Iridium 21 (97-34E, #24873) -- NO FLARE!

Ed Cannon (
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
Univ. of Texas at Austin, USA -- 30.29N, 97.74W, 152m