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.
Working satellites are equipped with manoeuvring thrusters so they can be moved to a different orbit if it’s known that a piece of space debris is heading their way. With tens of thousands of objects large enough to cause serious problems, though, it’s no easy task to keep track of all of them. Yet that’s exactly what the space surveillance and tracking segment of the ESA’S Space Situational Awareness programme has to do. It employs a network of telescopes, radars and laser-ranging stations to detect and track objects, then processes the resulting data at ESA mission control in Darmstadt, Germany. The latter will issue an alert if evasive action is deemed necessary.
This system works well at the moment, but that won’t always be the case. If things carry on as they are, the space debris problem will get much worse in the future. The number of new satellites being launched is higher than it has ever been, while the number of fragmentary objects is increasing due to ongoing collisions. The worry is that the amount of space debris could reach a tipping point, beyond which there is a continuous cascade of self-generating collisions. Known as Kessler syndrome, this would render certain orbits unusable if it continued unchecked. For this reason the ESA is also considering methods for the active removal of space debris. Its Clearspace-1 mission, if it goes according to plan, will be the first in the world to remove a piece of space debris from orbit.