, but they wouldn’t use it if there was a significant chance of it harming the people on board.

This is spaceflight. There is always a tremendous chance of harm to people on board, even with speculative nuclear technology to get the spacecraft a little less like thin paper bags.

I would highly recommend reading up on Project Rho, on somewhat feasable near term technologies if we can just figure out the engineering: https://projectrho.com/public_html/rocket/

They're awesome, and I hope they get funded. But it will also dispell any illusuion you have of spaceflight being remotely practical on a large scale.