> Well, so is building Dyson swarms and spheres Building a Dyson Swarm, which is really just the problem of creating one self-sustaining orbital (since after t

> Well, so is building Dyson swarms and spheres Building a Dyson Swarm, which is really just the problem of creating one self-sustaining orbital (since after that it's just a scaling issue) is really just an engineering problem. A huge one of course but we already have teh technology to create a material as strong as stainless steel and to build solar power collectors. Currently, the big cost is getting material into space. LEO payloads are still (AFAIK) >$1000/kg. Getting that to $100/kg or even $10/kg completely changes that equation and yes, there are viable paths to reach that (eg orbital rings). Fusion isn't even an engineering problem yet: it's a science problem. The big problem is energy loss from neutrons (as well as those neutrons destroying your reactor). That's not a problem for stars. They have gravity and are simply so large that the vast majority of neutrons are captured and feed into the overall process. It's not clear we'll ever reasonably solve these problems. A fusion reactor is large and expensive and has many moving parts since, ultimately, we just use heat to turn a turbine in the same way a coal or NG plant does. Plus it needs fuel. Over long timescales that's still a problem. What fuel? Helium-3 (for so-called aneutronic fusion) is a big problem to source. Deuterium is easy to get. Tritium is harder to get. Protium is obviously easy to get. Nuclear power as it currently stands on EArth cannot compete with the cost of solar power with solar panel efficiency still going up. What happens to that when you put that solar panel in space and now it's producing ~7 times as much power since day/night and weather are no longer factors and there's no energy loss to the atmosphere? This is why I say "if" nuclear fusion will ever be economically viable. I'm not saying it won't be but there are massive hurdles to even theoretical economic nuclear fusion.