I remember a short story from the early 1970s. I think it was in a “best science fiction stories for Boy Scouts,” but being 40 years ago, I may be wrong.
Anyways, the story goes that a scout ship is out on the fringe of the galaxy when they get an SOS call from a nearby planet. However, they are the only ship in the area. After landing, they send the captain who, by rotation, is the designated explorer. The planet is fully dark (no sun). He finds a wrecked ship with two survivors, one of whom is badly injured. He sends the two back with his return beacon, knowing it will leave him stranded alone on the planet. However, it gives humanity a chance to find another resident of the galaxy.