Superbird A thoughts

Rob Matson (Rob_Matson@cpqm.mail.saic.com)
2 Oct 1996 14:55:23 -0800

                      Subject:                              Time:  11:37
  OFFICE MEMO         Superbird A thoughts                  Date:  96/10/02

To Jim Varney, Robert Sheaffer, et al.:

This Superbird rotation business is getting interesting.  I finally decided I
needed to see a picture of what the earth looks like from the satellite's
point of view at the time when flashes are being observed.  Basically, the
satellite is centered over the middle of the Pacific Ocean, almost due south
of Hawaii at latitude 1.6 S, longitude 161.1 west at an altitude of roughly
36960 km.  The terminator is curved, concave to the left, such that Hawaii is
still sunlit (but just barely).  So you've got a slighly gibbous earth, lit on
the left side.

Looking at the earth nadir-point from Superbird, with "up" defined as toward
the north pole, the sun is to the left and just slighly "behind" you.  The
angle from the sun to the satellite to southern California is 113 degrees at
3:25 UTC, 112 degrees at 3:30 UTC.

Now, in order for a specular reflection to hit southern California at 3:30
UTC, the mirror must be pointed 56 to the right of the sun and 56 degrees to
the left of SoCal.  It also must be pointed in a direction nearly parallel to
the earth's equatorial plane.

I had assumed that for southern CA, northern CA and Colorado to all be seeing
flashes that the specular reflection would have to sweep roughly pole-to-pole,
with the CA locations seeing their peak flashes a little later than Colorado
due to the slow solar motion relative to the earth-satellite line. However,
from the vantage point of the satellite the reflections could just as easily
be sweeping from right to left, left to right, or anywhere in between. 
Because of the huge reflection sweep velocity, it would be virtually
impossible to tell which way the sweeps are going across the globe based on
the timing of specific flashes.
But there's no need to time specific flashes.  Finding the time of maximum
flash brightness from multiple locations should do the trick.