Posts by John DuBois

Russia planning nuclear-powered manned spaceship

A good move

If they really want to "maintain a competitive edge in the space race", this is a good direction to take, since they have little to worry about in the way of competition from the west - public opinion in the US and Europe has and will continue to prevent any serious moves in this direction. So we'll continue to poke along with our chemical or solar or itty-bitty-RTG powered spacecraft, while Russia has the opportunity to take the large-scale/high-performance arena for itself (unless the Chinese decide to get involved). That it would decide to spend the rubles to exploit that opportunity is probably too much to hope for.

Space nuke boffin: NASA Moonbase needs nuclear rockets

radioactivity, hydrogen...

Not sure about Nerva, but in the case of the Dumbo design, the radioactive material that could end up in the exhaust was not the reaction mass itself but rather the daughter products of the fission reactions - the requirement for a very low barrier to heat exchange meant that some of them could reach the reaction mass. Nerva may have had the same issue.

Hydrogen is used as reaction mass because, for a given exhaust temperature (as set by the engine design, and the requirement that it remain solid!), hydrogen gives the highest specific impulse. "Easier to store" materials may actually give a lower specific impulse than chemical engines.