I am trying to find a book of short science fiction stories that contains a short story about an astronaut crew that land on a moon or planet and one astronaut on an EVA (spacewalk) on the surface discovers a crew of three aliens next to a crashed ship. One of them injured. He sends them back to his ship sacrificing his spot aboard for them. I believe the story is called "The Samaritan".
It sounds like The Samaritan by Richard Harper. The short story originally appeared in the Feb. 1963 issue of Boys' Life, but has appeared in several subsequent anthologies. A bibiography is available on isfdb.