I'm impressed by the interweaving of theme and plot. It is very skillfully done. The theme of 'one for many' motivates the actions at the major plot points.

On the down side, the characters could have been done a bit better. The father, in particular, was wooden, and spoke like a sociology professor.

Also, the background was not well thought out. ( And this is where I lost the proverbial suspension of disbelief ) Who builds a spaceship - or anything that big - without thinking about maintenance? The examples are boundless: my car has ports where a computer can be plugged in. It also has a spare tire. The pony express had extra stations in case of a hobbled horse. Even the tunnel in Stalag 17 had a side cubby where spare parts were kept. Every military ship from frigates on up has a tool room.
I don't see a multi-kilometer object being build with no facilities for repair. It wouldn't take much: just a stash of extra air, food, water, and tools every few kilometers. Even if there are structural reasons why they could not be attached, the designers would have had something for maintenance, like a small one-man spaceship that could get to the furthest edge of the sail.
The sail is mission-critical. There have to be better planned maintenance facilities and procedures, or I don't believe the story.

I felt the story was well-written and impactful enough to suspend my disbelief for about a minute, but then I considered the below:

Dr. Hamilton: NOOOOOO! Why did he push off rather than use his remaining fuel to come closer so that we can arrange for someone to deliver enough air? He would have had considerably more than 72 hours of air left for his return trip which would have surely been slower than his sleepless initial trip - very likely sufficient time for someone to go and meet him at a midway point even if they are not as familiar with the pattern...

Yeah, it's a ridiculous premise. I can't imagine NASA launching any vessel without having a plan to fix minor structural damage sustained en route.