Introduction/Background - The Polished Plate Meteoroid and Debris Experiment (PPMD experiment), one of the four experiments that made up the Mir Environment Exposure Package (MEEP), was exposed in a Passive Experiment Container (PEC) on the exterior of the Mir/Shuttle docking module (Figure 1) for approximately 18 months (from March 1996 until October 1997). The PEC containing the PPMD was oriented on Mir such that one exposed experiment surface faced predominately in the ram direction (+Y in the Mir coordinate system) and the other exposed experiment surface faced predominately in the wake direction (-Y in the Mir coordinate system).

The primary objective of the PPMD experiment is to investigate the meteoroid and man-made debris environments being encountered by Mir. A secondary objective of the experiment is to investigate the Mir and Shuttle induced contamination deposited on surfaces exposed externally on Mir. The PPMD experiment was exposed to contamination from Mir during the entire 18 months. It was exposed to contamination from the Shuttle during the four Shuttle visits to Mir that occurred during the 18 months the PPMD Experiment was open.

Experiment Description - The PPMD experiment is passive and thus all results are derived from comparisons of pre-flight and post-flight laboratory measurements of the experiment surfaces. The two exposed PPMD experiment surfaces were mirror images of each other with the exception of the center panels (Figure 2). The center panel that faced the +Y direction is gold and the center panel that faced the -Y direction is aluminum. All of the edge panels are zinc. Pin Hole Cameras and optical and electron microscope specimens were also mounted on each exposed surface for additional orientation and cleanliness measurements respectively. All of the experiment hardware was in ultra clean condition (Mil-Std. 1246C 200 A/10) when launched.

Quick Look Results - The most noticeable feature observed during the post-flight quick look examination of the retrieved experiment was that of residue and stains remaining from liquid splatters on the ram facing experiment surface (Figure 3). These splatters were also visible on the edge of the PEC that faced the rod that attached the PEC to Mir. The shapes and shadowing of the stains and residue indicated that the source of the liquid was somewhere in the -Z direction. The residue is water soluble and the splatters cover approximately 10% of the ram facing experiment surface. Preliminary IR and energy dispersive spectroscopy indicate nitrogen, oxygen, sodium, sulfur and phosphorous in the dry residue. The microscopic appearance, and the relative amounts of these elements vary from spot to spot. Waste dumps are one candidate source for this residue. The wake facing surface of the experiment visibly appears to be clean (Figure 4). Microscopy and chemical analyses of the deposited residues (from both the spatters and molecular deposition) and studies of the chemical analysis of typical shuttle waste dumps, which maybe a source of the spattered liquid, are continuing.

Eight impact craters, the largest being approximately 1 mm in diameter, were also observed during the quick look examination of the retrieved experiment surfaces. Microscope surveys of the surfaces to count and measure the more numerous smaller craters are currently being conducted. After the completion of the microscope surveys, individual craters will be studied in electron microscopes, SEMS and other instruments to measure the composition of the residues of the impactors that remain in the craters. The location and studies of the impactor residues in many small craters will be complicated by the large quantities of contamination present on the surfaces.