Time for the Stars, by Robert A. Heinlein
The second juvenile novel in this Infinite Possibilities book was fine, though not as good as Tunnel in the Sky. Citizen of the Galaxy is the last one and I'm not super-optimistic about it, but I might read it anyway; we'll see. After all, I was at the used bookstore today and got two vintage sci-fi paperbacks to read!
Again we have a massively overpopulated future, but this time there are severe taxes on extra children and they're looking for planets to colonize. Without anything better than near-light-speed travel, it's going to take a long time to find anything, but there is one big help; it turns out that pairs of twins can often be trained to communicate telepathically. So one twin can stay home and report what the traveling twin sees, and any good planets can be reported immediately.
Tom and his twin Pat are chosen to go, and Tom kind of resents that Pat, the dominant twin, has just assumed that he will be the one to go into space. But Pat's skiing accident puts Tom in the spaceship instead. Tom spends just four years helping to explore space, while Pat lives a long life at home. The ship finds a pretty good planet, but then a delayed consequence strikes. The next inhabitable planet is a real disaster. Tom is really wondering whether they should continue the trip.
A lot of this story is given over to Tom and Pat's relationship and Tom's work on figuring out his feelings about his kind of jerky brother. As a result, most of the other characters and relationships on board are not as fully described, except for the really wonderful Uncle Alfred. There is also quite a bit about the twin telepathy and life on board a closed spaceship. The planet adventures come off as side quests, really.
It's a decent read, nothing wrong with it, but it isn't one of the greats.