Re: Flaring of ERS-1

From: Björn Gimle (b_gimle@algonet.se)
Date: Fri Apr 18 2003 - 03:49:53 EDT

  • Next message: Peter Wakelin: "SATOBS 2003 April 18"

    All satellites that have solar panels or other flat surfaces flare,
    unless they are controlled so that they always point (away from or)
    nearly straight to the Sun, or other unfavourable angles, such as being
    shadowed by other parts of the satellite body.
    The Iridium solar panels are, depending on the "latitude" of the Sun
    above the orbital plane, fixed, or just rotating in the orbital plane,
    and IridFlar predicts those flares quite accurately. The KeyHole
    satellites often flare when rising in the S (in summer) or exiting shadow
    further N - sometimes flash a few times later like if re-targeting.
    another satellite with long flares is SeaSat 1
    
    When a satellite suffers a malfunction, it is initially tumbling, which
    for practical purposes appears as unpredictable flashing. Gradually, this
    tumbling is transformed into a rotation around the axis of greatest
    inertia, with a well defined period, and the reflections sweep over
    "circles" on the celestial sphere, and the axis and cones can be be
    computed (and flash positions computed) given enough observations.
    
    For satellites in low orbit, atmospheric, magnetic and gravitational
    disturbances create a need for a lot of observations in various
    directions over a short time span, and for the tumbling Iridiums this is
    practically impossible because of the many flat surfaces. Also
    predictions would not be valid for long.
    
    Satellites in geosynchronous orbits often flash to between +3 and +7 for
    a short or long time span every night, and can be predicted given several
    observations over a time span of several months. Cosmos 2282 has a long
    time span, Superbird A and the DSPs very short. Operational ones ususally
    flare just as they enter or exit shadow, when their declination match
    that of the Sun. Some also flare three-four hours before and after
    because of reflectors beside the panels.
    
    When/if a rotating satellite is slowed down to a period of several
    minutes, the flashes gradually transform into flares.
    
    I hope other observers contribute hints on more flaring satellites.
    
    /Björn
    
    ----- Original Message -----
    From: "Petter B. Aslaksen" <aslaksen@stud.ntnu.no>
    To: "SeeSat-L" <SeeSat-L@satobs.org>
    Sent: Thursday, April 17, 2003 11:30 PM
    Subject: Flaring of ERS-1
    
    
    > I observed the ERS-1 tonight as it was passing pretty much through
    zenith
    > at 22.41 local time. Heavens-above.com claims that the maximum
    brightness
    > is 4.8 of this satellite. But, I am certain that for maybe a couple of
    > seconds it was maybe magnitude -1 or at least magnitude zero. Do all
    > satellites flare up like this if the angles are right? Sure enough, it
    > wasn't as spectacular as an iridium flare, but still, it makes me
    wonder
    > if it was something else I saw. Anyone know the answer?
    >
    > Petter,
    >
    > Trondheim, Norway (63.40 N, 10.433 E)
    >
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