Try this idea...
On the planet Tethys human settlers were involuntary. They were mutants or mutant sympathizers judged to be disruptive to society's attempts to rebuild after the wars. However, once it looked likely that there was going to be another series of wars (and that the emergency government was never going away anyway) people volunteered to go to the space colonies. Mutants that had long been hidden went to the rocket bases to emigrate to the stars.
Tethys received less help from the Earth than the other colonies, On the other claw, they were far less
Supervised as well.
This is basically a Golden Age Sci Fi setting. There has been a nuclear war, the mutants were treated as a moral and spiritual pollution, as were those who defended the civil liberties of the mutants. So far so typical for a large number of Sci Fi narratives circa 1950-1960. The twist is that the mutants and their sympathizers have been sent to a space colony.
Assume that the general setting is Tech Level 7+2^. This is meant to represent the kind of tech they talk about in period Sci-Fi.
Another setting assumption is that Tethys is suitable for human habitation in the same way as the majority of "Class M" planets in an old
Star Trek: OS episode. You can eat the exotic fruit and if there were alien Space Babes around they could mate with humans and have healthy babies.
The war scare was justified. Earth is now dead. Earth's colonies are surviving, in a few generations, they might thrive. Tethys is the poorest and least populated of the colonies, but they aren't destitute.
There have been no new colonists from Earth to Tethys for three generations. Given that Tethys has lower background radiation than Earth, no new genetic damage is being done to the colonists. The normal course of events has been weeding out the more severe mutations. At least bigotry and violence aren't major sources of death.
Psionics are a major part of the setting. PCs can take one of the 25-point packages from
GURPS Psis with no
Unusual Background. GMs should limit how many points PCs place in Psi powers.
This is setting is a Sci-Fi Western set after a nuclear war. Like the 19th century American West this is a poorer more isolated version of the society these people left behind. There are a few university towns which have a full range of available technologies and services. But poverty and isolation created by underdeveloped transport systems mean the majority of the colonists live at lower Tech Levels.
Although as written, this setting had no aliens native to Tethys, having humanoid aliens of the
Star Trek type, i.e. humans that look odd, would fit the genre conventions.