How does the ISS protect itself against space debris?
The International Space Station has debris shields deployed around the manned modules. These shields are composed of two metal sheets, separated by about 10 cm. The outer ‘bumper’ shield exploits the impact energy to shatter the debris object, such that the inner ‘back wall’ can withstand the resulting spray of smaller-sized fragments. Between the walls, fabric with the same functionality as in bullet-proof vests is deployed; this design enables the shield to defeat debris objects up to 1 cm in size. For debris objects that are large enough to be contained in the US Space Surveillance catalogue, one can predict their orbits and compare them with the ISS orbit to determine close approaches. Assuming that the determination accuracy of both orbits is known, then a given fly-by distance can be translated into an in-orbit collision risk. If such a risk exceeds the ISS threshold level, then the Space Station performs an avoidance manoeuvre. The ISS performed seven of these manoeuvres by mid-
