Iridium 21 (97-34E, #24873) -- NO FLARE!
Ed Cannon (ecannon@mail.utexas.edu)
Thu, 23 Oct 1997 21:07:45 -0400
Warning! Some of the current Iridiums apparently are not
reliable flare/glint/flash producers.
We had a prediction for a -1 flare from Iridium 21 (97-34E,
#24873) tonight in central Austin, and Mike McCants and
family drove about 24 km (15 miles) east to observe it from
near the predicted center line (which Mike calculated using
another program). Sue Worden was observing it from some
kilometers north of my location. No flare, no glint, no
flash, no nothing was observed by any of us (except that
Mike said he saw a couple of satellites in binoculars).
After the fact I examined my current Iridiums elements (all
epochs 97294 or later, and I noticed that Iridium 21is in an
anomalous orbit with a mean motion of 14.779 instead of the
operational 14.342. Upon further examination, I see three
others also in anomalous orbits. So the following four
apparently are not reliable as to predicting flares:
Cat # COSPAR Ir MeanMo
24842 97-30G 11 14.392
24873 97-34E 21 14.779
24947 97-51D 27 15.035
24967 97-56C 36 15.034
I suggest that everyone cross-check their flare predictions
with the above list. Perhaps the prediction program writers
will be able to incorporate some sort of "unreliable" flag
based on mean motion or other anomalous elements in future
versions of the programs, just as a favor to observers who
forget to verify ahead of time that a prediction is not for
one of the unreliable ones.
On the positive side, Mir, Seasat (78-64A, #10967), and UARS
(91-63B, #21701) all had good passes here this evening. UARS
seemed almost to retrace Seasat's track, but in the opposite
direction! UARS also flashed briefly to mag. 0 very early in
its pass.
Ed Cannon
ecannon@mail.utexas.edu
Univ. of Texas at Austin, USA -- 30.29N, 97.74W, 152m