Certain galactic trade union (the Blue) has a base on a distant planet, where they mine extremely rare unobtanium. They have set up anti-spacecraft cannons and essentially turned the planet into an impregnable fortress. Everything in range except Blue cargo ships gets pulverized. Their competitors (the Red) want to get their hands on the unobtanium and decide to put the planet under blockade (or siege, don't know which word is better). For that purpose, they build a megastructure around the planet, which works like this:
- It prevents Blue cargo ships (and everyone else) from landing on the planet or leaving it. This way the Blue can not trade unobtanium, and also life on the planet gets really harsh without outside help. The Red expect the Blue to surrender after some time.
- This "blockade" consists of large number of space stations positioned at regular intervals forming a ball around the planet, out of range of Blue cannons.
- These stations are not orbiting the planet. Instead, they are interconnected and held in place by tethers (tractor/repulsor beams of sorts), therefore forming a kind of dyson sphere. Thrusters are used occassionally to compensate for unwanted drift.
- Each station is heavily armed. Whenever something is about to pass the blockade, tethers are used to pull the closest station into range and then back, after destroying the offender. Sensors can pick up anything big enough to carry a sufficiently dangerous payload or significant amount of supplies.
- Whole thing is controlled by a computer. It also used to be inhabited by a large number of military personnel and engineers, but after a long time without any incident they have been made redundant. Now it is manned by only a few people, just in case.
- There are still life support systems available on every station. Tethers can be used by personnel to travel rapidly from station to station.
- Red cargo ship visits this contraption from time to time to replace personnel and bring some supplies. This does not happen too often, as this planet is quite far from civilization
This blockade has been going on for a long time, until the Blue managed to sabotage it somehow, without the Red noticing. The question is, how did they do it?
The Red are much smarter than I am. If you see any obvious flaws, please point them out, but assume the Red have solved them (unless they break this whole concept entirely).
The computer can not be directly hacked, but perhaps it can be outsmarted somehow.
Understand, that there is not much of anything on this planet (except unobtanium, which can not be used to manufacture weapons/ships/anything useful). The Blue are starving down there (metaphorically speaking), that is a crucial point of all this. They can not pull off anything too expensive (like swarms of missiles of bigger cannons). They have to be smart, brute force is not an option.