Decay watch: May 16 (Delta 2 post-mortem)
Alan Pickup (alan@wingar.demon.co.uk)
Sun, 16 May 1999 11:15:56 +0100
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Object: #25347 = 98- 32 F = Iridium 70 Delta 2 r
Decay predictions:
Source Prediction made Predicted decay at Latitude Longitude
UTC UTC deg deg
SpaceCom May 11 17:34 May 15 18:01 +-2d 18.5 S 124.9 E
SpaceCom May 12 19:49 May 15 18:13 +-2d 60.8 S 163.8 E
SpaceCom May 13 13:36 May 15 13:25 +-9h 19.8 S 69.2 E
SpaceCom May 14 15:01 May 15 15:25 +-15h 26.7 S 146.2 W
SpaceCom May 15 05:28 May 15 15:48 +-7h 63.7 N 136.7 W
SpaceCom May 15 09:26 May 15 15:47 +-5h 61.4 N 137.8 W
SpaceCom May 15 13:25 May 15 15:38 +-2h 23.6 N 143.8 W
SatEvo May 9 14:25 May 15 18:00 +-1.5d
SatEvo May 12 18:20 May 15 17:42 +-15h
SatEvo May 13 19:20 May 15 11:41 +-9h 30.0 N 88.7 E
SatEvo May 14 18:50 May 15 11:49 +-5h 0.0 90.1 E
SatEvo May 15 10:30 May 15 14:05 +-2h 16.1 N 122.4 W
SatEvo May 16 08:00 May 15 14:24 +-30m 82.1 N 3.5 E
Final elsets:
Iridm 70 Delta r 5.9 2.4 0.0 5.6 d 156 x 147 km
1 25347U 98032F 99135.46280069 .11948106 -16080-5 31496-3 0 4739
2 25347 84.0798 320.0917 0007234 52.7192 308.0497 16.45374817 56269
Iridm 70 Delta r 5.9 2.4 0.0 5.6 d 151 x 139 km
1 25347U 98032F 99135.52344543 .15514774 -16886-5 24458-3 0 4743
2 25347 84.1073 320.0661 0009110 356.6314 3.4627 16.48001220 56279
Note: The final elsets show the rocket running only 0.8 second early
and 0.2 second late respectively against the SatEvo prediction in my
previous posting. SpaceCom has yet to release a post-decay report
for this and it is possible that there may be a further elset.
While the drag (ndot2) terms above may be consistent with SpaceCom's
decay time, they are certainly too low and *in*consistent with the
changes in mean motion implied by the same elsets. For example, the
increase in mean motion between the two elsets implies that the drag
over that interval averaged 0.2165 and, since it would have been
increasing during that period, should have been even higher at the
epoch of the final elset and not the 0.155 reported. This behaviour
(SpaceCom underestimating the drag near decay) is par for the course.
A further SatEvo analysis, satisfying exactly the equator crossing
times implied by the final three elsets, leads to the following elset
for the start of final orbit:
Iridm 70 Delta r 5.9 2.4 0.0 5.6 d 125 x 122 km
1 25347U 98032F 99135.58401075 1.18765927 19592+2 60760-3 0 94720
2 25347 84.0918 319.9876 0001984 25.2507 334.7590 16.56008306 56286
The track took it northbound just E of San Francisco at 14:10 UTC
towards decay near northern apex. It might have decayed near to
the beginning of the orbit, or it might have survived as far as the
following southbound equator crossing near 46 deg E longitude at
14:44 UTC.
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Alan
--
Alan Pickup | COSPAR 2707: 55d53m48.7s N 3d11m51.2s W 156m asl
Edinburgh | Home: alan@wingar.demon.co.uk +44 (0)131 477 9144
Scotland | SatEvo page: http://www.wingar.demon.co.uk/satevo/