Superbird A secondary flashes

ROB MATSON (ROBERT.D.MATSON@cpmx.saic.com)
18 Jun 1998 14:15:26 -0800

Hi All,

Congrats to Stuart Jackson for his observation of Superbird A on 18 Jun UTC.
I've done a preliminary analysis, and have determined that he observed
specular reflections from a secondary surface (something other than a
solar panel).

Superbird A was built by Loral Space Systems using the FS-1300 bus.  It
was launched on an Ariane 44L on June 5, 1989, out of Kourou, but suffered
a hydrazine propellant leak which put the satellite into a slow spin.  Based
on years of collected flash data from a network of observers, it is my belief
that the spin axis is perpendicular to the long axis through both solar arrays, such that the satellite is tumbling "end over end" or "paddle-wheel" fashion.

The solar arrays on either side of the satellite must be pointed in opposite
directions because equal brightness glints are observed on the half-period
during the middle of the flash window.  (If the arrays were pointed in the
same direction, the flashes from one side would always be brighter than
the other since the reflectivities are very different on either side of an
array).

But for Stuart to observe flashes when he did, another surface had to
have been involved.  The pointing normal of the surface causing the
flashes he observed is only tilted about 20 degrees from the axis of
rotation.  (The solar arrays are tilted 90 degrees from the rotation axis.)
Looking at a picture of the FS-1300 bus, there are two circular antennae attached to the bus, one of which may be the cause of the secondary
flashes.  These antennae are much smaller than the solar arrays, which
would explain why Stuart only observed flashes in the mag 5.5-6.0 range.
(Solar panel flashes are closer to magnitude 2.5-3.0, or about 16 times
brighter.)

Based on this observation, I will provide secondary flash window time
predictions in a subsequent message.  --Rob