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Orbital debris, also referred to as “space debris” and “space junk,” includes both natural meteoroid and human-made debris in orbit around the Earth. Most orbital debris comprises human-made objects that no longer serves a useful function, such as pieces of spacecraft, tiny flecks of paint from a spacecraft, parts of rockets, satellites that are no longer working, or fragments resulting from explosions of objects in orbit.
As of May 4, 2022, there are 25,209 orbital spacecraft and orbital debris objects, collectively referred to as cataloged objects, that are tracked by the Department of Defense's global Space Surveillance Network (SSN) sensors. 16,651 of those catalogued objects – more than 66% – are classified as orbital debris. Much more debris exists which is too small to be tracked, but large enough to threaten human spaceflight and satellites.
The following chart shows the rapidly growing number of catalogued objects in space by orbit. Low Earth Orbit (LEO), which is considered to be an Earth-centric orbit with an altitude of 2000 km or below, is the most congested and is exhibiting the highest growth in cataloged space objects.
The chart below shows the growth of cataloged objects in LEO based on orbital altitude. It also shows that some orbital altitudes such as between 400 and 1,000 km have significantly more catalogued objects than other altitudes.
The History of Orbital Debris Creation
Since the beginning of the space age, there have been more than 550 confirmed “fragmentation events” in Earth orbit, each event generating new orbital debris. Such events have various causes, and some are responsible for creating far greater quantities of debris than others. Notably, the deliberate destruction of the Chinese Fengyun-1C spacecraft in 2007 and the accidental collision of an American and a Russian spacecraft in 2009 increased the tracked orbital debris population in LEO by approximately 70%.
The causes of fragmentation events and frequency of occurrence as of December 2020 are provided below:
PROPULSION – 39.52% Energy left undisposed of on-board a satellite or rocket body can lead to accidental explosions, for example due to heat stress.
DELIBERATE – 23.77% All intentional breakup events, e.g. satellites designed to explode if atmospheric re-entry went wrong or detonated as standard procedure once the mission ended, as well as military tests.
UNKNOWN – 14.29% Assigned whenever there is insufficient evidence to support a more specific classification.
ANOMALOUS – 5.64% Unplanned separation of one or more detectable objects from a satellite that remains essentially intact, e.q. objects shedding due to material degradation such as insulation material or solar panels.
COLLISION – 9.01% There have been several collisions observed between known obiects. In some cases, the impactor is too small to be observed, but changes in the orientation and functioning of the satellite indicate an impact has occurred.
ELECTRICAL – 6.4% Events related to failures in electrical subsystems, most due to overcharged batteries exploding.
ACCIDENTAL – 0.8% Design flaws ultimately leading to breakups.
AERODYNAMICS – 0.56% A breakup most often caused when atmospheric drag leads to “overpressure.”
The good news is that as a consequence of experience, technological progress, and internationally applied space debris mitigation measures, there will likely be far fewer fragmentation events (with the possible exception of on-orbit collisions). Most internationally accepted space debris mitigation measures can be traced back to the following objectives:
- The limitation of space debris released during normal operations;
- The minimisation of the potential for on-orbit break-ups;
- Post mission disposal; and
- Prevention of on-orbit collisions.
Aspirationally, these objectives lead to a future in which space debris is not an issue.
The bad news is that with space traffic increasing, the number of in-space collisions are expected to rise – recent satellite conjunction data illustrates the problem. A satellite conjunction is an event in which two satellites or a satellite and a piece of space debris are estimated to pass near each other. The following chart shows conjunction events and corresponding space debris or satellite classification which is causing the conjunction (data is based upon a set of representative missions over 2021). The chart shows the conjunction events by orbital altitude. Note that these conjunction events could trigger an operator response but not necessarily an avoidance manoeuvre nor a collision. In the lower altitude orbits, the majority of the conjunctions are caused by constellation satellites or small satellites rather than orbital debris.
For more information regarding the history of fragmentation events, please see the following documents:
The Danger of Orbital Debris
The rising population of orbital debris increases the potential danger to all spacecraft, including to the International Space Station (ISS) and other spacecraft with humans aboard, such as SpaceX's Crew Dragon. The ISS has conducted 29 orbital debris avoidance maneuvers since 1999, including three in 2020.
