I actually wrote the story for my last writers' workshop in my (Seton Hill University!) M.F.A. progam. I did set out with the perverse goal of initially tricking the reader into thinking the protagonist was unsympathetic--when in reality she was on a mission to save the world. An additional challenge I gave myself was to have the protagonist not actually do anything, but hopefully have the reader still empathize with her in the end. I do think this is a somewhat unexplored topic in SF: What happens to all those intrepid world-savers when their missions fail or they are unable to complete them?
So, notice, I attempted to write a story fraught with less-common ideas/concepts.
Workshopping the story was interesting. Many in the group didn't like it too much. But, I did get many helpful comments which helped to make the story better. (Thank you, workshoppers for your help! I appreciate it.)
The tale of this tale points to a very important point: writers need input from other writers. :)
Good luck finding your perfect critiquers/workshoppers!
I'd like to point out an additional factor in my success here: perseverance. I submitted this story to several markets unsuccessfully. But I believed in it so I kept on plugging, despite rejection after rejection. Writing is difficult, but selling can be even more difficult.
Good luck with your selling efforts!