Phobos-Grunt: doubts about manoeuvring or venting

From: Ted Molczan (
Date: Mon Nov 14 2011 - 17:22:59 UTC

  • Next message: Steve Daniels: "RE: Space Tracking and Surveillance System Demonstration Completes Mission"

    I am beginning to doubt that the very low net rate of decay that occurred between epoch date 11314.77184893 and
    11316.83198086, was due to propulsion, whether due to thruster firings or something venting. It may be that the decay
    terms of the individual TLEs of this object do not accurately reflect the true rate of decay, i.e. the spurious TLE
    hypothesis that I had rejected!
    When I consider all of the reliable TLE data (which now spans ~5 days), there seems to be a pattern such that the decay
    terms start out at what appears to be a reasonable value, but which then trends lower in subsequent elements -
    apparently because it does not reflect the actual rate of decay. Eventually, the algorithm that generates the elements
    tries to deal with the mismatch, but in a manner that results in decay terms that are now too low, even negative. That
    results in another mismatch, which continues until the algorithm makes another correction, this time reverting to a
    positive value on the high side. And the cycle repeats - unless/until adjustments are made to the analysis, perhaps by
    adjusting the duration of the data included in the analysis.
    This is a not unfamiliar TLE phenomenon, but perhaps a more extreme example than I can recall. I plan to look into this
    in greater detail, and hope to share my findings later today or tomorrow.
    Ted Molczan
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Mon Nov 14 2011 - 17:24:25 UTC