# Re: Bright flare from NOSS 3-4 and double flare from FIA-Radar 1

From: Björn Gimle via Seesat-l <seesat-l_at_satobs.org>
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
>
> 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?
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>
>
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Received on Tue May 26 2015 - 05:28:43 UTC

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