Earlier this week, Progress 89, an uncrewed Russian supply ship docked at the International Space Station, used a 5-minute and 31-second burn to move the ISS to a higher orbit. According to a joint statement, the maneuver was undertaken to ensure the station would avoid a collision with the remains of a "defunct defense meteorological satellite."
Orbital space debris consists of defunct satellites, discarded rocket parts, and other space junk, which poses an enormous threat to the ISS. Since entering low Earth orbit in 1998, the station has adjusted its position dozens of times. The European Space Agency estimates that there are 29,000 pieces of space debris larger than 10cm in orbit, 670,000 larger than 1 cm, and more than 170 million larger than 1mm.
Any of these objects can cause harm to an operational spacecraft. For example, a collision with a 10-cm object would entail a catastrophic fragmentation of a typical satellite, a 1-cm object would most likely disable a spacecraft and penetrate the ISS shields, and a 1-mm object could destroy sub-systems on board a spacecraft. Scientists generally agree that, for typical satellites, a collision with an energy-to-mass ratio exceeding 40 J/g would be catastrophic.
As more debris enters low Earth orbit, some scientists are concerned about Kessler Syndrome. This situation occurs when the amount of debris causes a cascade of collisions, which results in more debris and more collisions. In the worst-case scenario, the Kessler Syndrome theory predicts that the Earth's orbit would become filled with debris, making it unusable for satellites or spacecraft. The details of Kessler Syndrome are much debated in the scientific community, but there is near universal agreement that tracking alone is insufficient and further measures are necessary to reduce the amount of debris in orbit.
Previously: The answer to space junk is space lasers
