Of course, other technologies, Ion and plasma are much higher (a quick google gives an ISP of 3300 for early ion drives).
Of course, Ion and plasma are low thrust, and cannot be used for ascent or descent, but neither can NERVA class motors, as their exhaust is radioactive.
Space nuke boffin: NASA Moonbase needs nuclear rockets
By Lewis Page
Published Saturday 30th June 2007 07:02 GMT
One of America'a top nukes-in-space boffins says it's time to consider nuclear-powered rockets again. He reckons atomic boosters could cut the cost of NASA's upcoming Moonbase plan.
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This guy runs the premier RTG battery (nuclear batteries) manufacturer in the US, The Center for Space Nuclear Research, and he is someone who has a hammer, and sees everything as a nail.
But Howe reckons that there's more to nukes in space than just providing electricity. He says that nuclear power should be used for propulsion, too. According to an article in New Scientist, his plan is to update a 1960s design called Nuclear Engine for Rocket Vehicle Application (NERVA) to carry payloads from Earth orbit to the Moon.
NERVA-type rockets use a fission reactor to heat up hydrogen and blast it out of the thrust nozzle at extremely high speed, faster than can be achieved by normal chemical-powered boosters. This allows a nuclear-driven spacecraft to achieve more with a given amount of liquid fuel, or "reaction mass." The NERVA test programme had its problems - not least the fact that the reactor tended to come apart and fire itself out of the exhaust - and was terminated in 1972 during NASA budget cuts.
Howe and his team reckon that the greater efficiency of nuclear drive would allow each Moon shot to carry an additional eight tons of payload, which would mean fewer launches being needed. He thinks the savings from a lower number of launches would more than offset the cost of updating the original NERVA design, perhaps yielding overall savings of as much as $2bn.
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