Comment by ggm

Could waste heat drive Stirling engines? Web says they were explored by NASA but also has a lot of yea... nah comments.

If there was an acceptable efficiency to concentrate the heat into mass, you wind up at ion engines and shed heat physically for thrust.

I think he hasn't done his sums, or maybe we need a "show your workings" moment over the Fermi numbers on this.

I'm sceptical.