More information on the effects orbital debris on spacecraft are available in the following documents:
Space activities have changed considerably since the launch of the earth's first artificial satellite, Sputnik, in 1957. Today our societies increasingly rely on a well-functioning space-based infrastructure for many critical applications including: national security and defence; communications; positioning, navigation and timing; earth observation; and weather forecasting. Orbital debris threatens the operation of all space-based applications.
The report “OECD Future Global Shocks” examined the impact of severely degraded, or complete loss, of satellite-based communications on global infrastructure. The report identified that the following infrastructure would experience widespread degradation: transportation; energy (oil and gas); information technology; finance and banking; food and agriculture. Communications infrastructure would experience widespread outages.
“The Global Risks Report 2022” published by the World Economic Forum identifies crowding and competition in space as being a key risk that the World faces. In particular, the report calls out space debris – “One consequence of accelerated space activity is a higher risk of collisions that could lead to a proliferation of space debris and impact the orbits that host infrastructure for key systems on Earth, damage valuable space equipment or spark international tensions.”
In the near term, current trends could leave some orbits inhospitable due to congestion related to spacecraft and orbital debris. Long term, increasing space traffic congestion could lead to the “Kessler Syndrome”, the situation in which the density of objects in orbit is high enough that collisions between objects and debris create a cascade effect, each crash generating debris that then increases the likelihood of further collisions. At this point some orbits will become unusable.
International Community and Orbital Debris
There are no international treaties related to orbital debris, but leading space agencies of the world have formed the Inter-Agency Space Debris Coordination Committee (IADC) to address orbital debris issues and to encourage operations in Earth orbit which limit the growth of orbital debris. In addition, since 1994 orbital debris has been a topic of assessment and discussion in the Scientific and Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). Both IADC and COPUOS have published orbital debris mitigation guidelines for the international community to follow. Furthermore, a detailed compendium of orbital debris mitigation standards used by United Nations (UN) member nations and international organizations. was produced by the UN Office Of Outer Space Affairs and has been made publicly available.
United States and Orbital Debris
Since 1988 the official policy of the U.S. has been to minimize the creation of new orbital debris, i.e., orbital debris mitigation. The 2010 National Space Policy addresses the importance of preserving the space environment, including orbital debris mitigation. NASA and the Department of Defense are also directed to pursue research and development of technologies and techniques to mitigate and remove on-orbit debris, reduce hazards, and increase the understanding of the current and future debris environment.
“Orbital debris poses a risk to continued reliable use of space-based services and operations and to the safety of persons and property in space and on Earth. The United States shall seek to minimize the creation of orbital debris by government and non-government operations in space in order to preserve the space environment for future generations (2010 National Space Policy).”
The threat from orbital debris is also highlighted in the June 2018 Space Policy Directive-3 (SPD-3), the National Space Traffic Management Policy, “Orbital debris presents a growing threat to space operations. Debris mitigation quidelines, standards, and policies should be revised periodically, enforced domestically, and adopted internationally to mitigate the operational effects of orbital debris.” The SPD-3 further states that “The United States should develop a new protocol of standard practices to set broader expectations of safe space operations in the 21st century. This protocol should begin with updated ODMSP, but also incorporate sections to address operating practices for large constellations, rendezvous and proximity operations, small satellites, and other classes of space operations. These overarching practices will provide an avenue to promote efficient and effective space safety practices with U.S. industry and internationally.” The United States Government Orbital Debris Mitigation Standard Practices (ODMSP) was updated in 2019, per SPD-3.
NASA and the Department of Defense have issued requirements governing the design and operation of spacecraft and upper stages to mitigate the growth of the orbital debris population. The Federal Aviation Administration, the National Oceanic and Atmospheric Administration, and the Federal Communications Commission also consider orbital debris issues in the licensing process for spacecraft and upper stages under their auspices.
NASA has the following internal processes and requirements currently in place:
NASA established the Orbital Debris Program officially in 1979 as part of the Space Sciences Branch. The program looks for ways to create less orbital debris, and designs equipment to track and remove the debris already in space.
Note that the NASA Orbital Debris Program publishes a quarterly newsletter “Orbital Debris Quarterly News” (ODQN). The ODQN covers the latest events in orbital debris research, offers orbital debris news and statistics, and presents project reviews and meeting reports, as well as upcoming events.
A comprehensive overview of all United States legislation and federal government organizations standards related to orbital debris is provided in the following document:
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