“Tau Zero” by Poul Anderson
review copyright © 2022 by Doug Reeder
The Bussard ramjet engine of a colony starship is damaged, and the crew can't turn safely turn it off. Time dilation hurtles them ever-further into the future. (Jet engines don't work like that, but it's an acceptable break from reality.)
The crew's various reactions to the unending stress are the heart of the book, but the number of characters makes them hard to remember. Characters hook up and split up, without showing any of the problems that tends to result. One of the stressors is a ban on having children — but no gay relationships are even hinted at (as usual even in fiction from the 1970s). The captain isolates himself to improve morale, but I wasn't convinced it would work out like it does.
This would work better cut down to a novella.