Satellite impact probabilities: Annual showers and the 1965 and 1966 Leonid storms

The stream meteoroid impact probability for space platforms is reviewed and found to be very low under normal circumstances. While the literature cont ains numerous accounts of spacecraft apparently suffering damage and/or int erference during meteoroid stream encounters, we find that there is, in fac t, very little evidence to support such claims. This conclusion may not be valid, however, during meteor storms, when the flux of visual meteors can i ncrease by factors in excess of 10(3) to 10(4) of that from the sporadic ba ckground. Special attention is directed towards the Leonid meteor storms of 1965 and 1966-the only meteor storms since the dawn of the space age. The space platform impact probabilities during the 1966 storm were small but no ne negligible, being of order 1% for an exposed surface area of 2 m(2) at a limiting meteoroid mass of 10(-7) (and assuming a stream mass index s = 2. 0). The circumstances surrounding the possible encounters of the Pegasus II and III, and Mariner 4 spacecraft with Leonid stream meteoroids are discus sed in some detail. While the 1966 Leonid meteor storm is the strongest on record (in the sense of the highest visual meteor rates) no apparent meteor oid inflicted damage to a spacecraft can be unambiguously linked to it. Thi s result is mostly a consequence of the small number and small size of spac ecraft in Earth-orbit at the time of the 1966 storm. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.