Re: Lacrosse 5 "disappearance trick" captured

From: Philip Masding (
Date: Sat Jul 29 2006 - 07:58:52 EDT

  • Next message: Marco Langbroek: "Re: Lacrosse 5 "disappearance trick" captured"

    Sorry to say I didn't observe this pass and as John Locker reported it was 
    cloudy for him it was probably cloudy here to (about 40 miles away).
    I have now had a look at a VRML simulation of the pass. Now I should say 
    that Marco reported 2 flares of L5 to me earlier in the year (on February 25 
    and March 4) and I saw one on March 6. All these were consistent with a flat 
    SAR panel inclined between 25 and 36 degrees to the Earth's surface and the 
    satellite flying in YVV mode.
    Now if I use YVV and 33 degrees for Marco's disappearence trick pass I see 
    that around the time the satellite disappeared the SAR panel may have gone 
    into the shadow of the solar panel. Actually VRML does not do shadows so I 
    have to manipulate the scene so I am looking in the same direction as the 
    Sun and then I see the SAR is behind the solar panel. If the SAR had not 
    gone into that shadow then conditions would have been right for a bright 
    pass - close to a flare in fact. This assumes the Solar panel is on the 
    sunward side of the SAR which would be a good idea I guess if you want to 
    get the most power out of the solar panel.
    The solar panel itself would have been seen almost edge on and so wouldn't 
    have been very bright.
    Marco have you any idea what your limiting magnitude is for the moving 
    satellite is? I suppose it is fainter than the cut off for the stars which 
    you are tracking.
    Also if the YVV/33 degree theory is correct Marco has a chance to observe 
    flares in the next few days
    Flare Results for Observer Lat=52.15412 Long=4.49081
    Satellite NORAD 28646
    Flare Results for Flight Mode YVV Panel Angle 33
    12. SAR MA 2.97104043228698 at 31/07/2006 21:51:22 Alt=74.2391395227923
    24. SAR MA 1.94970371097394 at 03/08/2006 01:11:48 Alt=81.734351847199
    26. SAR MA 4.33582695558342 at 03/08/2006 20:49:54 Alt=66.8716914873383
    Now looking at the VRML for each of these it occurs to me that the incoming 
    sunlight is very close to 90 degrees to the orbital plane and I guess this 
    will be the condition for the disappearing trick. I think the precise angle 
    is calculated by the simulator program somewhere.  More later .....
    This is a fascinating mystery!
    ----- Original Message ----- 
    From: "Marco Langbroek" <>
    To: "satellite list" <>; "Ted Molczan" 
    <>; "Bruce MacDonald" <>; 
    "Pierre Neirink" <>; "Scott Campbell" 
    <>; "Greg Roberts" <>; "Bram Dorreman" 
    Sent: Thursday, July 27, 2006 1:19 AM
    Subject: Lacrosse 5 "disappearance trick" captured
    > Lacrosse 5 is still doing its odd rapid "disappearance trick"...
    > An hour ago, I captured it in the act of doing so with my camera, while it 
    > was almost overhead for me. See image here:
    > This is a 10.7 second exposure, and movement is upwards. Lyra is well 
    > recognizable. Some 6 seconds after the start of the exposure, the sat 
    > disappears. The end of the trail at the end of the exposure should be 
    > between 13 & 16 Lyrae (the two stars "above" the trail): but it disappears 
    > much earlier.
    > Note that it wasn't near shadow entry at all.
    > The sat was perfectly on-time and on-track by the way (position will 
    > follow). At the start of the exposure it was mag +1.5
    > - Marco
    > -----
    > Dr Marco Langbroek  -  SatTrackCam Leiden, Cospar 4353
    > Leiden, the Netherlands. 52.15412 N,  4.49081 E (WGS84), +0 m ASL
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    > -----
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