Another Naked-eye Geosat Flasher

Richard Baldridge (RBaldridge@Filss.com)
Tue, 17 Aug 1999 09:02:12 -0700

This object may already be known to the SeeSat group, but just in case
it isn't . . .

I observed a "SUPERBIRD A"-like Geosat flashing to naked-eye brightness
(2nd-3rd magnitude) on August 16 at 4:34UT.  The next night, Aug 17th
UT, I reacquired the satellite and obtained further flash timings and
some positional data.  The satellite has essentially the same flash
pattern as Superbird-A, with two sets of flashes that alternate bright
and dim but with a "center" period where the flashes are nearly equal in
brightness.

The "discovery" was made naked-eye while observing regular LEO
satellites and watching for Perseid meteors.  My eye caught a near 1st
magnitude flash just east of Ophiuchus at around 4:30UT on August 16th
from my observing location at N37.272 W121.977 in Campbell, CA USA
(currently -7 hours from UT.)  I easily spotted another flash and made a
crude estimate of the flash period as 28 seconds and marked an
approximate location on a chart.  Approximate "center" time of the flash
episodes was 4:34UT Aug 16th. from my location on the West Coast.  I
watched with 8x50 binocs until the flashes became invisible at around
4:41UT.

The next night, the geosat was reacquired and more precise flash timings
and positional measurements made.  I was able to determine the
satellites flash period as 29.24 seconds between major flashes, with the
secondary or "alternate-panel" flashes 1/2 way between.  As with
Superbird-A, one set of panels was the brighter at first, with a slow
change in maximum brightness to the other set of panels.  For a period
of approximately 2 minutes, the flashes appeared about equal in
brightness. with occasional flashes near 1st magnitude - easily 2nd
magnitude.  One measured interval was 2min 26.21sec between major
flashes (5 periods) yielding the stated 29.24 second flash rate.
Maximum brightness period was at 4:41UT. +/- 1 minute on Aug 17th UT.
The last observable flash in binocs was at 4:50UT.  For the West Coast
therefore, the maximum brightness flashes are occurring about 8-9
minutes later each night.

The geosat's position was  RA 17h52m21s, Dec -618'42" on Aug 17th at
4h36m40s UT to an accuracy of about 0.05 degree.  There was very little
N-S movement, indicating a near-equatorial (0-degree inclination)
geosat.  This position is just NW of Tau (69) Ophiuchi. 

believe I found the culprit  --  TDF 1  (NORAD 19621 or  88 98A)  It
matched position and track exactly.  I invite others more experienced
than I to confirm this from the data I've given above.

Has anyone else seen this satellite?  VERY similar to Superbird-A and
VERY easy to observe the flashes naked-eye even from light-polluted
skies.  More observations would be needed to nail down the rotational
axis for future maximum flash period predictions, but that is beyond my
expertise.  


Rick Baldridge
rbaldridge@filss.com
(408) 562-2893 days
N37.272, W121.977  Campbell, CA USA