NASA had been working on mobile fission called the Prometheus reactor for the Jupiter Icy Moons Orbiter (JIMO) until cost overruns caused Congress to cancel the project in 2005. I was a huge fan of JIMO and when presenting at NASA HQ in 2019, I pitched a replacement at 1/10 the cost by shrinking the antenna systems. (JIMO boasted an impressive, 200kwe ice penetrating radar system). NIAC was interested but didn’t have access to the kind of cash needed for a phase 1 grant (what we were after. NIAC Phase 1 grants only very rarely exceed $150k, which is not enough to do what we proposed.)
NASA restarted their funding for nuclear 3 years ago? We may yet see nuclear electric, if for no other reason than that they need a reactor to build what they want on the Moon. Small Modular Reactors that generate on the order of 300MW electric are a thing terrestrially. GE has one small enough to fit on a tractor trailer (without cooling) and DoE has some nice high temperature radiators first pioneered for Prometheus, so it looks like given an operating Starship, NASA may get its Moonbase.
Fusion, as I said; scales with the 7th power of the confinement radius, so it is very hard to make work small. However, I think Eric Learner at Lawrenceville Plasma Physics in NJ is still working on his Dense Plasma Focus Fusion reactor. If that ever works, it’s small enough to build an aerospace fighter—really, tiny. That is super cool tech, boron fusion at many times hotter than the sun in a tiny plasmoid. It’s basically a special take on Robert Brussard’s a-neutronic Polywell reactor the US Navy still funds in secret. Cool tech that avoids the neutron flux issue Richard noted above. I wrote a white paper about it in 2003, encouraging federal funding, and DoE picked them up for a few years afterward. I really hope
that work continues. If Learner had 1/100 the funding of Star Citizen this last decade, there’s an excellent chance we’d have fusion powered launch vehicles and aerospace fighters.
I know the head of NASA’s Advanced Power and Propulsion, Dr. Dennis Bushnell; and I know he has thoroughly investigated Cold Fusion. He is not a believer, and those folks have had a lot of time to make their case. I doubt that is in the offering. I also know he fully investigated Brilliant Light and Power (formally “Black Light Power”), and found nothing there. Fact is there are a lot of places pretending they have these solutions, and billions waiting for investment. Despite BLP has had tens of millions in funding for decades, they never show the goods. It’s no wonder Dennis is habitually skeptical.