system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How has the ISS managed to stay in orbit for over 20 years and not be obliterated by random space junk moving faster than a bullet?

Is it just pure luck? Or is there some sort of mechanism or system in place to divert or destroy the junk before impact?
gpt
At orbital speed, any small object will just immediately disintegrate on impact rather than stay intact and penetrate like a bullet. That means that it is enough to have two or more layers between space and the crew - a collision might punch a hole through the outer layer, but probably not through the second because all its momentum is spread out over a larger area. 

But if any large object hits the ISS, it might destroy the entire thing and kill its crew. For that reason, they track space debris with radar, and if it is estimated that it will pass the ISS (or any other satellite) too close for comfort, they will use their thrusters for evasive maneuvers. 

In addition to that, at the altitude that the ISS is orbiting, there is still a very thin atmosphere. Anything flying up there is slowing down and will eventually fall back to earth. Which means that the ISS has to use its thrusters anyway to maintain its altitude, which can be combined with evasive maneuvers. It also means that debris at that altitude cleans itself up after a while.

Debris is a much greater problem at higher altitude, above 500 km. There, the atmosphere is so thin that all that junk will basically stay there forever.