Lagrange Point 5
Novelette 8,132 words Recommended by 2 award/anthology sources
"After so many decades of humanity dreaming about the first expedition to Mars, who could have guessed that we would not get within thirty million miles of the place? We were approaching the Mars Lagrange Point 5, which trails sixty degrees behind the planet. The exact physics and mathematics of Lagrange points..."
Quasar links out; the story lives on Asimov's, where the author gets the click.