dietz%USC-CSE@USC-ECL.ARPA (04/04/84)
Thanks to ota for sending me a copy of Roderick (NOT Robert) Hyde's paper. The paper makes these points: The Daedalus study claimed that D+He-3 is superior to DD or DT fuel because the reaction products are chared particles. Hyde argues that this isn't so, because (a) the reactions D+D -> He-3+n and D+D -> T+p (followed by D+T->n+He-4) will still occur, (b) in the highly compressed pellets used in inertial confinement fusion most of the high energy neutrons from D+T reactions will deposit their energy in the pellet before escaping, but (c) enough netrons escape in any case to require neutron shielding, even with D+He-3. Also, (d) at the higher temperatures needed for D+He-3 fusion, a significant amount of X-radiation from bremmstrahlung is generated. As a result, the Daedalus thrust chamber design won't work, because it intercepts many of the neutrons, gamma rays and X-rays, leading to unacceptable heat dissipation requirements. Also, the Daedalus thrust chamber won't direct the plasma nearly as well as advertized, leading to lower thrust. Hyde uses a single, well-shielded superconducting coil to form the magnetic nozzle. A lithium shield is used to generate tritium in flight to catalyze deuterium pellets. Some 4 GW of power is dissipated in the coil shield, which is carried away to the radiators by liquid lithium. Hyde proposes krypton fluoride lasers as drivers due to their high operated temperature (1000 degrees K) which reduces radiator mass. Total vehicle mass is 486 tons. Theoretical maximum exhaust velocity is about 8.7% c, but in practice lower because of energy lost in neutral particles, nozzle inefficiencies and because not all the pellet is fusion fuel. The exhaust velocity of the rocket can be adjusted by wrapping the pellets in extra nonfusionable mass. The rocket can take 1500 tons of payload to Mars in 22.2 days, to Jupiter in 93.6 days and to Pluto in just under a year. Maximum thrust is 3 million newtons. Hyde's rocket would make a fine asteroid tug, although it isn't optimized for this function. It could accelerate a 100,000 ton asteroid to 4 km/sec in 37 hours. By using asteroid mass for shielding, structural material and reaction mass, higher thrust should be possible.