Re: Incorrect prediction for Iridm 15 Dlt r

Tyler MacKenzie (mackentd@is.dal.ca)
Thu, 19 Mar 1998 00:20:22 -0400 (AST)

Gregory May wrote:
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On Monday evening I observed this VERY fast-moving object.

Actually, I was lucky to have caught sight of it, because it was
approximately 50 seconds EARLY, according to the prediction generated by
SatSpy v2.5 (3/16/98  19:49:56). 
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I have been waiting for good passes of this rocket; I too saw it Monday,
though I didn't try timing it until Tuesday evening (19:19 pass, with 1/2
degree of overhead, at mag 2.2 [SatSpy pred.s]). I used a tape recorder,
Tag Heuer watch, binoculars and laid down beside a satellite weather
downlink antenna on the roof of oceanography that I know the position of
within 2 meters. I used the dklist.tle elset for 18-march afternoon and
advanced it with SatEvo0.29 to epoch 98077.011 UT (about an hour before
pass) as:

Iridm 15 Delta r 5.9  2.4  0.0  5.6 d            324 x 222 km
1 24874U 97034F   98077.01087471  .00620793  12659-3  84331-3 0 92769
2 24874  82.7033 288.5154 0076326 134.2650 226.3637 16.00554248 39172

After going through the tape, I figured it to pass 8.7 +/- 2.3 seconds 
(95% confidence interval) EARLY. I should have taken more time points for
a better regression and error determination, but the tape speed was
surprizingly more variable than expected. HINT: use an external microphone
in cold weather and keep the delicate recorder in a warm pocket.
Anyway, it's a beautiful object I hope more people can get to see,
-tyler

Tyler (Joe Stats) MacKenzie
Department of Oceanography, Dalhousie University, Halifax, Canada
http://www.geocities.com/CapeCanaveral/Hangar/5918/
44.636N 63.595W 50m ASL