The International Space Station (ISS) was forced for an urgent change of orbit on November 11. This was to manoeuvre out of the way of a potential collision with space junk. The space junk was a piece of debris from the defunct Fengyun-1C weather satellite, destroyed in 2007 by a Chinese anti-satellite missile test. The satellite exploded into more than 3,500 pieces of debris, most of which are still orbiting. Many have now fallen into the ISS’s orbital region.
In the 23-year orbital lifetime of the ISS here have been about 30 close encounters with orbital debris requiring evasive action. Three of these near-misses occurred in 2020. In May this year there was a hit: a tiny piece of space junk punched a 5mm hole in the ISS’s Canadian-built robot arm.
To avoid the collision, a Russian Progress supply spacecraft docked to the station fired its rockets for just over six minutes. This changed the ISS’s speed by 0.7 metres per second and raised its orbit, already more than 400km high, by about 1.2km. As the largest inhabited space station, the ISS is the most vulnerable target. It orbits at 7.66 kilometres a second, fast enough to travel from Perth to Brisbane in under eight minutes.
A collision with even a small piece of debris could produce serious damage. What counts is the relative speed of the satellite and the junk, so some collisions could be slower while others could be faster and do even more damage.
The ISS modules are somewhat protected by multi-layer shielding to lessen the probability of a puncture and depressurisation. But there remains a risk that such an event could occur before the ISS reaches the end of its lifetime around the end of the decade.
No one has the technology to track every piece of debris. But possible methods for removing larger pieces from orbit are being investigated.