A good (if somewhat dated) read is “The Third Industrial Revolution” by B. Harry Stine. There are all sorts of things which can be done very profitably in space.
Once you are in orbit it makes sense to dust off the pebble bed NERVA engine which we successfully tested in 1971.
It was about the size of a 55 gal. drum and produced about 5 GIGAWATTS of power, IIRC. It is a fission reactor with the fuel contained in ceramic “pebbles”. Fission reaction products are contained in the pebbles.
Using liquid H2 as the fuel, you can get a specific impulse of over 900 seconds vs. 460 sec. for H2/O2 reaction. For you non-aerospace engineers, that improvement in specific impulse is HUGE because of MV2.
That means you can make a ship that can go ANYWHERE in the Solar System in months. You can land such a ship on Luna, Mars, or Mercury and take off again. You can get to Jupiter’s moons in months instead of years.
That’s why a source of hydrogen in orbit is so important. A carbonaceous chondrite asteroid is loaded with water.
BTW, this concept has been around since at least the early 1950s when they did the calculations with slide rules.
We stand on the shoulders of giants.