Re: Decay update: Molniya 3-48 r

Alan Pickup (
Sun, 12 Jan 1997 11:40:48 +0000

In message <>, which took an
inordinately long time to be reflected on SeeSat-L, Alan Pickup
<> writes
>... it was running all of 40 seconds earlier than my
>prediction of a few hours ago; the uncertainty must have been greater
>than I thought and the decay will be sooner. Taken alone, this elset
>evolves to decay at January 11.8, but yet another analysis (using elsets
>since January 10.58) suggests that decay may occur at January 12.66
>(~15.20 UT).

Oh dear, I meant January 11.66 as my SatEvo output made clear (I hope!).

Mike McCants has posted later elsets but not this one, released after his
Molniya 3-48 r   7.5  2.6  0.0  5.3 d            145 x 130 km
1 24641U 96060B   97011.68079513  .28457703  90213-5  26505-3 0  1815
2 24641  62.7758 213.2859 0011962 112.6382 247.5773 16.50697726 12553

I believe it decayed on this rev, possibly near or shortly after the
perigee at January 11.70.

The question arises as to what went wrong with my prediction late on the
10th that this would "decay at about January 12.02 but this is still
uncertain by one or two orbits". That prediction had been based on elsets
from Jan 9.84 to Jan 10.70. What I didn't appreciate until later was that
there had been the strongest geomagnetic storm since October 23 between
Jan 10.25 and Jan 10.5. There are good reasons to believe that the
atmospheric density (and therefore drag) at low altitudes increased
substantially as a result of this event. For example, OIG's ndot/2 for
both #23852 = MSX Delta r (perigee at 190 km) and #24702 = Bion 11 SL-4 r
(210 km) increased by about 60% during the hours following Jan 10.5 (and
is still elevated) as compared with the (pretty stable) average over the
previous 3 days. Though both objects are approaching decay in the next
month, I'd expect to see their ndot/2 increasing at only 3.5%/day or so,
much less than that observed. I suspect the increased density as a result
of the storm is what brought #24641 down early.  Of course, SatEvo does
not (yet!) predict geomagnetic storms :-(

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