Ir 71, Ir glints, analysis, average interval

Walter Nissen (dk058@cleveland.freenet.edu)
Mon, 27 Jul 1998 13:49:07 -0400 (EDT)

OBS: 
 
Ir 71 was finally well seen, on a nearly zenithal pass, and displayed 
flashes apparently diagnostic of her failure.  I picked her up below left 
of Sabik = eta Oph, far to the South, and followed her past culmination, 
losing her soon after to dimness at mag 7? or so, tho I suspect my 
tracking in "invisible mode" was ok for probably a minute after dis.  With 
a nominal uncertainty of .5 s, I recorded bright, brief flashes: 
Ir 71 mag 3?           F        19980727  23209.19 
      mag 3?           F        19980727  23234.38 
      mag 4?           F        19980727  23259.21 
      mag 0?           F        19980727  23312.87 
and lost her maybe 20? s later.  Only the 4 flashes were seen, her 
appearance in the South being normal for an Iridium. 
 
Ir 26 located, mag 3?           19980727  33447.79 
      mag 1?       glint        19980727  335 2.83   dimmed extremely slowly 
      dimmed more definitely    19980727  33519.38   smoothly dimmed to 
      mag 5?                    19980727  33536.89 
 
The implication being that if I didn't locate it until mag 3?, it may have 
brightened quite rapidly. 
 
Ir 69 located, mag 5?           19980727  34349.68   quickly began 
                                                     brightening smoothly 
      mag 0 or 1   glint        19980727  34416.19   dropped smoothly, rapidly 
      reached mag 5?            19980727  34426.96   later mag 5? to 7? 
      lost                      19980727  34452.66 
 
Flat maxima, PPAS code: M, are quite difficult to judge. 
 
Having seen enough of these glints to activate my pea brain, I now 
perceive a few things.  My OBS have evolved toward capturing more detail, 
but the earlier OBS are consistent in some ways with patterns that still 
persist.  Paul Maley and Rob Matson have probably seen enough of these 
reports to notice that I have repeatedly reported an initial double glint 
followed 9 minutes later by a single glint.  In fact, I assert that my OBS 
last night are very consistent with that pattern.  I almost saw a double 
glint of Ir 26.  Not quite, but close.  I agree with their suspicion that 
further analysis of detailed OBS may reveal a correlation between the 
shape of the Iridial objects and the light curves observed, including the 
occurrence of double and triple glints.  I am interested in making 
detailed OBS of single glints as well, but perhaps I could predict which 
glints will be double.  Perhaps you can, too. 
 
The mean motion of the Iridia is 14.342172 revolutions per day. 
 
A recent file, from Alan Pickup, latest epoch date 98207.37889661, gives 
72 Iridia, 64 with mean motions clustered between 14.34212985 and 
14.34222731.  Discarding the bottom 5% and top 5% as oddball outliers, 
just on general principles, the median MM of the remaining 58 Iridia is 
14.34217268, and the mean MM is 14.34217189.  Choosing one of these as an 
average, the average period is 100.40320 minutes (6024.1920 s for us SI 
fans) and the average interval between successive passes, or glints, I 
suppose, for the 11 operational satellites in each orbit is 9m 7.65381s = 
547.65381 s.  Empirical experience is highly consistent with these 
calculations.  The Iridia orbit in a highly regular geometrical pattern. 
 
 
PPAS(beginning): 
98- 26 B 98-07-27  2:32: 9.2 WN   25.2  .5   1   25.2  FF', Iridium 71 = 25320 
98- 26 B 98-07-27  2:32:34.4 WN   24.8  .5   1   24.8  FF', Iridium 71 = 25320 
98- 26 B 98-07-27  2:32:59.2 WN   13.7  .5   1   13.7  FF', Iridium 71 = 25320 
97- 82 B 98-07-27  2:46:47.3 WN    7.1  .5   1    7.   FF', Iridium 24/46 = 
                                                       25105 
 
Cheers. 
 
Walter Nissen                   dk058@cleveland.freenet.edu 
-81.8637, 41.3735, 256m elevation 
 
--- 
 
Darkness has its place -- in the night sky.  Look into it. 
 
--- 
 
Details: 
Latitude:  41.37350  Longitude:  -81.86370  Altitude:  256.0 m 
Time Zone: UTC  +0.0 h 
                      Iridium Coordinates  Range   Sat   Solar                Peak  Std    Maximum Flare 
Ir   Date      Time    Azm El   RA   Decl  (km)  N Ill Azm  Elev M FlrAng Mag  Mag  Mag Latitude Longitude 
26 98- 7-27  3:34:57.0 249 20 14h20  -1.7 1747.9 A Lit 329 -22.8 F  2.43  2.9 -6.7  1.3  41.0162  -80.6539 
26 98- 7-27  3:35:11.2 252 21 14h14   1.1 1703.6 A Lit 329 -22.8 F  0.95  0.4 -6.7 -1.1  41.5962  -80.8796 
26 98- 7-27  3:35:25.0 256 22 14h08   4.0 1664.8 A Lit 329 -22.9 F  2.50  3.0 -6.7  1.4  42.1722  -81.0659 
 
69 98- 7-27  3:43:55.0 250 16 14h13  -3.8 1963.1 A Lit 331 -23.7 F  2.15  2.9 -6.4  1.0  40.5235  -82.7023 
69 98- 7-27  3:44:09.6 253 16 14h08  -1.2 1916.1 A Lit 331 -23.7 F  0.89  0.5 -6.4 -1.3  41.1059  -82.9704 
69 98- 7-27  3:44:24.0 256 17 14h03   1.4 1873.9 A Lit 332 -23.7 F  2.22  2.9 -6.4  1.1  41.6956  -83.1948 
 
reformatted to conform to my one-line QuickSat output: 
       H  M  S  TIM AL AZI C   U  MAG SHD  RNG  R A   DEC 
       3 34 57   ?  20 249     A  2.9     1747 1420  -1.7  Iridium 26 -22 
24903  3 35 11   ?  21 252     A   .4     1703 1414   1.1  Iridium 26 -22  R 
       3 35 25   ?  22 256     A  3.0     1664 1408   4.0  Iridium 26 -22 
       3 43 55   ?  16 250     A  2.9     1963 1413  -3.8  Iridium 69 -23 
25319  3 44 09   ?  16 253     A   .5     1916 1408  -1.2  Iridium 69 -23  R 
       3 44 24   ?  17 256     A  2.9     1873 1403   1.4  Iridium 69 -23 
 
For predictions, from Alan Pickup: 
Iridium 26       3.0  0.0  0.0  6.0 d            780 x 775 km 
1 24903U 97043A   98206.67727318  .00000133  00000-0  40448-4 0  2250 
2 24903  86.3941 259.2664 0003210  79.2268 280.9283 14.34222731 48659 
Iridium 69       3.0  0.0  0.0  6.0 d            780 x 776 km 
1 25319U 98026A   98206.54409962 -.00000080  00000-0 -35456-4 0   661 
2 25319  86.3977 259.3095 0002412  19.2854 340.8436 14.34213221 12085 
 
Later elsets, from OIG: 
IRIDIUM 69 
1 25319U 98026A   98208.14877549 +.00000097 +00000-0 +27619-4 0 00892 
2 25319 086.3978 258.6394 0002356 017.8823 342.2474 14.34215014012313 
IRIDIUM 26 
1 24903U 97043A   98208.14241464 -.00000191 +00000-0 -75233-4 0 02332 
2 24903 086.3980 258.6550 0003106 076.8829 283.2678 14.34217978048863