I'm trying to remember the name of a story I've read- I can't remember if it was a book or a short story, but I suspect the latter. The part I'm remembering is set on a space ship powered by a solar sail. The solar sail is damaged, and one of the characters is sent out to fix it. I think they were the engineer that designed it, so they were the only one familiar enough with the structure to travel across it quickly & safely. As they're travelling across the sail, I think their suit is damaged, and they start slowly losing oxygen. The whole trip took several days, and it was urgent, so the character didn't have time to sleep. One of the other characters is constantly talking to them, trying to keep them awake. Between the lack of sleep and loss of oxygen, they begin hallucinating. In the end, they managed to patch the hole in the solar sail, but don't have enough oxygen to make it back.
This sounds like Mono no aware by Ken Liu.
From a review:
In short, what’s left of humanity – slightly more than a thousand individuals – is traveling on a solar-sail-powered ship toward a new home: Earth found itself on the path of a huge asteroid, and is no more. Main character Hiroto alternates details from shipboard life with memories of his childhood at the time in which the Hammer, that’s the name given to the asteroid, was nearing Earth and the evacuation of its people was underway. There is a sharp dichotomy between the events of the past and Hiroto’s quiet acceptance of what happened, of the tragedy that caused the whole of humanity to be reduced to the present scant handful, and it’s not because of the emotional removal, but thanks to the lucid awareness that to behave otherwise would be useless, that survival depends on the ability to rise above one’s personal needs, to care about “the web of relationships in which we’re enmeshed”, as Hiroto’s father used to advise him.
When a tear in the solar sail threatens to send their ship, the Hope, wildly off-course, it will be Hiroto’s job to step in and make sure that what future still is there for humanity will reach its fruition, and his choices will be determined by the meaning of the phrase that’s this story’s title, a complex concept that can have several meanings, the most important one being that all things in life are temporary, that everything passes: what matters is not so much an individual’s life, but rather “the places we hold in the web of others’ lives”.
It's available to read at https://www.lightspeedmagazine.com/fiction/mono-no-aware/.