-dsr-

Since nobody else has mentioned it:

The (fictional) Ringworld is an immensely old mega-engineering project, requiring super-strength materials to put a habitable ring around a sunlike-star; a day-night cycle is provided by solar-collecting shadow squares in a smaller (thus faster-moving) orbit, connected by super-strength wire.

This is an unstable arrangement, and requires repeated adjustments every century or so. Naturally, that system broke down (via capitalists grabbing the expensive fusion power plants for their own purposes) and the backup system was destroyed by a bioengineered weapon.

The resolution to all this depends on psychic luck produced by evolutionary processes over the course of a handful of generations on Earth.

Truly, “hard SF” means that enough details have been given that you can be sure it won’t work.

This inspires the feeling of hating both sides of a fight and hoping that they do as much damage to each other as possible before it ends.