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Orbital Debris

Orbital debris, also known as space junk, refers to objects in orbit around Earth that do not (anymore) serve a useful function. Although orbital space is vast, high speeds create a growing risk of an orbital collision. It is necessary to take actions to mitigate the problem.

Extent

Although vast, Earth's orbital face contains many pieces of dangerous debris, especially small pieces that are difficult to track.

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Source: Liou 1.

Orbital debris have many sources, especially anti-satellite (ASAT) tests and accidental explosions 2. Following are select major events that have created debris.

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Piece of debris at least 10 centimeters in size created by several events. The 2021 Russian ASAT test was particularly destructive because the explosion occurred at a higher altitude than the other events, causing debris pieces to remain in orbit longer 3. Sources: 4,3,5,6.

Debris is less of a worry at altitudes below 600 kilometers, as a very thin atmosphere will cause objects to fall within years or less. Above 600 km, and especially above 1000 km, debris is more worrisome because atmospheric drag will not cause objects to fall in reasonable time 7.

The presence of small debris requires that satellites install shields, which adds 5-10% to the cost of satellite missions 8.

Problem:
Damage from Orbital Debris
Solution:
End ASAT Tests

Atmospheric drag and other factors will cause satellite orbits to decay, with faster decay rates at lower orbits. SpaceX Starlink satellites have an altitude of about 550 kilometers and, if ignored, fall into the atmosphere in about five years 9.

Kessler Syndrome

If a satellite is struck by a piece of debris, the explosion creates new debris, which in turn increases the risk of collision. Kessler Syndrom is a scenario in which this process becomes an uncontrollable cascade 10. The prediction market Metaculus indicates (as of August 18, 2021) a 15% chance of Kessler Syndrome by 2050, formally defined as the loss of at least 10% of satellites due to collisions with debris in one year 11. Another estimate is that in 200 years, there could be a catastrophic collision every 5-9 years, like the 2009 satellite collision 12.

In the worst case, Kessler Syndrome may put so much debris into certain orbital lanes that they become unusable. This would deny humanity the benefits of GPS, climate monitoring, satellite communications, and other services.

Mitigation

Satellite operators are supposed to move satellites at the end of their useful lives, whether that is atmospheric reentry for low-Earth orbit (LEO) satellites or a graveyard orbit for geosynchronous orbit (GEO) satellites. A graveyard orbit is at least 200 kilometers above GEO.

Satellite LocationIntended End-of-Life DestinationCompliance Rate
LEOAtmospheric Reentry20%
GEOGraveyard Orbit80%

Source: OECD 8. Satellite disposal compliance rates have been going up over time. Stronger regulation may be needed to boost compliance rates 13.

Moving a satellite from GEO to a graveyard orbit requires a Δv (change of velocity) of 11 meters per second, which subtracts on average three months from the useful life of a satellite 14. Graveyard orbits themselves have limited capacity before the collision risk is too great and threatens other orbits, making them only a temporary solution 15.

There are two major tools to protect satellites and the International Space Station against debris.

Satellite LocationIntended End-of-Life DestinationCompliance Rate
Avoidance maneuver 165+ cm
Whipple Shields 173- mm

Current debris protection efforts leave a gap between 3 millimeters and 5 centimeters for which there is not an effective defense. Research is ongoing into telescopes that will be able to track smaller pieces of debris 18.

Problem:
Damage from Orbital Debris
Solution:
Orbital Use Fee - World
Problem:
Damage from Orbital Debris
Solution:
Deorbiting Performance Bonds

Active Debris Removal

Even if launches cease today, there will continue to be orbital collisions and growth in the total amount of debris 19, so efforts to remove debris from orbit (active debris removal, or ADR) are necessary. The removal of 5-10 well-chosen objects per year should be enough to stabilize the debris environment 20. Removing 15 objects per year would cost about an estimated $600 million per year 21.

At present, no ADR occurs, though there are many possible methods 22. A demonstration mission, ClearSpace-1, is scheduled for 2025 23.

Problem:
Damage from Orbital Debris
Solution:
Research Active Debris Removal

References

  1. Liou, J.-C. "Risks from Orbital Debris and Space Situational Awareness". 2nd IAA Conference on Space Situational Awareness, Washington DC. January 2020. ↩

  2. National Research Council; Division on Engineering and Physical Sciences; Commission on Engineering and Technical Systems; Committee on Space Debris. Orbital Debris. The National Academices of Science, Engineering, and Medicine. 1995. ↩

  3. Raju, N. "Russia’s anti-satellite test should lead to a multilateral ban". Stockholm International Peace Research Institute. December 2021. ↩ ↩2

  4. European Space Agency. "About space debris". Accessed August 17, 2021. ↩

  5. Tellis, A. J. "India’s ASAT Test: An Incomplete Success". Carnegie Endowment for International Peace. April 2019. ↩

  6. Weeden, B. "2009 Iridium-Cosmos Collision Fact Sheet". Secure World Foundation. November 2010. ↩

  7. Brito, T. P., Celestino, C. C., Moraes, R. V. "Study of the decay time of a CubeSat type satellite considering perturbations due to the Earth’s oblateness and atmospheric drag". Journal of Physics: Conference Series 641: 012026. 2015. ↩

  8. Undseth, M., Jolly, C., Olivari, M. "Space sustainability: The economics of space debris in perspective". OECD Science, Technology and Industry Policy Papers, No. 87, OECD Publishing, Paris. April 2020. ↩ ↩2

  9. Kurkowski, S. "SpaceX calls on FCC to lower standard for satellite orbit life". Space Explored. February 2022. ↩

  10. Kessler, D. J., Cour-Palais, B. G. "Collision frequency of artificial satellites: The creation of a debris belt". Journal of Geophysical Research: Space Physics 83(A6), pp. 2637-2646. June 1978. ↩

  11. Metaculus. "Kessler syndrome by 2050?". February 2018. ↩

  12. Liou, J. -C., Anilkumar, A. K., Bastida Virgili, B., Hanada, T., Krag, H., Lewis, H., Raj, M. X. J., Rao, M. M., Rossi, A., Sharma, R. K. "Stability of the Future LEO Environment - An IADC Comparison Study". In Proceedings of the 6th European Conference on Space Debris 723. April 2013. ↩

  13. Office of the Inspector General, Office of Audits. "NASA's Efforts to Mitigate the Risks Posed by Orbital Debris". January 2021. ↩

  14. de Gouyon Matignon, L. "Parking Orbit and Graveyard Orbit". Space Legal Issues. May 2019. ↩

  15. European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). "Where old satellites go to die". phys.org. April 2017. ↩

  16. NASA. "Space Debris and Human Spacecraft". May 2021. ↩

  17. Aerospace Corporation. "Space Debris 101". Accessed August 18, 2021. ↩

  18. Shell, J. "Optimizing orbital debris monitoring with optical telescopes". Air Force Space Innovation and Development Center, Schriever AFD, CO. September 2010. ↩

  19. Liou, J.-C., Johnson, N. L. "Risks in Space from Orbiting Debris". Science 311(5759), pp. 340-341. January 2006. ↩

  20. European Space Agency. "Active debris removal". Accessed August 18, 2021. ↩

  21. Braun, V., Schulz, E., Wiedemann, C. "Cost Estimation for the Active Debris Removal of Multiple Priority Targets". Conference: 40th COSPAR Scientific Assembly, Moscow. August 2014. ↩

  22. Mark, C. P., Kamath, S. "Review of Active Space Debris Removal Methods". Space Policy 47, pp. 194-206. February 2019. ↩

  23. European Space Agency. "ESA commissions world’s first space debris removal". September 2019. ↩