Re: Relay of sat decay seen

Alan Pickup (alan@wingar.demon.co.uk)
Fri, 1 Jan 1999 20:35:10 +0000

I am not sure of the date or time of this observation, but I guess it
was seen from Florida. However, from the duration and the implied
angular velocity (2-3 seconds and ~20 deg/sec), I suspect that the
object was meteoric fireball and not a re-entry. The duration is too
short and the angular velocity too high. A more typical duration for a
re-entry observation would be 30-90 seconds, with a peak angular
velocity probably less than 5 deg/second.

It cannot have been too bright to have been a meteor since the latter
can be any brightness up to and above that of the full moon. Reflected
sunlight plays no role in the brightness. It may have been slower than a
typical meteor, but fireballs are atypical and reported durations of 2-3
seconds are not uncommon. For one thing, observers tend to overestimate
the duration of such events, while fireballs do tend to be seen for
longer than most regular (say, shower) meteors since the meteoroid
responsible is larger and more long-lived during its descent into the
atmosphere.

With regard to an "area under a decay watch", remember that it is
usually very difficult to pin-point where around an orbit a satellite
might drop. Such an area could be more than one circumference of the
Earth if the uncertainty in decay prediction is more than one orbit (as
it often is). It is possible to give general "heads-up" warnings of
possible decay observation opportunities - Rob Matson has done so from
time to time in the past. However, I concentrate on predicting the decay
time/window and (sometimes) providing predicted elsets. For me to do
more would involve more time than I can spare and would delay my timely
posting of the prediction. Given the elsets, anyone can investigate
their own chances of seeing (a) the object and/or (b) the re-entry :)

Alan
-- 
 Alan Pickup | COSPAR 2707:   55d53m48.7s N   3d11m51.2s W   156m asl
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