AEHF 1 - period of brightness variation

From: Ted Molczan (
Date: Sun Aug 29 2010 - 18:20:13 UTC

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    In several posts to the list, Kevin Fetter has provided video showing bright flashes from AEHF 1,
    recorded on Aug 29 UTC. My analysis of the times, suggests a period of variation of about 301 s,
    which may indicate that the spacecraft is rotating at 0.1 RPM.
    I judged the frame of peak brightness of each recorded flash as follows:
     Aug 29 UTC
    The space between the first and second time is ~20 min, but the space between subsequent times is
    ~15 min, which suggests there were fainter flashes at ~5 min intervals between the above times. In
    response to my query off list, Kevin seemed to recall noticing fainter flashes lasting a fair number
    of seconds, followed by brighter flashes of much shorter duration.
    Numbering the above flashes as 0, 4, 7, 10, and fitting a linear equation to the elapsed time since
    flash 0, yields a coefficient of determination of almost exactly unity, indicating a strong
    correlation; with slope of 301.1 s, and intercept of -0.26 s.
    Kevin, if you can find and report other flash times on your video, regardless of brightness, the
    information would be useful in testing the hypothesis of a ~301 s period. If it is confirmed, then
    the spacecraft may be rotating at 0.1 RPM or 0.2 RPM depending on symmetry. 
    Rotation of AEHF at 0.1 RPM would not be unexpected, since it is built on an A2100 bus, and as part
    of some research last summer, I found evidence (in several launch press kits) that satellites based
    on the A2100 bus rotate at 0.1 RPM at deployment.
    Ted Molczan
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