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From: Björn Gimle via Seesat-l <seesat-l_at_satobs.org>

Date: Tue, 26 May 2015 12:27:56 +0200

Date: Tue, 26 May 2015 12:27:56 +0200

2015-05-26 12:21 GMT+02:00 Björn Gimle <bjorn.gimle_at_gmail.com>: > Unless the satellite is controlled, all reflecting surfaces are usually > fixed. > There are essentially three modes of rotation: > E: Fixed relative to nadir and orbit plane, or velocity vector > T: Tumbling after recent explosion, meteor hit or leakages > S: Rotation around the axis of greatest inertia. > > Type T is really difficult - I can't imagine solving it. > > E is very well handled by Simone Corbellini from FPAS report submitted to > http://www.satflare.com/fpas_reader.asp > > I have solved many S cases with simple Excel calculations. When you know > the RA/Dec of the Sun and a satellite flash, > compute the unit vectors x,y,z (length 1). For the flashes, change all > values to opposite sign, then take the average of all x,y,z pairs. This > gives the normal (right angle) vector to the front side of the reflector - > convert it to RA/Dec. You need to collect flash observations in several > directions, and/or from different parts of the world. Plot the normal > vectors' RA/Dec on a star chart (with as small distortion as possible, e.g. > a stereographic projection centered near the average of thevectors), or use > the "Solver" in Excel to find the rotation axis as the point where the > distances (d) to the normal vectors are as equal as possible (minimum > standard deviation). With a current Sun position, the rotation axis, and > the (average) distance (d) from it you can compute new flash positions. > > Some complications: > Large solar panels often has a flat back side which can be sunlit and > reflecting when satellite is uncontrolled. > In the S cases this occurs as a circle at angle 180-d. > In S cases, the rotation axes precesses over months, usually at near > constant declination. You may estimate it by dividing long periods of > observations into two close groups, and/or include the precession value in > the Solver computations. > In all situations, there may be more than one reflecting surface ! > S objects affected by drag and magnetic field precess faster, and not > necessarily along declination. > Rotating cylindrical objects flash anywhere along the cylinder, when its > long axis crosses the plane perpendicular to the Sun-Satellite-Observer > plane. > > > > -------------------------------------------------------- > Björn Gimle, COSPAR 5919 > 59.2617 N, 18.6169 E, 51 m > Satellite observation formats described: > http://www.satobs.org/position/IODformat.html > --------------------------------------------------------- > > 2015-05-24 23:34 GMT+02:00 Vladislav Gooba via Seesat-l < > seesat-l_at_satobs.org>: > >> May 24 at 00:47 UT+3 I have observed very quick flares from NOSS 3-4 (A) >> #31701 and (C) #31708. The flares was -3 mag with duration shorter than >> second. Flare of (C) happened at 00:47:00+-1s. Mirror angles of (C) for >> Heavensat are 60 51.5, elongation from Sun at the moment of flare was 96.5. >> May 24 at 22:54:10 UT+3 +-10s I have observed single flare with two >> maximums from USA 215 or FIA-Radar 1 #37162. Flare duration was about 2 >> seconds, with magnitude of first maximum -1, second 0. Mirror angles for >> Heavensat are 45 243, elongation from Sun at the moment of flare was 125. >> One more question. How we can calculate flares from rotating surfaces >> such as solar panels, with unknown pattern of rotation? E.g. for fixed >> mirrors all the conditions is off-nadir and yaw angles, what is needed to >> predict flares from rotating mirrors? >> _______________________________________________ >> Seesat-l mailing list >> http://mailman.satobs.org/mailman/listinfo/seesat-l >> > > _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Tue May 26 2015 - 05:28:43 UTC

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