Dare Mighty Things (by Heather Kaczynski)

This is part of a series of two books; I didn't know that when I started reading it, but it was abundantly clear at the end (and really the last chapters when we realized we weren't going to get to the space part in this book).

Cassandra Gupta is recruited for a secret NASA program where she competes with 25 other young people for a spot on a secret mission. This book covers the training and testing they do on the candidates, and Cassandra's journey in trying to outlast the others and be the one selected in the end.

I enjoy speculative fiction grounded in science, so I enjoyed the milieu of the book, as well as the characters. I read this for the "book with an asexual and/or aromantic main character" and honestly her asexuality was barely addressed and not really relevant. I'm going to count it anyway but I'll still try to find a book where this is more central to the plot. 

The cliffhanger ending didn't work for me and I'm still deciding if I enjoyed it enough to read the next one.  I think I did?