I've been rereading this series, which I was obsessed with as a space-obsessed middle schooler. It's an uneven series, with the first two standing up well, and the third being pretty awful. This one, book four, was always my favorite. The book when the teenage astronauts are actually on their way to Mars in huge ships, full of science and big dreams and hormones and some incredibly silly personal problems. (Nathan almost kills himself trying to skateboard on the spinning, gravity-inducing hydroponics lab. Luckily he just breaks a leg, and his ego.) But there's adventure. And relatable characters. And an exciting near-disaster in space, which can only be solved with some solid logic and an unlikely friendship between a straight-laced German boy and a wild, rule-breaking Irish boy. There's a real internationalism embedded in this whole series, deliberately, with main characters from all over the world, including the Soviet Union. It's optimistic and anti-nationalist, with some lovely Star Trek vibes, imagining a world where it's possible to overcome national borders and hatred. At least for a global Mars mission. And it's also fun and hokey. A delightful read for 2025.