The Lady Astronaut of Mars — Mary Robinette Kowal

Thirty years ago, Elma York led the expedition that paved the way to life on Mars. For years she's been longing to go back up there, to once more explore the stars. But there are few opportunities for an aging astronaut, even the famous Lady Astronaut of Mars. When her chance finally comes, it may be too late. Elma must decide whether to stay with her sickening husband in what will surely be the final years of his life, or to have her final adventure and plunge deeper into the well of space.