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