Alpha-electric and Nuclear-electric Rockets

| In an earlier report, I pointed out that a bilayer lm, one of whose sides was made of-emitting radioactive atoms, would act as a \rocket." A 3-stage alpha rocket could reach, e.g., speeds of 0:0025c in a few hundred years. (1) I now describe a simple variant I call the \alpha-electric rocket." It uses alpha rays to charge a capacitor which powers an ion gun. If it works, it should be able to reach 5 higher speeds than comparable alpha rockets. We describe 1-stage designs reaching (0:007-0:012)c in 300 years or (0:005-0:009)c in 6 years. But it may not work, due to charge leakage problems. That question should be highly amenable to experiment. (2) The \nuclear-electric rocket" consists of a nuclear chain reactor generating electricity to power an ion gun. With optimistic assumptions, it could achieve speeds of 0:0006c in 100 years { but probably various engineering constraints will reduce that speed estimate by a factor of 4. Thus, the nuclear-electric rocket indeed isn't competitive in speed, at least if required to reach that speed in 100 years. But speeds of 0:005c could be reached by nuclear-electric rockets running at extremely low power levels for 10000's of years. Nuclear-electric rockets would enjoy great exibility advantages (i.e. the ability to turn them on and oo at will; possible \refueling" with more expellable mass) versus rockets, but would suuer from much greater complexity and unreliability. Along the way, we will derive some new kinds of \rocket equations" and invent some new kinds of ion sources and energy conversion devices.