Tau zero
Poul Anderson is a writer's writer, David Brin, Vernor Vinge and others swear by him and Vinge even dedicated his epic [b:A Deepness in the Sky|226004|A Deepness in the Sky (Zones of Thought #2)|Vernor Vinge|https://d.gr-assets.com/books/1217218691s/226004.jpg|1270006] to him. His influence on their work is fairly obvious, Anderson knew his science and was able to employ that knowledge to max effect in his fiction. He was also a natural story teller who never neglected the human element in his sf stories.
Tau Zero is - I believe - what veteran sf readers would call
"diamond hard sf" where all the fictional science is completely plausible. So no teleportation, snarky robots, or little green men. I have to admit a lot of the "interstellar astronautics theory" and other scientific details went whoosh! right over my head, yet somehow Anderson always ensured that the story is never incomprehensible. I also learned a lot about time dilation and relativity that I never knew before, which will undoubtedly make me the life of the next party I go to.
The characters are fairly interesting people, led by a protagonist who is a "pragmatism personified" super stoic constable, but at least he is very articulate, not one of those cliche taciturn hero type. In any case, given the short length of the novel (190 pages) there is not all that much room to develop the characters, a lot of them seem to be defined by their personal quirks.
For some reason this book reminds me of David Bowie's
"Space Oddity", not in specifics, as the story follows an entire starship crew not just one Major Tom. However, there is a sense of that
"Planet Earth is blue and there's nothing I can do" sort of loneliness and hopelessness among the crew through out most of the novel. Even before the starship went out of control the crew never had any hope of returning home to the people they know due to the time dilation effect. After things go "pear-shaped" the damned thing can no longer decelerate let alone stop, heading to goodness knows where. The final destination turned out to be truly awesome.
A lot of people who ask for sf book recommendations (in Reddit especially) tend to stipulate that they don't want anything pre-70s, or even pre-80s due to the misconception that old sf books are "outdated". Their prerogative of course but it is a shame that they will miss out on older gems like this one.
Now go take your protein pills and put your helmet on.