The post-war era was a big one for science fiction. We had a lot of evidence that the world was going to blow itself to smithereens via the atom bomb, so paranoia was high. This was only made worse by the fact that the computer was on the rise, threatening to put everyone out of work. Chemistry was giving us new drugs, vaccinations, new fuels, and household chemicals that were at least a bit concerning. Science was everywhere, and most of it was threatening to kill us all, and if you can think of a better atmosphere for the new crop of science fiction authors to rise out of, I'd like to hear about it! SF magazines were growing in both number and length, and the paper back was a huge new thing. Of course, when you've got authors writing books and stories, they start to look towards Hollywood, and while movies were exploding into the B-picture and Technicolor masterpiece eras. But there were only so many movies to be made.
Of course, the 1950s saw the explosion of television. That was like having to produce a movie every week, and there were writers who were up to the tasks. From the early series like Tom Corbett: Space Cadet and Rocky Jones: Space Ranger, early science fiction television was fairly weak, predictable, and almost always targeted to young boys. As always happens, the kids who were influenced by those early series would end up changing television and science fiction forever. Twilight Zone would start the trend to smarter, more adult science fiction shows. Rod Serling brought his unique image of what science fiction could do on television, and it would influence everyone for decades.
And then came Star Trek.
To say Star Trek was the most important thing to ever happen to science fiction television wwould be a massive understatement. It took a very interesting path, appealing to both adults and kids, dealing with heavy issues in a way that didn't feel too heavy, and giving an idea of what a future might look like when we finally got over all the problems of the present. Even more than that, it also proved the television shows with cult followings can survive in syndication, can create massive fandoms of their own, and can change the way the television business works.
Every scifi television show of the late 1960s and early 1970s worked with Star Trek's themes, and the show never died, as it led to many successful follow-on series. By the time 1977 rolled around, Star Trek was feeling a bit hoky and old hay, which opened the door for Star Wars to take over. So many series began to pop up in the late 1970s and 80s taking advantage of the Star Wars love, including a few that used the setting of the films.
The 1980s saw a slow petering-out of SF shows, but then everything changed again when David Lynch and Mark Frost brought Twin Peaks to television, and that led to another massive change, as TV could be art, and that would take more than a decade to filter down to the mainstream. On the other end, as more networks began to pop-up, like Fox, UPN, and The WB, they all began to seek out Science fiction shows in an attempt to capture a rabid audience. The rise of original cable programming gave us some of the best scifi moving images of all-time.
Today, with the Marvel and DC comic universes on TV, masters like Joss Whedon and JJ Abrams working on series, and the ever-expanding number of sources for SF, we may be living in a golden age of science fiction television!