Dr. Bill Cooke
Marshall Space Flight Center

University of Florida Astronomy Colloquium - Sept. 20th, 2006

The Engineering Side of Dust: Micrometeoroids and the Risk They Pose to Spacecraft

The recent loss of the orbiter Columbia and its crew, while not caused by a meteoroid strike, has resulted in re-evaluations of the current meteoroid models used by NASA and other agencies. The most prevalent of these, that published by Grun et al. in 1985, assumes an isotropic meteoroid background in which all meteors travel at speeds of 20 km s^-1, and is clearly oversimplified. The standard Divine NASA interplanetary model, currently called METEM, is a set of empirical fits to data using distributions that have little or no resemblance to reality; consequently, the model's environment directionality and velocity distributions are in error. The recommendation of the Columbia Accident Investigation Board's (CAIB) report that meteoroid risk to Space Shuttle missions be evaluated in a manner similar to that used for the International Space Station, combined with the insistence of internal NASA reviews that these environment assessments be accompanied by confidence levels or uncertainties, is a driving force behind the development of new, physics-based meteoroid environment models for near-Earth space and elsewhere.
Such models, of course, must be calibrated. In-situ measurements by spacecraft would be ideal, as they can sample throughout the Solar System. However, the small collecting area of current detectors renders them practically useless for detecting particles with sizes capable of causing spacecraft damage, which is greater than 100 microns. Fortunately, ground-based sensors, such as radar, can, at least in principle, measure the fluxes of particles in the threat regime, thereby providing the necessary calibration points; it is also possible that IRAS, COBE, and Spitzer observations of zodiacal light and asteroidal dust bands can play a significant role. This talk will give a brief overview of our current state of knowledge concerning the near-Earth meteoroid environment and the risks it poses to various vehicles, highlighting the major unknowns and areas where more research is needed.