Decay watch: July 3

Alan Pickup (alan@wingar.demon.co.uk)
Sat, 3 Jul 1999 10:47:05 +0100

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Object: #25670 = 99- 17 B = DSP 19 Titan 4 r

As I indicated yesterday, further elsets appeared showing that this 
survived beyond SpaceCom's declared decay time of July 1 19:55 
(+-1 minute!). Here are the final five published elsets:

DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         199 x 132 km
1 25670U 99017B   99182.34500781  .09354617  00000-0  19070-3 0  1664
2 25670  28.6057  38.9987 0050564 319.2261  40.5101 16.40158972 13006
DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         179 x 113 km
1 25670U 99017B   99182.70919047  .10142068  00000-0  67670-4 0  1671
2 25670  28.6080  36.0474 0050529 324.2131  35.5633 16.47596114 13066
DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         152 x 114 km
1 25670U 99017B   99182.76962001  .17244808  00000-0  92817-4 0  1689
2 25670  28.6032  35.5165 0029192 335.8368  24.1413 16.52332186 13070
DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         176 x 117 km
1 25670U 99017B   99182.82993805  .06460487 -73803-5  50038-4 0  1690
2 25670  28.6234  35.0602 0045247 339.3738  19.0193 16.47363146 13054
DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         159 x 112 km
1 25670U 99017B   99182.89087212  .49683666 -75085-5  26589-3 0  1705
2 25670  28.6194  34.7790 0036179  44.5503 315.5816 16.51489482 13066

SpaceCom's decay time was just prior to the epoch of the penultimate
elset. Note, however that the mean motion and drag for this elset are
both lower than for the elset two orbits before. Similarly, the final 
elset has a lower mean motion (but higher drag) than the one for two 
orbits before. Also, as I have suggested before, the perigee height
shows an unfeasibly large drop between the elsets for 99182.34 and
99182.70. Finally, there is something odd about the shift in perigee
around the orbit between the final pair of elsets.

My normal analysis, attempting to fit a SatEvo orbital evolution 
through the elsets, is impossible or unsatisfactory for this set of 
elsets. It is clear, though, that SpaceCom was having trouble too -
hence the odd behaviour of perigee and mean motion. This despite the 
fact that this was one of the larger objects, and presumably 
strongest signals, being tracked.

I wonder whether the problem, in fact, was the size of the rocket and
its susceptibility to the effective decrease in drag coefficient as 
its perigee fell through the atmospheric flow transition level at 
about 133 km (for an object of this size). Without this effect, 
the decay would have been roughly in line with SpaceCom's predictions 
(and conclusion). With the effect, the lifetime would be extended by
a few hours. I suspect that this is what transpired.

So when did it really decay? The first of the five elsets above is 
last one with which I have much confidence. Adjusting the mean motion 
and drag for this, I have derived a SatEvo evolution that satisfies
six elsets over the preceding 9 hours with a maximum residual of 0.5
second, and leaves a residual for the equator crossing time of 
SpaceCom's final elset of 1.1 sec. This evolution ends...

DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         151 x 117 km
1 25670U 99017B   99182.89088587  .18639804  23408+0  10846-3 0 91660
2 25670  28.6036  34.5993 0026735 326.3767  33.4539 16.52045522 13099
DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         142 x 113 km
1 25670U 99017B   99182.95124292  .24557119  44680+0  10827-3 0 91660
2 25670  28.6032  34.1073 0022247 327.1765  32.6855 16.54613472 13102
DSP 19 Titan4r  10.0  2.5  0.0  3.0 d 31         128 x 107 km
1 25670U 99017B   99183.01149033  .39391497  14914+1  11638-3 0 91668
2 25670  28.6026  33.6140 0016292 327.9783  31.9228 16.58282732 13117

I estimate that decay would have occurred near perigee on the last
of these orbits, at July 2 01:41 UTC near 4.2 S latitude, 80.6 E 
longitude while ENE-bound over the Indian Ocean.
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Object: #12133 = 81-  2 A = Molniya 3-14

Decay predictions:
Source   Prediction made    Predicted decay at      Latitude Longitude
               UTC                UTC                  deg      deg

SpaceCom   Jun 29 16:23     Jul  3 16:02 +-2d        43.6 S   179.8 E
SpaceCom   Jul  1 08:52     Jul  3 00:37 +-1d        15.8 S    75.5 E
SpaceCom   Jul  2 19:44     Jul  3 18:31 +-14h       14.7 S   164.8 E
SpaceCom   Jul  3 06:32     Jul  3 16:37 +-6h        41.8 S   173.0 E

SatEvo     Jun 29 19:10     Jul  4 01:22 +-1.2d
SatEvo     Jun 30 18:45     Jul  3 19:22 +-20h
SatEvo     Jul  1 22:45     Jul  4 00:59 +-18h
SatEvo     Jul  2 23:00     Jul  3 21:20 +-8h        58.7 S    67.9 E
SatEvo     Jul  3 09:40     Jul  3 18:08 +-4h        59.7 S   112.7 E

Latest elset (127 sec early against an extension of yesterday's 
prediction):
Molniya 3-14                                     1403 x 83 km
1 12133U 81002A   99184.23725705  .99999999  90508-5  96570-3 0  2670
2 12133  61.9086  12.9469 0926803 282.3356  67.4644 14.44761874 50350

SatEvo prediction:
Molniya 3-14                                     1014 x 80 km
1 12133U 81002A   99184.50936678 1.41555722  88244+0  91770-3 0 92677
2 12133  61.8838  12.0264 0674132 282.4426  70.1006 15.06410948 50391
Molniya 3-14                                     595 x 78 km
1 12133U 81002A   99184.70488793 2.56305518  45635+1  10415-2 0 92676
2 12133  61.8599  11.2985 0385040 282.5285  73.1922 15.78002520 50423

Note: I predict decay near perigee on the latter orbit, over the
Southern Ocean, SW of Australia. SpaceCom has it one orbit earlier.
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Alan
-- 
 Alan Pickup | COSPAR 2707:  55d53m48.7s N  3d11m51.2s W   156m asl
 Edinburgh   | Tel: +44 (0)131 477 9144     Fax: +44 (0)870 0520750
 Scotland    | SatEvo page:   http://www.wingar.demon.co.uk/satevo/