Unexpected Iridium monster flare

Frank Reed (f-reed@metabien.com)
Mon, 18 May 1998 16:34:42 -0700

My wife and I were watching for a mag. -7 flare from Iridium 4 predicted by
the GSOC web page for 17 May 1998, 19:49:09 local Arizona (mountain
standard) time (02:49:09 18 May 1998 UTC) at 111.898 W, 33.484 N.

We saw a flare of the expected brightness that peaked about 10 seconds
before the prediction.  Then, as I had my head down looking at my stopwatch
and notes, my wife said "Oh, there's another one!"  I looked up and saw
another flare at about the same magnitude, this one at the predicted time.

To investigate, I ran SatSpy and found that Iridium 5 was about 50 seconds
ahead of Iridium 4 in a similar orbit.  The TLEs used were:

1 24795U 97020D   98126.11093299 -.00000045 +00000-0 -21871-4 0 01913
2 24795 086.4138 356.0696 0003321 030.4032 329.7335 14.36937212052507
1 24796U 97020E   98126.08880101 +.00000023 +00000-0 +10146-5 0 01879
2 24796 086.4010 356.1387 0003620 111.3746 248.7827 14.34219133052462

as downloaded from OIG a few days ago.

I believe the first flare was Iridium 5, and the second was the predicted
Iridium 4 flare.  The first flare was observed a few degrees to the south
of the second, which is consistent with the sky plots for the two

There have been numerous messages in this mailing list about failure to
observe predicted flares and a few messages about unexpected observations
of flares from Iridium 5.  

I have copied many (if not all) of these messages to a text file which I
will be happy to email to anyone upon request.  I didn't post the file to
this mailing list because it is fairly long - about 20K bytes, but will do
so if requested.

I suspect that the attitude of the satellite is a little bit out of
tolerance, but haven't tried to confirm/refute this from the data in the
reports mentioned above.

- Frank