The November 2019 issue of Prism (published by ASEE) includes an article by Thomas Grose about the risks associated with space junk in low earth orbit (LEO). The likelihood of a collision continues to increase: 4000 satellites and the International Space Station (ISS) travel in LEO, which has 128 million bits of junk; 20,000 pieces have a diameter greater than 10 cm. The consequences of a collision could be more debris, a damaged satellite (which could interrupt communication or other services), or a casualty on the ISS. A possible worst case is the Kessler syndrome (a chain reaction of debris-generating collisions).
The current mitigation efforts include rules to reduce the growth of space junk and a system for detecting possible collisions (so that spacecraft can be moved out of the way). NASA has a technical standard, "Process for Limiting Orbital Debris," that requires space programs to assess and limit the likelihood of generating debris during normal operations, explosions, intentional breakups, and collisions. "Orbital debris" is defined as follows:
Artificial objects, including derelict spacecraft and spent launch vehicle orbital stages, left in orbit which no longer serve a useful purpose. In this document, only debris of diameter 1 mm and larger is considered.The NASA standard also discusses reducing the likelihood of collision by reducing a spacecraft's cross-sectional area.
New systems for tracking more space junk more precisely (e.g., the Space Fence) could lead to an automated "traffic control" system that warns a spacecraft operator when a collision is imminent while reducing the likelihood of false alarms. An alarm is costly because it disrupts normal operations, and the spacecraft must burn fuel to move away from the space junk and then return to its normal position.
Researchers are also developing spacecraft that can capture space junk, which could reduce the likelihood of a collision.
The article mentions few efforts to reduce the consequences of a collision. Astronauts in the ISS can head to a shelter if a close call is imminent. But hardening a satellite would require more mass, which makes it more expensive. Perhaps we need "shatterproof" materials or designs for spacecraft.
