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NASA Looking At Nuclear Thermal Rockets To Explore the Solar System
MarkWhittington writes: Officially, NASA has been charged with sending astronauts to Mars sometime in the 2030s. Toward that end, according to a story in Universe Today, space agency engineers at the Marshall Space Flight Center are looking at an old concept for interplanetary travel, nuclear thermal engines. "...according to the report (cached), an NTP rocket could generate 200 kWt of power using a single kilogram of uranium for a period of 13 years – which works out of to a fuel efficiency rating of about 45 grams per 1000 MW-hr. In addition, a nuclear-powered engine could also provide superior thrust relative to the amount of propellant used." However, some doubts have been expressed whether NASA will be granted the budget to develop such engines.
An Ion thruster (of any variety) is not *remotely* a replacement for a nuclear thermal engine. The ISP is great but the thrust levels are (and always will be, at rational sizes) feeble. And it's very likely that massively clustering them to get the thrust up will required a nuclear reactor to power them. 6/10ths of an *ounce* of thrust for 4 kW power input.
Ion thrusters have their uses, like in gently nudging things over long periods. They are not going to replace chemical rocket or NTP engines for any sort of high-thrust application.
If only someone had been launching small quantities of radioisotopes into space for many decades and perfected the containment vessels... Oh wait, they have. They're called RTGs and they're absolutely designed to survive the rocket exploding on launch pad or free-fall from space after a failed launch. There has never been an incident where an RTG has leaked radioactive material into the environment. Not that it would matter - the amount we're talking about here is equal to the amount of uranium released into the environment by a coal-fired power plant every two hours in normal operation.
If the rocket it's on explodes for some reason you've got a bit of a mess here on Earth. I think it's a valid concern.
No it isn't. A common mistake, but uranium is barely radioactive at all. Perhaps you are thinking of the plutonium RTGs in deep space probes or Mars rovers?
Or reactor waste products? But no, the clean uranium fuel loaded into the reactor is quite harmless.
If the reactor is run for a few years, then crashes into earth, you get a big mess.
Open cycle nuclear engines are a bad idea anywhere close to earth orbit. They are essentially an open system that expells nuclear fission byproducts as well as propellant. They are not permitted to operate in earth orbit for a good reason. They would leave significant trails of radioactive material in orbit. This has implications for the sensors on satellites and is still going to fall to earth eventually. So these open cycle reactors may be useful for longer missions but would still need to get a heavy reactor into orbit. They also run essentially unshielded so on a manned mission you'd need lead or water shielding. Nuclear power sources using decay heat are probably better suited due to low levels of gamma an neutron radiation. The idea of collecting propellant along the way is quite attractive too but beyond our current engineering. http://en.m.wikipedia.org/wiki...
Ready for flight tests? Hrm. They could never get the core to stop cracking and expelling bits of enriched uranium out the back. That's not a small problem.