to one of a set of defined disposal regions or maneuver to an orbit where atmospheric drag would remove the object within 25 years.

The rationale for 25 years rather than any other time period was that it was an acceptable compromise between the amount of fuel required to maneuver to a lower orbit, and the effectiveness of such a maneuver to the long-term environment, as a result of predictions by various orbital debris models. Models such as NASA’s LEGEND and the earlier EVOLVE have consistently predicted that there is only a small difference in the long-term environment between an object being removed immediately and 25 years later. Before ESA accepted the 25-year rule, ESA considered everything from zero years to 100 years for a post-mission lifetime, using the ESA MASTER’99 model. ESA concluded that “a 25-year post-mission lifetime is the shortest possible before propellant requirements start to become disproportionately high.”2

Finding: NASA’s current orbital debris programs are recognized both nationally and internationally as leaders in providing support for defining the environment and related impact hazards associated with orbital debris, and mitigation techniques to effectively minimize the hazards associated with the current and future orbital debris environment.

Finding: Most relevant federal agencies accept all or some of the components of NASA’s orbital debris mitigation and prevention guidelines.

There are two problems with the current post-mission disposal standards: (1) As described in Chapter 11, “Issues External to NASA,” not all of the spacecraft community are required to follow NASA’s standards, with at least one U.S. agency not even encouraging compliance with the 25-year rule.3 (2) Current model predictions conclude that even 90 percent compliance is insufficient to prevent future debris growth in LEO. These same models predicted the collision rates that are observed from the past four collisions between cataloged objects, as well as the amount of debris generated as a consequences of China’s anti-satellite test (Box 1.2 in Chapter 1) and the accidental Iridium–Cosmos collision (Box 9.1 in Chapter 9), providing additional evidence that the models are correct, and that mitigation alone is not sufficient. The possibility that current mitigation standards may not be adequate requires either more aggressive mitigation or the introduction of removal operations; however, the agency is not prepared for either.

The only study to determine what actions would result in a stable orbital debris environment concluded that the retrieval of pre-selected objects could do so, and would be significantly helped by compliance with the 25-year rule.4 A study by both NASA and ESA has identified some alternative techniques to remove objects.5 However, the largest activity was the “International Conference on Orbital Debris Removal” in Chantilly, Virginia, on December 8-10, 2009, sponsored by NASA and the Defense Advanced Research Projects Agency (DARPA). The conference identified many possibilities, but all required further technology development, most raised legal issues, and some introduced policy conflicts. A few might be more accurately described as enhanced or active mitigation. A report to DARPA after the conference included the observation that “any future debris removal strategy must be tested to ensure that it will work in the operating environment.”6 None of the removal or “enhanced mitigation” concepts have been fully tested or tried in the operating environment.


2 R. Walker, C. Martin, H. Stokes, J. Wilkinson, H. Sdunnus, S. Hauptmann, P.Beltrami, and H. Klinkrad, Executive summary, in Update of the ESA Space Debris Mitigation Handbook, Ref. QINETIQ/KI/SPACE/CR021539, European Space Agency, Paris, France, July 2002, available at

3 National Research Council, Summary of the Workshop to Identify Gaps and Possible Directions for NASA’s Micrometeoroid and Orbital Debris Programs, The National Academies Press, Washington, D.C., 2011.

4 J.-C. Liou, N.L. Johnson, and N.M. Hill, Controlling the growth of future LEO debris populations with active debris removal, Acta Astronautica 66(5-6):648-653, 2010.

5 H. Klinkrad and N.L. Johnson, “Sustainable Use of Space through Orbital Debris Control,” Paper AAS 10-016 presented at the 33rd Annual AAS Guidance and Control Conference, Breckenridge, Colo., February 6-10, 2010; also in Advances in the Astronautical Sciences 137:63-74, 2010.

6 D. Baiocchi and W. Welser IV, Confronting Space Debris, Strategies and Warnings from Comparable Examples including Deepwater Horizon, prepared for DARPA by RAND Corporation, Defense Advanced Research Projects Agency, Arlington, Va., 2010.

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