DSP aperture cover - physical characteristics

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Wed Oct 06 2010 - 22:48:44 UTC

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    Scott Campbell's recent discovery of the aperture cover of DSP F18 (97008E / 27680), led me to
    attempt to learn about the physical characteristics of these objects. So far, I have found that all
    are discs of ~1 m diameter, and the one from DSP F16 is specularly reflecting on at least one side.
    I also found photos of a few red coloured aperture covers, but am not certain that they were the
    ones that were launched. For supporting information, please read on.
    There are numerous photos and drawings of DSP satellites on the web, but few show the aperture
    cover. Drawings depict the spacecraft after the cover would have been deployed. Photos taken during
    construction or in pre-flight processing, tend to be taken from below the aperture. 
    Fortunately, one DSP was deployed from a shuttle: DSP F16 (91080B / 21805) on STS 44 (91080A /
    21795), and its aperture cover is clearly visible in a few still photos, and some video taken during
    the deployment.
    My reaction upon seeing this photo was that the aperture cover must be white:
    But the mottling in this one suggested that it was specularly reflecting the Earth's cloud cover:
    Further searching turned up the confirming data, in the form of the thumbnail photo and video here:
    The video includes the raising of the DSP into its deployment position, revealing an ever-changing
    reflection of space and Earth, as the aperture cover moves relative the camera. So, it definitely is
    mirror-like - at least on one side.
    Drawings in NASA's STS 44 media resource kit, enable estimating the diameter of the cover:
    Assuming the payload configuration drawings on pg. 17 are to scale, then the known dimensions of the
    payload bay, or the IUS (see pg. 23), can be used as the basis. My results round to 1 m.
    Fig. 55 of the following document (size: 28 MB) shows all five DSP variants, and includes a scale,
    which leads me to conclude that all have a 1 m aperture:
    Some of the DSP photos appear to show red-coloured aperture covers, but it is unclear to me whether
    those were the same covers that were launched. A clearer example appears in this article:
    Ted Molczan
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