Who are the characters in the story "The Cold Equations," and what are their problems?

"The Cold Equations" by Tom Godwin is a futuristic story
set in space.  The story features only two main characters--Barton the pilot and a young
girl named Marilyn who is a stowaway on Barton's EDS (emergency dispatch ship).  While
the story references Marilyn's brother and parents and a group of humans stranded on a
far-away planet, Marilyn and Barton are the only characters actually in the scenes of
the story.

Barton is on his way to deliver life-saving
medicine to some men, and he has only enough fuel to get to the men's location with a
very specific weight on board his ship.  Because Marilyn has chosen to stowaway on board
the EDS (an action which she knows is prohibited), she places Barton in a very difficult
position.  He either has to "dump" her into space so that he can make it to the ill men,
or he and she will both die in space presumably along with the men waiting for the
medicine.  Godwin sets up a "lifeboat" situation and causes readers to think about the
idea of sacrificing one for the good of the whole. Marilyn, while wanting to live, comes
to realize the gravity of the situation she has put herself and Barton in, and
eventually goes to her death.