Background: The Orion spacedrive was a theoretical concept.  It
would be a drive using thermonuclear explosions to drive a spacecraft.
The idea was that you'd detonate devices with somewhere from one to
ten megatons yield behind a "pusher plate" attached to the main
spacecraft.  The shock wave from the explosions would transfer
momentum to the ship.

  Now, in an atmosphere I can see this.  The energy of the explosion
heats the atmosphere, which expands explosively and slams a shock wave
into the pusher plate.  But in a vacuum, only two things I can see are
going to hit the plate: fission/fusion products (barium, krypton,
helium, neutrons, evaporated bomb casing) and electromagnetic
radiation (gammas mostly, some light/heat from irradiated fission
products).

  Would this work?  I can't see the EM radiation impelling very much
momentum (especially given the mass of the pusher plate), and it seems
to me you're going to get more momentum transfer throwing the bombs
out the back of the ship than you get from detonating them once
they're there.

  I must be missing something.  Would someone enlighten me via email?

  Thanks.

-- 
	--Jim
