> A nuclear first stage launching from inside your biosphere is not a great idea I disagree. There are nuclear rocket designs that don't have radioactive exhau

> A nuclear first stage launching from inside your biosphere is not a great idea I disagree. There are nuclear rocket designs that don't have radioactive exhaust. Sure, its a little bit of a problem if it explodes, but not to bad. And actually if you do that, then you are much better set up for deep space exploration. > and making nuclear rockets reusable is harder than making chemical rockets reusable Not sure that is actually true. I don't see a reason why something like a NERVA engine should be just as reusable as any chemical engine. We have way to much fear of radiation. We should be already living in the nuclear age. Given that NERVA was a 1960 engine I don't think that answer works for Fermi, specially given how many more smaller planets there are (we just have not found them).