This was very enjoyable sci-fi that wasn't quite as "hard" as it thought it was. The author consulted with NASA and gave a pretty good look at what long term space travel would be like, but some issues were pure magic or were handwaved. I agree with one of the prominent reviews here that there was no story reason for the characters to be 17 years old.

Making this a US/Soviet retro-futuristic conflict was an interesting choice that I'm thinking over.

Choosing the name "Cusk" was unfortunate.

This was good enough that I'll read the sequel when it comes out, but I wonder where the sequel can go. This is a pretty closed loop of a story. Seems difficult to come up with a new mystery for the next book.

Also, if you're going to have sex on a spacecraft, and there's a zero G area, you're going to try it in the zero G area at least once.