On Sat, Feb 21, 2009 at 1:35 PM, Onno Meyer <[email protected]> wrote: >> Vehicles is missing a trick here, it appears. It's quite possible to >> use air-breathing fusion rockets, which then use something else >> (water, hyrdrogen are the usual choices, but you can use other things) >> as reaction mass when you get out of the atmosphere. > > Those are called fusion ram-rockets. Since they function as > fusion rockets in space, I didn't list them separately. >
Ah. That's the way to go, I'd think. >> The exhaust from >> fusion rockets needn't be terribly radioactive. A D-3HE fusion >> reactor is fairly low radiation output. >> David Scheidt >> [email protected] > > Talking about radiation, "fairly low" doesn't sound all that > reassuring, expecially if space traffic starts to rival air > traffic today. Consider what happened to nuclear freighters. It really matters what kind of radiation you're talking about. A D-3He fusion reactor uses two inert (well, one of them is inflammable) gases as fuel. The primary products are heat, a proton, an alpha particle, and some X rays. Most of the Xrays will be absorbed by the shell of the reactor, as they're radiated pretty equally in all directions. One end of a fusion rocket is open, so there will escaping Xrays in that direction. They'll get absorbed (as heat) by the atmosphere in less distance than the exhaust will kill anything the plain old-fashioned way: by setting it on fire. The proton and alpha particle will be indistinguishable from the very high temperature air or other reaction mass that's being shot out the back. There are essentially no long-lasting sources of radiation there. Setting things on fire is much more of a problem. The exhaust temperature is very high. For things that act something like airplanes (with wings or lifting bodies) they can use the air-ram as a sort of ducted fan until they're well air borne, and then turn on the full power. Fission reactors, on the other hand, produce lots of particles that hang around and emit radiation for (days/months/years/centuries), depending on the particular reactions involved. (They could be used in a fully-closed thermal only mode, but I don't think they'd produce enough thrust that way.) -- David Scheidt [email protected] _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
