Thorki astronauts AU?
Maybe they’re estranged brothers, who pursued the same dream of becoming an astronaut and, somehow, ended up as part of the same mission. No-one is happy about it - in space they will spend a lot of time in close proximity to one another. But maybe NASA is pressed for time, or they are the only two people right for the job?
Once in space, they get by mostly by ignoring one another. But then some kind of a catastrophe takes out the rest of their crew. So they are trapped, alone, drifting into the void with small hopes of salvation… And they are forced to set aside their differences if they hope to survive.
More importantly: incestuous UST + zero-gravity sex!