I've been aware of Mary Robinette Kowal, but not yet been drawn to any of her books. It seems now that this may have been a mistake. The Calculating Stars isn't a perfect book, but it's a good one. It's the kind of hard SF that we don't see much anymore. While I was disappointed to find that Kowal claims to "understand none of" the orbital equations in the book, she presents them credibly, and I wouldn't have doubted her ability had she not herself admitted the lack.
It took me a while to get into the book. While it starts well, it veers quickly into a kind of progressive Right Stuff atmosphere that put me off, even allowing for the period and pseudo-military context. Eventually, though, they get past that.
The book kicks off with a familiar concept - a Hammer of God-style meteorite strike. But that's really just to fork the timeline to an alternate reality. The rest of the book is a hopeful (or perhaps idealized) women's perspective on the space race that's a little more along the Stephen Baxter line (but with emotions). The narrator is perhaps a bit too much of a poly-math to be credible in the way the book seems to aim for, but is otherwise within the bounds of fiction. I had more trouble with the narrator's character, which I found inconsistent - sometimes brave and outspoken, sometimes quiet and unassuming - even allowing again for the period, and for the character's anxiety. The problem was compounded for me by central couple's domestic life - a marital union so blissful and devoid of tension as to strain credulity. Even when one of the couple does get a teense grouchy, they immediately and invariably apologize, and all is well again. Even in conditions of high strain, neither ever puts a foot wrong, and neither holds a grudge. That's a problem, because while the focus of the book is clearly on the narrator, Kowal makes her marriage an integral, central part of the story, and it can't really hold the weight. The book's also a little heavy on the soft-focus sex for my taste, but that's a quibble.
Overall, this is a well, written, credible hard SF look at an alternate history of the space race, and deserving of attention. I'll be interested in the next book in the series, and Ms. Kowal's other work.