Space debris

Space debris includes all non-functional, human-made objects in space, from entire defunct satellites to tiny paint flecks. The primary sources are spent rocket stages, abandoned satellites, explosion fragments, and debris from collisions. For example, the 2009 Iridium–Cosmos collision alone generated thousands of trackable fragments.¹ Additionally, anti-satellite tests, such as China's 2007 ASAT test, have contributed significantly to the debris population.² Even operational activities, like the release of lens caps or bolts, add to the problem.

Debris poses a collision hazard to active satellites and crewed spacecraft, with impacts at orbital velocities exceeding 10 km/s capable of catastrophic damage. The International Space Station performs periodic debris avoidance maneuvers to mitigate risk.³ Mitigation measures include design-for-demise, passivation of upper stages, and post-mission disposal into graveyard orbits or controlled reentry. The Inter-Agency Space Debris Coordination Committee (IADC) has established guidelines adopted by many nations.⁴ However, even with perfect compliance, the existing debris population will continue to collide, leading to the Kessler syndrome scenario.

Ground-based radar and optical telescopes track debris larger than about 10 cm in low Earth orbit, while smaller objects are statistically modeled. NASA's Orbital Debris Program Office and the European Space Agency's Space Debris Office maintain models and databases.⁵ Research focuses on characterizing the debris environment and predicting future growth. In 2024, ESA's DRACO mission was approved to demonstrate active debris removal by capturing and deorbiting a target object. Such missions are critical because natural decay can take decades or centuries at higher altitudes.

Beyond the well-known hazards, space debris has surprising facets. For instance, the oldest debris still in orbit is the Vanguard 1 satellite, launched in 1958, which remains as a test of long-term orbital stability.⁶ Also, debris can become a scientific tool: the Long Duration Exposure Facility (LDEF) was retrieved to study micrometeoroid and debris impacts. Furthermore, some debris has cultural significance, such as the Tesla Roadster launched by SpaceX in 2018, which is technically a defunct object but not typically counted as debris. The legal status of debris is also complex, with the Outer Space Treaty assigning liability to the launching state, but no binding rules for removal exist.⁷

Kessler syndrome

A runaway cascade of collisions where each collision creates more debris, leading to an exponential increase in collision risk.

Passivation

The process of removing residual energy (e.g., fuel, batteries) from a spacecraft at end of mission to prevent explosions.

Graveyard orbit

A high-altitude orbit used for disposal of geostationary satellites to reduce collision risk with active ones.