The Calculating Stars (Book 1 of the Lady Astronaut duology) by Mary Robinette Kowal

“So much about how Kowal structures Elma’s journey works, from her early days as a math whiz and the effect it had on her psyche, through her growth as a competent and confident professional. Equally lovely is the supportive and charming relationship between Nathaniel and Elma. You can’t help but root them both on.

The back third of The Calculating Stars is both intellectually and emotionally satisfying—and nicely sets up The Fated Sky, which is the second half of Elma’s story. Just one month after The Calculating Stars’ release, we’ll finally learn exactly how Elma got herself to Mars.” — Locus