LDEF meteoroid and debris special investigation group investigations and activities at the Johnson Space Center

Since the return of the Long Duration Exposure Facility (LDEF) in January, 1990, members of the Meteoroid and Debris Special Investigation Group (M&D SIG) at the Johnson Space Center (JSC) in Houston, Texas have been examining LDEF hardware in an effort to expand the knowledge base regarding the low-Earth orbit (LEO) particulate environment. In addition to the various investigative activities, JSC is also the location of the general Meteoroid & Debris database. This publicly accessible database contains information obtained from the various M&D SIG investigations, as well as limited data obtained by individual LDEF Principal Investigators. LDEF exposed approximately 130 m(exp 2) of surface area to the LEO particulate environment, approximately 15.4 m(exp 2) of which was occupied by structural frame components (i.e., longerons and intercoastals) of the spacecraft. The data reported here was obtained as a result of detailed scans of LDEF intercoastals, 68 of which reside at JSC. The limited amount of data presently available on the A0178 thermal control blankets was reported last year and will not be reiterated here. The data presented here are limited to measurements of crater diameters and their frequency of occurrence (i.e., flux)

Interim Report of the Meteoroid and Debris Special Investigation Group

The LDEF Meteoroid and Debris Special Investigation Group (hereafter M&D SIG) was formed to maximize the data harvest from LDEF by permitting the characterization of the meteoroid and space debris impact record of the entire satellite. Thus, our work is complementary to that of the various M&D PIs, all of whom are members of the SIG. This presentation will summarize recent results and discussions concerning five critical SIG goals: (1) Classification of impactors based upon composition of residues; (2) Small impact (microimpact) features; (3) Impact cratering and penetration data to derive projectile sizes and masses; (4) Particulate flux estimates in low-Earth orbit; (5) The LDEF Meteoroid and Debris database

SUMMARY

formed to maximize the data harvest from LDEF by permitting the characterization of the meteoroid and space debris impact record of the entire satellite. Thus, our work is complementary to that of the various M&D PIs, all of whom are members of the SIG. This presentation will summarize recent results and discussions concerning five critical SIG goals: (1) classification of impactors based upon composition of residues, (2) small impact (microimpact) features, (3) impact cratering and penetration data to derive projectile sizes and masses, (4) particulate flux estimates in low-Earth orbit, and (5) the LDEF Meteoroid and Debris database

Interim Report Of The Meteoroid And Debris Special Investigation Group

This report is a first attempt to address these critical issues in a forum accessible to other LDEF investigators and the community at large, both for information purposes and also to invite critique from the larger community. Consensus on these issues has not always been achieved, as will become obvious. However, we are able to delineate the scope of disagreements and suggest ways of resolving them. For example, we recognize that much future work will necessarily concern calibration of craters in aluminum (the most common material on the LDEF), and cratering and penetration processes in the Teflon thermal blankets. As the reader has now discovered, this paper is not a global overview of M&D SIG activities, but is narrowly focussed. We discuss each critical issue below, in the order in which presented above. CRITERIA FOR DISTINGUISHING NATURAL FROM MAN-MADE IMPACTORS Introduction Since different capture experiments on LDEF employed different collection schemes and different analysis techniques, it has proved difficult to establish universal criteria for distinguishing between natural and man-made impactors. The situation becomes more complex for the entire LDEF with its myriad of experimental surfaces and analytical investigations. However, in the interest of promoting the comparisons of results from many laboratories, we propose the following classification scheme. This scheme has been employed for some LDEF studies already (ref. 1). Contamination Clearly, the level and composition of contamination must be carefully established before analysis of residues should be attempted. Also, supposedly well-understood LDEF materials often contain impurities which, though minute on a gross scale, are important at the scale necessary for analysis of impactor residues. LDEF surface..