A Satobs Thought Experiment

From: Jeff Umbarger (jumbarger2000@yahoo.com)
Date: Thu Jan 08 2004 - 10:58:30 EST

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    Hey Everyone,
         Sorry about the long email to follow but in
    thinking about geosat flares, which tend to occur at
    sunset and sunrise in the opposite direction of the
    sun, I came to the conclusion that all Operational
    Satellites (OS) must flare. By OS I mean ones with
    solar panels aimed at the sun, more or less, and not
    debris such as boosters, nose cones and dead
    satellites. In order to see any OS flare you must be
    between the sun and the satellite, looking at the
    satellite. In fact, theoretically speaking, the
    optimum location is when your head casts a shadow on
    the OS. However, this could only occur *exactly* at
    sunset (or sunrise, but I'll focus only on sunset from
    here on out.) But this, of course is bright twilight
    and would be hard to see on the eastern horizon.
    However, and this is where I need help, you might not
    need to be directly in line with the sun/OS to see
    flaring. The first question:
    - If I measure the angle from me to the satellite to
    the sun (ideally, this should be zero for a flare),
    how large can this angle get before I no longer see a
    Next question:
    - How stable are most OS, in general, that is, do they
    point their panels directly at the sun or is there
    some kind of acceptable error such as up to 10
    When the sun sets in the west, I can draw line from
    the sun to my zenith to the anti-solar point (I'm not
    exactly sure what this term is but I mean the point on
    the ecliptic 180 degrees around from the sun.) I'll
    call this the SZA line and this line should clock,
    anti-clockwise looking up,  around my zenith as the
    sun sets, the anti-solar point (AS point) rises in the
    east and goes to my south (for the northern
    hemisphere). In fact this line should run straight
    north and south at my local midnight when the AS point
    is highest. I mention this line because it represents
    a measuring stick for eclipsing OS at various
    altitudes. Right at sunset, if it went completely
    dark, I should see every OS flare that passes through
    the SZA line near or above the AS point. As the
    twilight progresses and the AS rises and the SZA line
    rotates above me, the eclipse point for each altitude
    - from 0 km to 40,000 km - should begin to spread out
    up this SZA line from the AS point, with lower orbits
    racing ahead up the line and the higher orbits moving
    behind these - all of them spreading out like an
    accordion until my local midnight and then
    recompressing back to the AS at sunrise. (It would be
    interesting to map the path of a set of altitudes with
    time on the local midnight star field.) Anyway, what
    I'm interested is where to look down this SZA line for
    the best opportunity to see a flare. Next question:
    - Given a histogram curve of all OS by altitude (a
    plot showing # of OS's vs. average altitude) where
    would the peak of that curve be, that is, what is the
    altitude of most OS's (not counting geosats)?
    Given this altitude I could then determine the where
    to look down this line with time. At some point the
    observer-satellite-sun angle would exceed flaring
    - Has anyone ever looked for this type of flaring at
    - Is the flare angle to small so that the only
    opportunity is in bright twilight right after sunset?
    I'll be going to Hawaii, the island of Maui, the week
    of Jan 18 (new moon). I'll be going up on top of Mt.
    Haleakala (a 3050 meter volcano) and looking for this
    effect. I figure with the thin air I should be able to
    see dimmer flares, the twilight should end sooner, and
    I'll be able to look "down" to the eastern horizon.
    Before I've seen the shadow of the peak (on which I'm
    standing) rise up in the east - so this is where I'll
    be looking. Thanks for any help with the above
              Jeff Umbarger
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