Updated 96072B elements

Ted Molczan (molczan@fox.nstn.ca)
Wed, 15 Jan 1997 11:16:39 -0500

Here is Pierre's latest update:

USA 129 r        9.8  3.0  0.0  3.0 v
1 24681U 96072  B 97 13.53835740  .01510046  00000-0  21818-3 0    03
2 24681  97.6155  80.7653 0419000  86.4625 278.3191 15.45676063    04

On 15 Jan, at about 12:00 UTC, an uncertainty of 50 percent in the
ndot/2 would result in a 2.7 minute prediction time uncertainty, 
assuming the remaining elements are accurate. By the same time on the
16th, the uncertainty increases to 6.1 min. I strongly believe that
the real uncertainty is much less, but usually it does not hurt to 
allow more time.

This object has not been seen on the past couple of days, despite
observers looking at the correct time. For example, this elset
predicted a pass on 14 Jan for Rob McNaught at about 12:00 UTC, and
he observed between 11:45 and 12:05, but saw nothing. This was by no
means an excellent pass, but quite doable. One possible explanation
for the sudden invisibility might be found in a recent comment from
Bjoern Gimle in a SeeSat-L post on 12 Jan:

>Ted, Pierre and others have expressed surprise at the low decay rate
>so far, and Pierre's elsets have been very consistent since 97001.58,
>so there is no reason to suspect the perigee height is in error.
>My interpolation of his MM gives ndot/2 increasing from 0.00898 to
>0.01087 on Jan'09, closely matching the elsets, and Bstar for SGP4
>model probably matches those.
>With these elsets, and a standard atmosphere, I have estimated an
>average area/mass ratio of 0.0039 m2/kg. Disregarding the possibility
>of a heavy payload still attached to the rocket, this would mean
>that the rocket has been aligned along the direction of motion, at
>least near the perigee. But the flashing/variation observed should
>indicate there was some rotation.
>Except for this question, the higher decay rate should indicate  that
>the rocket finally is showing its average area in the direction of
> motion, and this should hopefully be apparent in the visual 

If the object's long-axis was initially oriented in the direction of 
flight, then that would account for between about 0.5 and 1.0 mag of 
its 1.9 mag of "excess" brightness. Those are theoretical values, based 
on only on dimensions - it could conceivably account for all of the 
observed difference in brightness.

If so, then the abrupt increase in decay rate may well be associated 
with a 2 mag, or so, decrease in brightness, making the object much 
less easy to spot than before, especially on marginal passes. I agree 
that the observed slow rotation does not quite add-up in this hypothesis, 
but I can think of no better explanation at the moment.

Clear skies!