What Are the Risks?
Orbital debris generally moves at very high speeds relative to operational satellites. In low Earth orbit (altitudes lower than 2,000 km) the average relative velocity at impact is 10 km/sec (36,000 km/hr or 21,600 mph). At this velocity, even small particles contain significant amounts of kinetic energy. For example, NASA frequently replaced space shuttle orbiter windows because they were significantly damaged by objects as small as a flake of paint. An aluminum sphere 1.3 mm in diameter has damage potential similar to that of a .22-caliber long rifle bullet. The energy of an aluminum sphere 1 cm in diameter is comparable to a 400-lb safe traveling at 60 mph. A fragment 10-cm long is roughly comparable to 25 sticks of dynamite.
Debris particulates smaller than 1 mm in size do not generally pose a hazard to spacecraft functionality. However, they can erode sensitive surfaces such as optics and solar arrays. While the spacecraft may survive, degradation of certain components can still result in inability to complete the mission.
Debris fragments from 1 mm to 1 cm in size may or may not penetrate a spacecraft, depending on material selection and whether shielding is used. Penetration through a critical component, such as the flight computer or propellant tank, however, would result in loss of the spacecraft.
Debris fragments between 1 and 10 cm in size will penetrate and damage most spacecraft. If the spacecraft bus is impacted, satellite function will be terminated and, at the same time, a significant amount of small debris will be created. In large satellite constellations, this can lead to amplification of the local smaller debris population and its associated erosional effect.
If a 10-cm debris fragment weighing 1 kg collides with a typical 1,200-kg spacecraft bus, over one million fragments 1 mm in size and larger can be created. This collision results in formation of a debris cloud, which poses a magnified impact risk to any other spacecraft in the orbital vicinity (e.g., other constellation members).
At geosynchronous altitude, average relative velocity at impact is much lower than in low Earth orbit, about 200 m/sec (720 km/hr or 432 mph). This is because most objects in the geosynchronous ring move along similar orbits. Nevertheless, fragments at this velocity can still cause considerable damage upon impact. A 10-cm fragment in geosynchronous orbit has roughly the same damage potential as a 1-cm fragment in low Earth orbit. A 1-cm geosynchronous fragment is roughly equivalent to a 1-mm low Earth orbit fragment.