[officemonkey]

There used to be steam-powered and battery-powered cars in the early 20th Century. There was an Edison-Westinghouse war in electricity distribution.

Typically, a consensus is reached based on technical and economic limitations.

For example, nuclear-powered aircraft? You need shielding to protect the human crew. You also need a reactor that can survive a crash. That's why they use nuclear fuel for unmanned probes. There are no humans to protect, and it's a one-way trip.

[catalogia]

It's my understanding that if not for the development of ICBMs, the US might have created cruise missiles powered by unshielded nuclear reactors. They got as far as running a prototype engine for five minutes, but the whole project became pointless when it became clear ICBMs would work.

https://en.wikipedia.org/wiki/Project_Pluto

Russia has seemingly been developing this same sort of technology in recent years. Presumably this is in response to anti-ballistic missile technology calling into question the future effectiveness of ICBMs.

https://en.wikipedia.org/wiki/9M730_Burevestnik

[acidburnNSA]

Shielding is all probably doable, but still really hard and questionable. Here's a good chapter on the Human Factors of Nuclear Powered Flight: https://babel.hathitrust.org/cgi/pt?id=mdp.39015001555146&vi...