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FIGURE 2.3 Orbital debris program sensor capabilities for low Earth orbit orbital debris measurements. The capabilities for characterization of small debris are a function of returned samples and a variety of remote measurement capabilities. The importance of these size ranges is highlighted by their associated potential effects on space shuttle subsystem reliability. SOURCE: Adapted, courtesy of NASA, from Lyver, J., “NASA Micrometeoroid and Orbital Debris Program Overview to National Research Council,” presentation to the Committee for the Assessment of NASA’s Orbital Debris Programs, December 13, 2010, National Research Council, Washington, D.C., p. 10.

remote observations, in the case of meteoroids by measuring the meteor ion trail in Earth’s atmosphere. Smaller-size meteoroids have been measured using a multitude of in situ sensors on satellites. Similar to the situation with measurements of orbital debris, there has been more uncertainty in the remote sensing data for meteoroids than in the in situ data. The in situ data from satellites such as the three Pegasus satellites launched in 1965 has turned out to be critical in helping to resolve uncertainties in the remotely sensed data and was a major component in defining the parameters in meteoroid environment models used today. Given uncertainty in the current RCS calibrations, in situ data are also likely to be a major component in defining parameters in models of the orbital debris environment.

Although no major changes from 1960s in situ measurements of the background meteoroid flux have been detected, that is not the expectation for the orbital debris environment, which is predicted to be, and has been measured to be, much more dynamic than the meteoroid environment. Ironically, dynamic changes in the orbital debris environment were measured as a result of an experiment on the Long Duration Exposure Facility, which was intended to detect meteoroid streams. Instead of meteoroid steams, most of the 15,000 impacts detected were interpreted as being the result of Earth-orbiting debris streams.9 The source of those debris streams is still uncertain, although some streams have been associated with solid rocket motors. In addition to helping to confirm RCS calibrations, the much higher flux measured with in situ instrumentation will translate to more quickly monitoring

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9 J.P. Oliver, S.F. Singer, J.L. Weinberg, C.G. Simon, W.J. Cooke, P.C. Kassel, W.H. Kinard, J.D. Mulholland, and J.J. Wortman, LDEF Interplanetary Dust Experiment (IDE) results, pp. 353-360 in LDEF—69 Months in Space, Proceedings of the Third Post-Retrieval Symposium, November 8-12, NASA Langley Research Center, Hampton, Va., 1993; W.J. Cooke, J.P. Oliver, and C.G. Simon, The orbital characteristics of debris particle rings as derived from the IDE observations of multiple orbit intersections with LDEF, pp. 361-371 in LDEF—69 Months in Space, Proceedings of the Third Post-Retrieval Symposium, November 8-12, NASA Langley Research Center, Hampton, Va., 1993.



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