of shape in the standard breakup model. These enhancements would also serve to improve BUMPER’s accuracy in predicting risks.

Recommendation: The NASA Orbital Debris Program Office should expand its efforts to more accurately incorporate data on sources of debris into the standard breakup model, especially (1) empirical results from recent major on-orbit collisions, (2) data from laboratory rocket body collision tests (which need to be planned and conducted), (3) results from hypervelocity impact tests with payloads using newer construction methods and materials, and (4) enhanced data on fragment shape characteristics.

Recommendation: NASA’s Orbital Debris Program Office should release the next version of the Orbital Debris Environment Model as soon as possible and provide updates on a regular basis or as often as required as a result of major changes to the orbital debris environment or improved characterization of that environment, including characterization of debris shape, as applicable.

CHAPTER 4: THE METEOROID ENVIRONMENT AND ITS EFFECTS ON SPACECRAFT

Finding: The models used to relate measurements of plasma to fundamental parameters of a meteoroid contain large uncertainties and errors. These models include, but are not limited to, electromagnetic scattering models, luminous emission models, and meteoroid fragmentation models.

Finding: Because the scientific community infers the properties of a meteoroid indirectly from its effects on the atmosphere (a meteor) or the effects of its impact on a spacecraft, it is imperative to understand observational biases inherent in each instrument that affect the detection of these secondary effects.

Finding: The Meteoroid Environment Model incorporates in its predictions the latest available data on the meteoroid environment, including the directionality and full velocity distribution of the meteoroids. It is currently the NASA model that is most consistent with the known meteoroid environment, although some major uncertainties still remain.

Recommendation: The NASA meteoroid and orbital debris programs should establish a baseline effort to evaluate major uncertainties in the Meteoroid Environment Model regarding the meteoroid environment in the following areas: (1) meteoroid velocity distributions as a function of mass; (2) flux of meteoroids of larger sizes (>100 microns); (3) effects of plasma during impacts, including impacts of very small but high-velocity particles; and (4) variations in meteoroid bulk density with impact velocity.

Finding: The earlier SSP 30425 meteoroid model does not reproduce existing observational meteoroid data with a fidelity equal to that of the Meteoroid Environment Model. Numerous disparate sources of data have been fused to produce the current meteoroid flux model used by NASA, sometimes incorporating differing underlying assumptions.

Finding: The Meteoroid Environment Model currently does not extend to prediction of the meteoroid environment in the outer solar system, and the measurements it incorporates are poorly constrained in the cis-martian region.

Recommendation: An effort should be made to re-examine earlier data used in the Grün Interplanetary Flux Model and to reconcile the data with more recent measurements in the literature on meteoroid flux, and a technical evaluation should be undertaken to synthesize and document such data as it is incorporated into the Meteoroid Environment Model (MEM). Updates of the MEM and technical development should follow a technical pathway as rigorous as that being taken for updates of the Orbital Debris Environment Model.



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