it apart (the Virial theorem), the maximum thrust to weight ratio you can physically achieve goes down as the energy content per unit thrust goes up.
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08-30-2017, 07:04 AM | #16 |
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
Assuming that one method isn't significantly more efficient at converting fuel mass into energy, which I don't think is the case here, when one is annihilation reactions and the other is boiling water.
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08-30-2017, 12:11 PM | #17 | |
Join Date: Jul 2008
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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One expells the annihilation products directly, the other uses them to heat (water) reaction mass, yes. The water reaction mass will almost certainly be much lower ISP than the annihilation product reaction mass...but it's also a lot easier to confine, so it's very likely you can get much higher thrust out of it. I mean, really, what you're talking about is right on SS23: Antimatter Thermal Rocket vs. Antimatter Pion.
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08-30-2017, 12:36 PM | #18 | |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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However, there's another factor that causes higher ISp to have lower thrust: thermal limits. If you've got a physical nozzle, the reaction mass can't be so hot that it melts or corrodes the nozzle (this generally caps ISp at 1-2k for hydrogen reaction mass, much worse for anything else). Whether or not you've got a physical nozzle, you are limited by your ability to get rid of waste heat (this generally limits high ISp designs to fairly low power density; low ISp designs use reaction mass as coolant, but for high ISp the heat capacity of the reaction mass is inadequate). |
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08-30-2017, 02:02 PM | #19 | |
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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(I have a strong tendency to hyperbole, but usually try to restrain myself in text.) But even with a total mass annihilation drive like antimatter, I think large amounts get lost by way of ejecta that can't be used for propulsion. But as has been said, nearly any effective rocket is an even more effective weapon. No plausible drive to gently lift and push a ship into space exists that I know of.
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08-30-2017, 03:27 PM | #20 | |
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Re: [Spaceships] Anti-Lithium for Drives – Does this work?
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