12-07-2017, 05:08 PM | #21 | |
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Join Date: Oct 2004
Location: Forest Grove, Beaverton, Oregon
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Re: [Spaceships] Mass-driver realism
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Panic and politics would be the true dangers, and very real too.
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12-07-2017, 06:18 PM | #22 |
Wielder of Smart Pants
Join Date: Aug 2004
Location: Ventura CA
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Re: [Spaceships] Mass-driver realism
You can't detonate a thermonuclear device without a primary fission device.
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12-07-2017, 08:36 PM | #23 | |
Join Date: Aug 2007
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Re: [Spaceships] Mass-driver realism
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Fission on the other hand puts out 94% of its' energy in the form of charged particles. I'm sure that pure fusion is possible in theory but I'm not at all sure that it makes for practical explosions large enough for Orion. The National Ignition Facility https://lasers.llnl.gov/about/what-is-nif doesn't make for very large explosions at all and it's bit heavy even for optimistic Orions.
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Fred Brackin |
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12-07-2017, 08:43 PM | #24 |
Join Date: Feb 2016
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Re: [Spaceships] Mass-driver realism
But you can detonate a pure fusion device without a fissionable element because it is not thermonuclear. As I said, you want to use something else that tritium (50% of the D-D reactions create tritium, which is consumed by secondary fusion reactions and produces the problematic neutrons). You would want either He-3 + He-3 or p + Be-11 (there are proponents of p + Li-7, but around 10% of the reactions instead produce n + Be-7 instead of 4 He, which means that the n produced by the reaction ends up having an energy equivalent to the n from a D + T reaction). Presumably, the device would depend on compression caused by metallic hydrogen detonated by a conventional explosive (Orion is an external explosion, so you cannot use lasers or ion beams with any reasonable chance of success for detonation).
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12-07-2017, 09:28 PM | #25 | |
Join Date: Aug 2007
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Re: [Spaceships] Mass-driver realism
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Fusion without heat would require something like meson catalysis and we don't have a miraculous source of mesons right now. I'm generally familiar with aneutronic fusion reactions being a veteran of Transhuman Space but the even in that setting's 2100 AD the fusion pulse drives they use are still quite optimistic and still not useful for launching from Earth's surface. They definitely not something we could have today if we'd spent just a little bit more money.
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Fred Brackin |
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12-07-2017, 10:41 PM | #26 |
Join Date: Feb 2016
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Re: [Spaceships] Mass-driver realism
Fusion caused by metallic hydrogen compression, inertial compression, magnetic compression, etc is not generally considered thermonuclear because it does not involve a fission explosion.
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12-08-2017, 01:38 AM | #27 | |
Join Date: Sep 2008
Location: near London, UK
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Re: [Spaceships] Mass-driver realism
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If you are interested in Orion, the absolutely necessary book is George Dyson's Project Orion: The True Story of the Atomic Spaceship. Highly recommended.
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12-08-2017, 09:33 AM | #28 | |
Join Date: Aug 2007
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Re: [Spaceships] Mass-driver realism
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To my understanding "thermonuclear" exists to distinguish reactions caused by heat from those initiated by neutrons.
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Fred Brackin |
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12-08-2017, 10:11 AM | #29 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Spaceships] Mass-driver realism
Even assuming that definition was true, it's somewhat irrelevant. What we care about is the quantity of radioactive material generated, which is a combination of fragments of the bomb itself that are radioactive (this is mostly from the fission component, though you presumably get some tritium release) and neutron activation of materials exposed to the bomb (fusion generally produces more of these than fission, though it depends significantly on fuel mix and completeness of burn -- the cycle n+Li6 -> 4He+T, T+D -> 4He+n doesn't actually produce any net neutrons, but some neutrons always escape).
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12-08-2017, 06:12 PM | #30 |
Join Date: Dec 2017
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Re: [Spaceships] Mass-driver realism
Theoretically, you can build a clean fusion bomb - you use a "burn" of pure He-3, (current thermonuclear bombs use a Tritium( H-3) Deuterium (H-2) mix), and you use non-fission methods of achieving the compression/heating (the difference between them is theoretical at the energies needed) for fusion to initiate. The He-3 He-3 reaction is He-3 + He-3 → He-4+ 2 protons. This means no radiation, just heat. As such, the device would be completely clean in it's primary reaction, making an Orion launch fine and dandy.
However, the difficulty is getting a He-3 He-3 reaction, which requires much higher effective temperatures than H-2 +H-3. Certainly not achievable at current TL-8... |
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