SPACE DEBRIS
The satellites we depend on for communication, navigation and environmental monitoring are under increasing threat from all the junk that’s up there in orbit with them. This includes derelict satellites and the rocket stages used to launch them, but if that was the extent of the problem there would be a manageably small number of objects to keep track of.
Unfortunately, those objects have a tendency to multiply, partly due to explosions caused by residual fuel and partly through collisions. Events like these can create thousands of smaller fragments, which due to their high speed and random orbits, pose at least as much risk as the original object.