Iridium 24871 tumbling; plus other Iridium obs

Ed Cannon (ecannon@mail.utexas.edu)
Sun, 07 Jun 1998 02:55:53 -0500

Saturday evening (about 4:36 Sunday 7 June UTC), Mike McCants and I 
observed an Iridium, #24871, very obviously tumbling rapidly, about
mag. +5.5.  It was easy to see using Mike's finder scope.  However,
my recollection is that neither of us saw any bright flashes from 
it; these were just ordinary maxima.

I'm not 100% sure what its correct ID or common name are.  Below are 
some elsets for comparison.  It's definitely the one with slightly 
higher mean motion (and lower orbital altitude).  Alan Pickup and 
Mike agree below that it's Iridium 20, 97-34C; OIG is still calling 
it 18.  

We also observed Iridium, #24872, and it did not display anything
unusual.  Mike and Alan agree below that this is Iridium 18 (97-34D); 
OIG is still calling it Iridium 20.

>From OIG Web site:

IRIDIUM 18
1 24871U 97034C   98156.14126553 +.00000184 +00000-0 +58259-4 0 01955
2 24871 086.4000 046.7386 0014659 096.7807 263.5066 14.34522202047507
IRIDIUM 20
1 24872U 97034D   98156.73671225 -.00000138  00000-0 -56337-4 0  1622
2 24872  86.3996  46.4950 0003939 121.9210 238.2362 14.34217366 47558

>From OIG telnet site:

Now cross-referencing the following SATELLITE CATALOG numbers:
24871
24872

CATALOG NUMBER            INTERNATIONAL DESIGNATION
SATELLITE NUMBER 24871 WAS NOT FOUND.
SATELLITE NUMBER 24872 WAS NOT FOUND.

>From Alan's iridiums.tle file:

Iridium 20 att   3.0  0.0  0.0  6.0 d            787 x 766 km
1 24871U 97034C   98156.14126553  .00000184  00000-0  58259-4 0  1955
2 24871  86.4000  46.7386 0014659  96.7807 263.5066 14.34522202 47507
Iridium 18       3.0  0.0  0.0  6.0 d            781 x 775 km
1 24872U 97034D   98156.73671225 -.00000138  00000-0 -56337-4 0  1622
2 24872  86.3996  46.4950 0003939 121.9210 238.2362 14.34217366 47558

Mike's iridium.html file:

Iridium 20 att
1 24871U 97034C   98156.14126553 +.00000184 +00000-0 +58259-4 0 01955
2 24871 086.4000 046.7386 0014659 096.7807 263.5066 14.34522202047507
Iridium 18    
1 24872U 97034D   98156.73671225 -.00000138  00000-0 -56337-4 0  1622
2 24872  86.3996  46.4950 0003939 121.9210 238.2362 14.34217366 47558

Besides those two, we also saw in twilight a *really* bright flare, 
as predicted, from Iridium 53; we saw Iridium 11 do some very bright 
flashes; and we saw Iridium 21 (24873, 97-34E), a non-operational 
one stuck in the parking orbit, but it appeared steady and not very 
bright.

Additionally, Saturday morning (6 June) I observed a flare from 
Iridium 32; it was fainter than predicted (Iridflar -7, GSOC -5) as 
compared to Jupiter, which was several degrees above it, but there 
was definitely some haze, and it was only 20 degrees above the 
horizon.  I also watched Iridium 27 display 3 episodes of very bright 
flashes (much brighter than Iridium 32) at approximately UTC 9:39:30 
(two flashes), 9:42:45 (two flashes), and 9:43:19 (several flashes), 
plus-or-minus a second or two.

Ed Cannon
ecannon@mail.utexas.edu
Austin, Texas, USA