How NASA monitors satellites for collision avoidance

Ars Technica : Conjunction assessment (CA) is the jargonistic term for monitoring satellites and debris in orbit around Earth and identifying likely major collisions. NASA’s Goddard Space Flight Center began monitoring for potential collisions in 2004, and NASA formalized a policy in 2007: All hardware with maneuver capability in low Earth orbit (LEO) or geosynchronous Earth orbit (GEO) must have CA performed regularly. To do that, NASA partnered with the Department of Defense’s US Strategic Command , which tracks objects in Earth orbit as part of its missile launch detection and monitoring mission. Goddard’s CA system is now heavily automated. Downloads of updated tracking data are processed daily, with analyses of future paths run forward 7 days for LEO and 10 days for GEO. The system uses Matlab to perform two-dimensional, Monte Carlo, and nonlinear analyses to determine collision probabilities, which are flagged for monitoring. If a probability doesn’t decrease, the system can also calculate the necessary maneuvers to move the threatened satellite.