The future has less power than expected. From the beginnings of the industrial revolution up to the first oil crisis, new energy sources were discovered, exploited, and scaled up. Space travel requires insanely high power levels, and it was assumed back in the 1950s that those were coming. They weren't. In the last 50 years, there have been no new power sources. We're still mostly on oil, coal, natural gas, and hydro…
So from just your comment, my take is different - essentially, nuclear power was demonized, mismanaged and ignored. We have the technology to have an abundance of terrestrial power to do most things if we'd only embrace nuclear power. Look at Philae - because it didn't contain a fission source, it's stuck without the capability to replenish it's power source. What would have happened if we weren't scared to death of…
So embracing nuclear power is a bit harder than it may seem from a technological point of view. Also, since we can currently only use fission, shielding will always lead to nuclear power being almost exclusively used for heavy stationary projects or at best something that floats such as a very large nuclear powered boat. In those cases the weight isn't a huge factor.