Passivation (spacecraft)

The passivation of a spacecraft is the removal of any internal energy contained in the vehicle at the end of its mission or useful life.[1] Spent upper stages are generally passivated after their use as launch vehicles is complete, as are satellites when they can no longer be used for their design purpose.

Internally stored energy generally takes the form of unused propellant[1] and batteries.[2] In the past, such stored energy has sometimes led to fragmentation or explosion, producing unwanted space debris.[1][2] This was a fairly common ultimate outcome for many of the legacy US[3] and Soviet rocket designs of the 1960s–1980s.[4] However, the problem of derelict second stages left to orbit long-term in higher Earth orbits breaking up has not totally gone away; several US rocket stages fragmented in just the last two years of the 2010s.

The International Telecommunications Union (ITU) and United Nations (UN) recommend that satellites in geosynchronous orbit be designed to move themselves to a disposal orbit some 350 kilometres (220 mi) above the GEO belt, and then remove internally stored energy. Most GEO satellites conform to these recommendations, although there are no enforcement mechanisms.[1]

Standard practices

Within national regimes, where national governments can control the launch licenses of launch vehicles and spacecraft, there are some enforceable requirements for passivation.

The US government has implemented a set of standard practices for both civilian (NASA) and military (DoD/USAF) orbital debris mitigation that require passivation for space launches with US launch licenses. "All on-board sources of stored energy of a spacecraft or upper stage should be depleted or safed when they are no longer required for mission operations or postmission disposal. Depletion should occur as soon as such an operation does not pose an unacceptable risk to the payload. Propellant depletion burns and compressed gas releases should be designed to minimize the probability of subsequent accidental collision and to minimize the impact of a subsequent accidental explosion."[5][6]

Passivation practice on many launches in recent decades has not mitigated second stage breakups. Upper stage deflagration/breakup events have continued even with newer rocket designs of the 2010s, long after the negative externality of space debris became widely considered as a much larger social problem. For example, there were three upper stage breakups in just the late 2010s:

  • 30 August 2018: Atlas V Centaur passivated second stage launched on 17 September 2014 broke up, creating space debris.[7]
  • 23–25 March 2018: Atlas V Centaur passivated second stage launched on 8 September 2009 broke up.[8][9]
  • 6 April 2019: Atlas V Centaur passivated second stage launched on 17 October 2018 broke up.[10][11]
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References
  1. Johnson, Nicholas (2011-12-05). Livingston, David (ed.). "Broadcast 1666 (Special Edition) - Topic: Space debris issues" (podcast). The Space Show. 1:03:05–1:06:20. Retrieved 2015-01-05.
  2. Bonnal, Christophe (2007). "Design and operational practices for the passivation of spacecraft and launchers at the end of life". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. 221 (6): 925–931. doi:10.1243/09544100JAERO231. ISSN 2041-3025.
  3. 50-Year Old Rocket Stage Involved in Orbital Debris Event, Spaceflight 101.
  4. A. Rossi et al, "Effects of the RORSAT NaK Drops on the Long Term Evolution of the Space Debris Population", University of Pisa, 1997.
  5. "U.S. Government Orbital Debris Mitigation Standard Practices" (PDF). NASA. United States Federal Government. Retrieved 2013-11-28.
  6. "Orbital Debris – Important Reference Documents". NASA Orbital Debris Program Office. Archived from the original on 2016-07-02.
  7. Agapov, Vladimir (29 September 2018). "Major fragmentation of Atlas 5 Centaur upper stage 2014‐055B (SSN #40209)" (PDF). Bremen: International Academy of Astronautics Space Debris Committee. Retrieved 22 April 2019.
  8. "Rocket break up provides rare chance to test debris formation". European Space Agency. 12 April 2019. Retrieved April 22, 2019.
  9. David, Leonard (April 23, 2019). "Cluttering Up Space: U.S. Rocket Stage Explodes". Retrieved 22 April 2019.
  10. @18SPCS (24 April 2019). "#18SPCS confirmed breakup of ATLAS 5 CENTAUR R/B (2018-079B, #43652) on 6 April 2019. Tracking 14 associated pieces – no indication caused by collision" (Tweet) – via Twitter.
  11. "ATLAS 5 CENTAUR R/B". N2YO.com. Retrieved 22 April 2019.
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