A lot of your math is way off, brother. Sure, NERVA was close to 1.0 thrust to weight ratio, but that says a lot more about the state of technology at the time

A lot of your math is way off, brother. Sure, NERVA was close to 1.0 thrust to weight ratio, but that says a lot more about the state of technology at the time than about the capabilities of nuclear thermal rockets. The Dumbo / STNP engines were order of magnitude better than NERVA - way more than "half the mass" and I'm pretty sure we can do better than that these days. The quote is "Better than a conventional engine for any given amount of fuel", implying that even with balance-of-system mass issues they're still ahead of chemical rockets using virtually any fuel. Also, I don't know whether anybody is suggesting crewed missions, or at least I'm not. But "Why bother", well, cost and efficiency and size, frankly. Starship is a bold move, but to me, it looks pretty small. I'd like them to add a zero onto the end of the mass budget. Think Gerald R. Ford class aircraft carrier going to space and back, with 5000 ton cargo capacity to LEO, or in that neighborhood. My math on a NTR Starship: (1 ton = 1000kg throughout) Two-stage Starship mass budget: 5000 tons, assuming max payload. Dry mass: 180 tons Current payload to LEO: 100 tons (my math says closer to 155t but whatever) Even if you assume that an NTR version would be more than 5x the dry mass (quite a bit more than your estimate) NTR mass budget (unchanged) 5000 tons NTR dry mass: 1000 tons Resulting payload to LEO: 800 tons Plus, the NTR equivalent would be SSTO, straight up and back, only the tankage needing a refill, possibly for years. Isp really matters a ton and it outweighs a lot of the admittedly significant concerns you raise. Same thrust, more than 5x the dry mass, and it's still enough to 8x the cargo. And of course this is without getting too sci-fi, no salt water Zubrin rockets or Project Orion or Project Pluto nonsense. SSTO using air as a working fluid until it gets up over ~30km is another nice concept.