Re: Re: MetOp-A seemingly a bit late

From: alain.figer@club-internet.fr
Date: Thu Sep 06 2007 - 08:54:37 EDT

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    Big acknowledgements and thanks to Björn who definitely solved the little mystery about MetOp-A.

    In fact, as he pointed it out, I misidentified MetOp-A with its "red herring" Meteor Priroda rocket (1981-65 B), observed within about 1sec of the H-A prediction. My estimation of that rocket brightness was a  4.7 magnitude at 25° altitude (and 33° azimuth : NE-NNE).

     

    That is to say MetOp-A must have been rather faint, since I *especially* waited for it passing through my B10x50 field, without being able to spot it ... and being forced to wait for the following satellite to come !

    In such a binoculars field of 11 Persei (BSC 785 ; HIP 12692) I would have expected a limiting magnitude for a satellite of at least 6.2  taking in account the very luminous area of my parisian sky at low altitude (whereas I had for example that same night a more convenient limit at mag 7.5 in Polaris field)

     

    =>  I should have been more wary about spotting MetOp-A in that poor sky area, since I had already observed another very faint pass of MetOp-A, in Cassiopeiae, irregularly varying between mag 6 and mag 7, just a few days before, on August 29, 2007.

     

    Moreover, note that I also observed that night of sept 4, about half an hour later than its rocket,  Meteor PRIRODA (1981-65 A) , in Cassiopeiae, spotting it within 1sec of the H-A predition, that figure being my current error bar (when not trying harder : 0.2 -0.3 sec being in that case near of my best).

     

    Finally here is a remark about the "red herring" concept.  :-)

    40 years ago, when I was observing satellites with my friend Jean Lecacheux of Meudon Observatory, we used to use, instead of the "red herring" label, the following meaning in french : "un chalutier"... in reference to the quite many "soviet trawlers" that used to be spying the US technology at the cold war time - seemingly without especially seeking to hide well themselves !!

     

    Regards

    Alain

    Western suburbs of Paris (France)

    48°.891 N

    2°.113 E

    altitude 45 m


    ----Message d'origine----
    De: Björn Gimle (GlocalNet)
    A: alain.figer@club-internet.fr
    Sujet: Re: MetOp-A seemingly a bit late
    Date: Thu, 6 Sep 2007 11:47:35 +0200
    boundary="----=_NextPart_000_004F_01C7F07B.B748E580"

     
    I agree, although MetOp-A alternates between normal and negative drag in a sawtooth pattern.
    This drag/slow orbit correction is so small that it takes about four weeks
    for a +drag elset to be 21 sec late wrt the previous -drag one.
    But the cycle is about 2.3 days up, 2.3 days down, so compared to reality
    the +drag elset must be >6 weeks old to show this discrepancy.
    No sudden MM jump has occurred in the last two weeks.

    So if you verified that H-A used a 04 Sep elset, with MM=14.2149...,
    I suggest your timing was off, or you saw a "red herring" (different object)

    06-44A 29499 METOP-A should have passed 3' ABOVE 11 Per 19:38:49
    81-65B 12586 SL-3 R/B 16' below 11 Per (HP061292) 19:39:09

    /Björn
    ----- Original Message -----
    From: alain.figer@club-internet.fr
    To: SeeSat-L@satobs.org
    Sent: Wednesday, September 05, 2007 9:10 PM
    Subject: MetOp-A seemingly a bit late

    From my place, 2006-044 A MetOp-A passed, on september 4th,  0°2 below the star 11 Per at 19h39m08s UT, that is 21 seconds later than expected from the Heavens-Above charts (for epoch 4sep). 

    Rather an unusally large time delay.

     

    Regards

    Alain

    48°.891 N

    2°.113 E

    altitude 45 m

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