What science fiction made space genuinely terrifying without using monsters or horror?
I'm looking for SF that makes space frightening just by treating it seriously.
Not because there's something hiding outside the airlock, but because you're surrounded by distances so huge they almost stop meaning anything, help might be months or years away, and one tiny mechanical failure can turn an ordinary situation into something completely hopeless.
I love when a book makes a functioning ship feel less like a safe little home travelling through space and more like an absurdly fragile bubble that has no business keeping humans alive out there.
The stuff that gets to me most is when nobody is even doing anything wrong. No evil corporation sabotaging the mission, no alien predator, no mysterious signal.
Maybe someone gets sick halfway between planets. Maybe a burn is slightly wrong and there's simply not enough fuel to correct it. Maybe two people can technically communicate but the delay is so long that having a conversation stops feeling like talking to another person.
That kind of thing scares me more than most actual horror because there's nothing to defeat. Physics isn't angry at you, it just doesn't care.
What books gave you that feeling?
Bonus points if they're not primarily marketed as horror. I'm less interested in "space contains a scary thing" and more in "space itself is an absolutely awful place for a human being to exist."