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The natural fit here is a naval nuclear reactor. For example, the A4W reactor on a Nimitz-class aircraft carrier puts out 550MW(th), and of course it has a cont

The natural fit here is a naval nuclear reactor. For example, the A4W reactor on a Nimitz-class aircraft carrier puts out 550MW(th), and of course it has a continuous 100% duty cycle, and 20 years of operating time before requiring refueling. For slightly less overkill, an S6G reactor from a Los Angeles-class nuclear sub puts out 165MW(th), and is substantially smaller and lighter. Of course, this raises some thorny issues around potential launch failures spreading radioactive material over a large area. This is already a consideration even with the little RTGs that NASA launches for rovers.

jaggederest 8y ago
I'd expect that's about the size of the problem. Putting an aircraft carrier on mars, but with the carrier deck used to grow food, and the "propulsion" energy going to electrolyse and feed forward into the sabatier process. Give it 3-5 of the A4W reactors for "a year between transit windows" redundancy, and you're starting to get into the ballpark. Putting a pair of $13 billion dollar, 110,000 ton nuclear vessel on mars would "only" cost $110bln. A steal, really, when you think about it.
- gotocake 8y ago
  It would cost a lot more, that’s just the cost of lift raw tonnage of the carriers themselves. You also have to lift the machinery to assemble and maintain them, spares of pretty much everything, and the cost of developing and lifting all of that. I think we’d all be looking at the “modest” billions inflate into enormous trillions before we knew it. Of course if it actually worked it would potentially be worth it.
philipkglass 8y ago
The natural fit here is a naval nuclear reactor. ... Of course, this raises some thorny issues around potential launch failures spreading radioactive material over a large area. This is already a consideration even with the little RTGs that NASA launches for rovers. Counter-intuitively, a nuclear reactor has lower radiotoxicity risks in case of an explosion during launch. Before a reactor reaches criticality for the first time, it doesn't contain any highly radioactive materials. It's only as radioactive as its uranium fuel. Uranium has a long half-life and corresponding low radioactivity. Plutonium 238, used in RTGs like that in the Mars Science Laboratory, has a half life of 87.7 years. Uranium 235 has a half life of 704 million years. Neglecting differing relative biological effectiveness of radiation for the moment, that means that the plutonium 238 in RTGs is about 8 million times more radioactive, kilogram-for-kilogram, than the uranium 235 in a reactor's fuel. The Mars Science Laboratory carried 4.2 kilograms of plutonium 238 (4.8 kg of PuO2): https://www.nasa.gov/pdf/532433main_FIN%20MSL%20Launch%20Nuclear%20Safety%20FS%202-9-11.pdf https://www.nasa.gov/pdf/532433main_FIN%20MSL%20Launch%20Nuc... It could have carried 33.7 million kilograms of U-235 for roughly the same radiological risk. Or, realistically, missions could launch with reactors designed for a few tens of kilowatts to megawatts and the maximum radiological risk would be much smaller than with RTGs. At least so long as the reactor attains first criticality after the risky launch phase.
- mLuby 8y ago
  Really interesting point! Since nuclear reactor is unfortunately a tainted term, maybe we just need to rename it to something more technical, like RTG. Space-worthy Inert Radioisotope Power Plant?
walrus01 8y ago
> The natural fit here is a naval nuclear reactor. As addressed in some popular science fiction, Robinson's "Red Mars" has the first mars colony outfitted with what is described as basically a nuclear submarine reactor. To the extent that they describe it as a "Rickover" class reactor.

jaggederest 8y ago

I'd expect that's about the size of the problem. Putting an aircraft carrier on mars, but with the carrier deck used to grow food, and the "propulsion" energy going to electrolyse and feed forward into the sabatier process. Give it 3-5 of the A4W reactors for "a year between transit windows" redundancy, and you're starting to get into the ballpark. Putting a pair of $13 billion dollar, 110,000 ton nuclear vessel on mars would "only" cost $110bln. A steal, really, when you think about it.

gotocake 8y ago
It would cost a lot more, that’s just the cost of lift raw tonnage of the carriers themselves. You also have to lift the machinery to assemble and maintain them, spares of pretty much everything, and the cost of developing and lifting all of that. I think we’d all be looking at the “modest” billions inflate into enormous trillions before we knew it. Of course if it actually worked it would potentially be worth it.

philipkglass 8y ago

The natural fit here is a naval nuclear reactor. ... Of course, this raises some thorny issues around potential launch failures spreading radioactive material over a large area. This is already a consideration even with the little RTGs that NASA launches for rovers. Counter-intuitively, a nuclear reactor has lower radiotoxicity risks in case of an explosion during launch. Before a reactor reaches criticality for the first time, it doesn't contain any highly radioactive materials. It's only as radioactive as its uranium fuel. Uranium has a long half-life and corresponding low radioactivity. Plutonium 238, used in RTGs like that in the Mars Science Laboratory, has a half life of 87.7 years. Uranium 235 has a half life of 704 million years. Neglecting differing relative biological effectiveness of radiation for the moment, that means that the plutonium 238 in RTGs is about 8 million times more radioactive, kilogram-for-kilogram, than the uranium 235 in a reactor's fuel. The Mars Science Laboratory carried 4.2 kilograms of plutonium 238 (4.8 kg of PuO2): https://www.nasa.gov/pdf/532433main_FIN%20MSL%20Launch%20Nuclear%20Safety%20FS%202-9-11.pdf https://www.nasa.gov/pdf/532433main_FIN%20MSL%20Launch%20Nuc... It could have carried 33.7 million kilograms of U-235 for roughly the same radiological risk. Or, realistically, missions could launch with reactors designed for a few tens of kilowatts to megawatts and the maximum radiological risk would be much smaller than with RTGs. At least so long as the reactor attains first criticality after the risky launch phase.

mLuby 8y ago
Really interesting point! Since nuclear reactor is unfortunately a tainted term, maybe we just need to rename it to something more technical, like RTG. Space-worthy Inert Radioisotope Power Plant?

walrus01 8y ago

> The natural fit here is a naval nuclear reactor. As addressed in some popular science fiction, Robinson's "Red Mars" has the first mars colony outfitted with what is described as basically a nuclear submarine reactor. To the extent that they describe it as a "Rickover" class reactor.