Starshine decay

From: Alan Pickup (
Date: Fri Feb 18 2000 - 08:55:49 PST

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    Gil and Harro,
    It is just as well that you, Gil, asked for emailed elsets since the one
    for 00049.48035817 has yet to become available via OIG. OIG has also
    failed to post any decay warnings since the one issued at 09:46 UTC so
    it is good that we had the alternative route for these too.
    I don't know whether to expect any further elsets, but I guess not. I
    had posted a prediction at 08:20 UTC this morning, predicting the decay
    for 15:04. Since then, we have received three more elsets showing it,
    respectively, 0.1 sec early, 3.4 sec early and (for the 00049.48 elset)
    7.2 sec early against my prediction
    A new set of calculations suggest that Starshine may have decayed on a
    northbound pass over the Atlantic and Africa, perhaps near Lagos,
    Nigeria, at 14:28 UTC. This is more than one hour before SpaceCom and
    Harro, but I have difficulty in keeping Starshine in orbit to reach even
    the southbound equator crossing at 15:12 UTC. For what its worth, here
    is an elset for the equator crossing at which I claim, or rather
    "guess", it was close to decay...
    Starshine        1.0  0.0  0.0  9.0 d 0.30       119 x 118 km
    1 25769U 99030B   00049.60136312 2.59942209  50000+2  89468-3 0 93422
    2 25769  51.5790   5.5397 0000738 270.0144  89.9772 16.57999085 42112
    I remain suspicious of the drag (ndot) and Bstar terms in SpaceCom's
    TLEs and I wonder whether your iterations/computations, Harro, use these
    values from the elset. If I recalculate the ndot terms using the mean
    motion over a range of elsets close to decay, I usually find a higher
    value for ndot than the one in the TLE. For example...
    Elset epoch      Elset ndot    Computed ndot...using mean motion
                                                   from elsets at...
    00049.23746154   0.06695398     0.08463523     00049.11/.35
    00049.35901652   0.09446491     0.11981190     00049.23/.48
    In both cases, the computed ndot is >25% higher than the one quoted in
    the elset. In my analyses, I (almost always) derive my own values for
    ndot and mean motion by carrying an orbital evolution through the
    satellite positions described by the elsets over the past day or so.
     Alan Pickup | COSPAR 2707:  55d53m48.7s N  3d11m51.2s W   156m asl
     Edinburgh   | Tel: +44 (0)131 477 9144     Fax: +44 (0)870 0520750
     Scotland    | SatEvo page:
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