The PSEP (Passive Seismic Experiment Package) was powered by a pair of solar panels mounted on extended arms. The one on the left (when looking towards the LEM) appears to have a matt grey backing:

crop from https://www.hq.nasa.gov/alsj/a11/AS11-40-5948HR.jpg

whereas the one on the right is much more reflective, showing both the lunar surface and the mounting struts and equipment package:

crop from https://www.hq.nasa.gov/alsj/a11/AS11-40-5951HR.jpg

I have't found any reference to this difference and my only (wild) speculation is that it was for thermal/optical properties (the left-side one only gets the face illuminated in the lunar afternoon so is presumably hotter when functioning)

  • 2
    $\begingroup$ To me this seems to be just an effect of the illumination. The first one is directly lit by the sun. The second one is in the shadow, so all you can see are the reflections. $\endgroup$
    – asdfex
    Apr 6 '19 at 11:21

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