PS: the nutshell on nuclear-thermal engines is that it allows you to finally break the "tyranny of the rocket equation".

Right now the reason space travel sucks is staging. To send a small ship to mars, you need a small rocket. But you have to inject that small rocket into orbit with a medium rocket. And you have to get that medium rocket out of the atmosphere with a large rocket. At each stage, the only way you can gain forward speed is by throwing an equal mass backwards (not quite but works for a description). So to throw a tiny mass where you want it, you need to throw a whole bunch of crap away first to push you. The Saturn-V rocket was more than 90% fuel by weight. Chemical rockets are literally just big gas tanks that you can drop part of when they're empty so you don't have to drag around dead weight, that's it.

Working temperature is an extremely important factor for the specific impulse (thrust per mass of fuel consumed) a rocket generates. The hotter the reaction mass, the more thrust you get out of it. I'll come back to this but the point is you need to heat the gas.

In chemical rockets the energy source and the reaction mass are integral, you burn the fuel and it uses its hot exhaust as a reaction mass. The advantage of a nuclear-thermal engine is that they're separate - with fission/fusion you can heat an immense amount of reaction mass with a small amount of fuel, and you can pick up more reaction mass as you go (via ramscoop). Suddenly the whole picture changes, because you no longer need to lift the skyscraper full of reaction mass that you don't really care about in order to move the tiny spacecraft you do want. As long as you're going fast enough you can ramscoop yourself more from hydrogen that's just floating around space at about 1 atom per cm^3.

Not only that but nuclear rockets get much hotter than chemical rockets and you could produce about twice the specific impulse, making your reaction mass go a lot farther.

Obviously the task of building orbital infrastructure is an immense one. It's a 50-year project, maybe a little less if we pipeline things to push it along. There is a massive amount of R&D that would have to happen, but almost all of the technology described here literally exists today. There are no magic materials we need to invent, it's just engineering the pieces together. We have linear induction motors, we have externally-stabilized supertall structures (antenna towers), we have steam catapults, we have nuclear reactors. We just need to turn them into a launch loop. And you don't even need all that launch capacity, it just makes things easier - Deep Space Industries wants to pull an asteroid in with just small probes, it's just going to take a lot, lot longer. NASA has tested nuclear rockets (NERVA program). etc etc. We would have some work to do on implementing a practical ramscoop, and we would need to figure out how to do mining, refining, and fabrication effectively, but those are relatively discrete tasks that are solvable with current technology, it's just a matter of figuring out what works and what doesn't.

Our children could live in an interplanetary (bordering on interstellar) society if we wanted them to, using shit we've got lying around right now. Our children could walk on other planets and work in space. They could live to see the first pictures beamed back from another solar system, and if not them then their children would.

Throughout history humans have looked up at the stars and wondered what was going on up there. They watched the gods wander the sky, and made up tales of what they might be doing. The truth is that we are a unique generation of human beings, because we are the first humans to ever live who have had the planets and the stars in their grasp and yet turned away. The Greatest Generation didn't. It's really only in the last 20-30 years that we have lost our way, but now it's just perceived as normal. Like the grandparent said - a mission to Mars is just some impossible fantasy that's always 20 years away. The truth is that it's 20 years away because we never bothered to get started. It's the pile of dishes in our sink that we never wash, or the "check engine" light we always ignore. It's always easier to put it off until tomorrow. We're just so busy with [crisis of the day], or the standoff with [enemy of the day], or if there's no crisis then taxes need to be cut and there's just no money left in the budget to spare.

I don't particularly care that the moon landings were done out of a sense of nationalistic dick-waving. We don't refuse to drive on the interstates just because they were built so the military could move troops around during World War 3. We don't refuse to use the Internet just because it was designed as a military command-and-control system. We don't refuse to use computers because they were designed to break military codes and simulate the wing flutter of bomber aircraft and the explosions of nuclear warheads. The history of technological advancement is literally bathed in blood. I don't know for sure but I imagine the first tool humanity ever invented was used to bash someone's head in. The fact that we can reflect on that is the self-awareness we need to come together and make this push for our species' future.