Obviously technology will improve, and must improve or we would have colonized off world places more often already. However, once we start to pull new technologies out of a hat,
I have not pulled any technologies out of a hat. I avoided doing that in the above analysis. I have not speculated much and not proposed anything that is physically impossible. Everything I cite has been proposed and discussed in detail by experts at places like NASA. Other than cold fusoin, most of what I discuss is a straightforward extrapolation of existing technology. The space elevator is a good example. It cannot be made now, but it is within reach. It violates no laws of physics.
Conditions on Mars are now known in great detail thanks to the Martian explorer robots. The weather there and the hazards are well understood. We know that people can survive in space, because they have -- in the space station. We know that robots can "withstand a large temperature interval, it must be impervious to dust and various kinds of radiation" because they do that already, in space telescopes and on Mars. The make-up of asteroids is less well known, but we know that they have a great deal of precious materials, and we know approximately how many there are.
We know that mining in 20 years or 50 years will be almost all be done by robots, because it is already, in first-world mines. The trucks drive themselves. The excavators are mostly automatic and they take only one person, replacing hundreds of people.
People won't probably be beamed to Mars, etc, but maybe they will. (Star Trek used beaming people to places as a device to eliminate television
Obviously that is impossible as far as anyone knows. Nothing like it on any scale has been accomplished, unless you count quantum cryptography and spooky action at a distance. Which, I suppose you might count, but the scale is different.
I did not include antigravity in the discussion. If we had it, LEO access and planetary exploration would be a cinch. We could do it on an industrial scale in ten years! It would be great, but as far as I know antigravity machines are impossible.
I find discussion like this more interesting when you stick to known technology and near-term extrapolation. I do not even bet heavily on helium-3, because the experts dispute how much there is available on the moon, and how well a helium-3 reactor might work. Many of them say it is promising, so it should be noted.
Okay, I did let myself go, here:
"If you could assemble elements, it would be nifty to build a Dyson sphere, capture solar wind, transmute it, and use it to assemble entire planets. That's thinking big! That would be a handy material to make the sphere itself out of, since it happens to be headed out in all directions anyway."
Ya' gotta love Dyson spheres! Every solar system should have one.