iridium flares

richard.keen@kingsmarket.com
Tue, 03 Mar 98 18:41:52

                                  
 Flare-watchers -
 Certainly not having an Iridium Flare drought here in Colorado, USA!
 Here's the Iridflar (verson 1.5) output, with my estimated magnitudes
following:
 Ir  Date    Time    Az  El Range  Sun Flare  Vis Peak  Std  Obs
            MST(UT-7)         km  elev Angle  Mag  Mag  Mag  Mag
 38 98-2-22 19:46:53 017 27 1433 -23.4  0.87 -0.4 -7.3 -1.4  0 thru cloud
 20 98-2-22 19:48:13 016 28 1424 -23.6  0.39 -3.2 -7.3 -4.2  -5 thru cloud
 52 98-3-1   5:02:30 193 43  913 -18.0  0.00 -8.3 -8.3 -8.3  3
 10 98-3-1   5:09:30 202 37 1182 -16.6  6.30  4.1 -7.8  3.7  4
 11 98-3-1  17:36:55 221 33 1248   2.5  0.28 -4.5 -6.8 -6.0  not visible
 21 98-3-1  18:51:13 014 50  804 -11.3  0.27 -6.4 -8.5 -6.2  not visible
 20 98-3-1  19:13:59 015 41 1113 -15.7  0.60 -2.1 -7.8 -2.5  -4
 39 98-3-2  19:07:47 013 43 1082 -14.6  0.10 -7.8 -7.9 -8.2  -6 thru Cirrus
  9 98-3-3  17:05:48 343 80  789   8.6  0.04 -8.3 -8.3 -8.3  -7 naked eye
 I just observed the last flare a few minutes ago, and by lining up the
predicted position with a point on the roof edge and lying down on the deck,
it was easy to spot.  It was only visible for about 2 seconds.
 Note that some of predicted flares were way off on magnitude.  In particular,
the predicted mag. -8 flare of Iridium 52 could only must mag. +4, but that's
probably because I was using 2-day-old elements and the object is still rising
to it's final orbit.  Then there's the "rogue" objects, Iridiums 11 and 21.  I
think I should have able to spot the mag. -4.5 Iridium 11 flare with 7x50
binoculars, despite the sun being just above the horizon.  Meanwhile, nothing
was visible of the predicted mag. -6 Iridium 21 flare!
 I think one may conclude that Iridium objects that have reached their final
orbit, with Mean Motion of 14.342, should be reliably predictable, while other
objects are either being moved to that final orbit, or are having other
problems.  So, from Mike McCant's CS980226 file, here's a list of Iridium
satellites with Mean Motions NOT 14.342:
 Iridium Epoch   Mean Motion
 Ir 24   98057   14.337
 Ir 5    98056   14.370
 Ir 18   98057   14.370
 Ir 48   98057   14.371
 Ir 38   98057   14.372
 Ir 42   98057   14.375
 Ir 11*  98057   14.391
 Ir 50   98057   14.508
 Ir 56   98056   14.532
 Ir 53   98057   14.538
 Ir 54   98057   14.682
 Ir 52*  98057   14.738
 Ir 21*  98057   14.780
 Ir 27   98057   15.039
 Cheers, Rich Keen
 Coal Creek Canyon, Colorado, USA (39.877 N, 105.391 W, elevation 2728m)