Iridium 9 manoeuvre - on the way down?

From: Alan Pickup (alan@wingar.demon.co.uk)
Date: Tue Sep 19 2000 - 11:10:00 PDT

  • Next message: Alan Pickup: "Decay watch: 2000 Sep 19"

    It is possible that Iridium plc has made the first tentative move in its
    plan to de-orbit its Iridium satellites.
    
    Iridium 9 (#24828 = 97- 30 C) was, until September 13, in an
    "operational" near-circular orbit between altitudes of 779 and 776 km,
    with an orbital period of 100.40 minutes. Orbital element sets issued
    since then show it some 29 km lower - the latest elset has it in a
    750x747 km orbit with a period of 99.79 minutes. 
    
    The last pre-manoeuvre elset is...
    Iridium 9        4.0  1.8  0.0  6.0 d   13       779 x 776 km
    1 24838U 97030C   00257.91101238 -.00000166  00000-0 -66348-4 0  4242
    2 24838  86.3974  27.7289 0001875  80.7395 279.3927 14.34215052169723
    ...the next one is...
    Iridium 9        4.0  1.8  0.0  6.0 d   13       750 x 746 km
    1 24838U 97030C   00258.60576252  .00250387  00000-0  71655-1 0  4065
    2 24838  86.4479  27.4432 0002500 123.2016 236.9519 14.43260369169828
    and the latest elset is...
    Iridium 9        4.0  1.8  0.0  6.0 d   13       750 x 747 km
    1 24838U 97030C   00262.97412783  .00001950  00000-0  57606-3 0  4677
    2 24838  86.4572  25.6175 0002779 108.8197 251.3316 14.43074137170456
    
    Small variations in the elsets since September 14 might be caused by
    further minor manoeuvres, though my suspicion is that they are due to
    inaccuracies in SpaceCom's determination of the new orbit.
    
    While this might be the first indication that the Iridiums are really on
    the way down, other possibilities, including a satellite malfunction,
    cannot be ruled out.
    
    Alan
    -- 
    Alan Pickup / COSPAR 2707:  55d53m48.7s N   3d11m51.2s W      156m asl
    Edinburgh  / SatEvo & elsets:    http://www.wingar.demon.co.uk/satevo/
    Scotland  / Decay Watch: http://www.wingar.demon.co.uk/satevo/dkwatch/
    
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