>As for space usage, launch weight restrictions make LWR style reactors impractical. OK, so this is a reply to both you and @nickelpro (your comment is newer b

>As for space usage, launch weight restrictions make LWR style reactors impractical. OK, so this is a reply to both you and @nickelpro (your comment is newer but also higher), who wrote: >Space-based nuclear energy is all based around RTGs, reactors have no place in space You both seem to have an image in your heads regarding future long duration deep space vehicles (I explicitly mentioned "outer solar system") here that is a mixture of old space assembly and soft science-fiction, wherein industrial capacity is all terrestrial and any ship is built entirely on Earth, launched and off it goes. All-in-one. Even SpaceX with its use of pure chemical rockets to Mars and terrestrial construction plans to break with that: in-orbit refueling is an absolutely key part. And for going farther then that (and as Starship and successors/competitors kick starts a new era of space economics and industry) the clear and necessary next step will be in-space assembly (be it in LEO or a Lagrange point dock or whatever ends up being most practical at a given time). In the same way we don't expect our ships to somehow be built hundreds of miles inland and then make their way to the ocean or fit entirely on a single semitruck, stay indefinitely on what can be launched out of Earth's atmosphere makes no sense either. The important aspects are all at cross purposes. Aerodynamic considerations are a waste in vacuum and constrict design in very important ways. Engines to get out of a strong gravity well need high thrust, whereas for long distances in space one really wants very high ISP. A torch drive that can do both necessarily bears a striking resemblance to a high energy weapon system to whatever happens to be facing the business end of it, and all known practical models (nuclear salt water, thermonuclear pulse) are ludicrously polluting. And outer solar system ships will need strong variable electric sources with high power/mass too despite solar being entirely impractical. RTGs won't cut it. So sure I don't think we'll ever see one launch off Earth's surface (I hope not anyway, if humanity is willing to light one of those off here it means we're facing a threat big enough that trashing our home is considered worth it). But that's a-ok, because what we'll do is built empty reactors, or reactor components, and launch those separately from fuel, and put it all together in space. Or for that matter far enough down the road maybe we build that stuff on the moon or in the asteroids or who knows. It obviously wouldn't be a copy/paste, but to the extent that USN reactor designs will get used outside of the military that's where I see it making sense.