[Spaceships] Fusion Rockets

Neural Kernel · 10-31-2010, 09:13 PM

tshiggins laid it out better than I could in terms of the socio-economic impact of a more efficient drive, not only am I currently missing my book (I'll get it back soon, I hope...) but the large scale social interactions of THS never really were my main focus.
From what I remember of "Spaceships" the fuel AND reaction mass of a fusion rocket is assumed to just be hydrogen, no distinction is made between fuel or reaction mass. Hydrogen is likely the reaction mass of choice in THS fusion rockets but the fuel is a separate matter, it is either two different isotopes of hydrogen (deuterium and tritium) or else deuterium and helium3. D-T fusion produces roughly the same energy (I think...) as he3-D reactions but also produces neutron radiation which requires heavy shielding. Since he3-D fusion is largely free of the neutron "problem" it can dispense with the shielding, making a much lighter reactor/engine, meaning higher performance. The drawback is, of course, that he3 is extremely expensive. D-T is almost free by comparison, deuterium is plentiful wherever there is hydrogen (icy asteroids, gas giants, seawater...) and tritium can be bred by neutron bombardment of lithium (a D-T reactor can use it's own neutron production to create more fuel). With a fusion rocket taken literally as written... just load it with hydrogen and go... the entire economic system of the Solar system falls apart. If we assume that the actual fuel used is still he3-D or D-T and it's only hydrogen as reaction mass then you need two varieties of fusion rocket to accurately model THS drives, a high performance rocket with high fuel costs along with a lower performance rocket with MUCH lower fuel costs. Really the only reason to use he3 is if you're in a hurry or need to worry about environmental effects, basically Earth's power systems and military/passenger ships. Of course the best fuel (distinct from reaction mass) is still antimatter, I doubt there are many pion rockets flying but even a few grams of antihydrogen would dramatically improve the performance of a fusion rocket, although you would need shielding and quite a bit of radiator capacity to take advantage of it.
The primordial black hole(s?) found in the Kuiper belt are the most interesting development I remember from THS... not quite total conversion but potentially super fusion... at least for reactors if not rockets (cheap antimatter!!)
http://www.orionsarm.com/eg-article/49a58545cf19f

10-31-2010, 09:13 PM	#4
Neural Kernel Join Date: Jul 2010	Re: [Spaceships] Fusion Rockets tshiggins laid it out better than I could in terms of the socio-economic impact of a more efficient drive, not only am I currently missing my book (I'll get it back soon, I hope...) but the large scale social interactions of THS never really were my main focus. From what I remember of "Spaceships" the fuel AND reaction mass of a fusion rocket is assumed to just be hydrogen, no distinction is made between fuel or reaction mass. Hydrogen is likely the reaction mass of choice in THS fusion rockets but the fuel is a separate matter, it is either two different isotopes of hydrogen (deuterium and tritium) or else deuterium and helium3. D-T fusion produces roughly the same energy (I think...) as he3-D reactions but also produces neutron radiation which requires heavy shielding. Since he3-D fusion is largely free of the neutron "problem" it can dispense with the shielding, making a much lighter reactor/engine, meaning higher performance. The drawback is, of course, that he3 is extremely expensive. D-T is almost free by comparison, deuterium is plentiful wherever there is hydrogen (icy asteroids, gas giants, seawater...) and tritium can be bred by neutron bombardment of lithium (a D-T reactor can use it's own neutron production to create more fuel). With a fusion rocket taken literally as written... just load it with hydrogen and go... the entire economic system of the Solar system falls apart. If we assume that the actual fuel used is still he3-D or D-T and it's only hydrogen as reaction mass then you need two varieties of fusion rocket to accurately model THS drives, a high performance rocket with high fuel costs along with a lower performance rocket with MUCH lower fuel costs. Really the only reason to use he3 is if you're in a hurry or need to worry about environmental effects, basically Earth's power systems and military/passenger ships. Of course the best fuel (distinct from reaction mass) is still antimatter, I doubt there are many pion rockets flying but even a few grams of antihydrogen would dramatically improve the performance of a fusion rocket, although you would need shielding and quite a bit of radiator capacity to take advantage of it. The primordial black hole(s?) found in the Kuiper belt are the most interesting development I remember from THS... not quite total conversion but potentially super fusion... at least for reactors if not rockets (cheap antimatter!!) http://www.orionsarm.com/eg-article/49a58545cf19f