Comment by Ukv

> your ship needs to be repaired on the way, do you need to have repair tools, materials, for that on board ? Seafaring cargo ship can not be going 100 years without repair. I bet space ship can not go either.

Seems clear that yes, you would take tools and materials to allow for repairs, along with redundancies for any essential systems. If "your 3d printer on board which makes your repair tools brakes" you'd fix it using tools you already have available or printed out from one of your other 3D printers (even the ISS, far closer to Earth, has multiple).

It's true that creating, launching, and maintaining a generational ship would be a massive engineering undertaking, and underestimating the level of redundancy/repairs needed for some system could be what ends up causing a catastrophic issue, but the idea that we'd take zero tools for maintenance, expecting no repairs to be made at all, feels a frivolous reason to rule out generational ships.