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
flare?
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
degrees?
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
condition.
- Has anyone ever looked for this type of flaring at
sunset?
- 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
questions.
Regards,
Jeff Umbarger
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