Bob King wrote: > I've been plugged into this wonderful network for a long time but have > rarely submitted an observation. Tonight I did see Shenzhou-7 using > Heavens Above. It was on track -- passing just south of Jupiter -- but > about a half-minute earlier than the prediction. It was 3rd magnitude > and moving quickly. I waited to see the rocket stage but nothing. I > have a photo of the pass if anyone is interested. My question: did I > see the rocket stage or the ship itself? Thanks for your help. Based on the latest Space Track elements, the rocket should have passed a few degrees below (i.e. south) of Jupiter on Sep 26 near 01:10:12 UTC; Shenzhou 7 should have passed several degrees above Jupiter, near 01:15:20 UTC. Since your object passed to the south of Jupiter, it must have been the rocket. I suspect the explanation for its apparent half minute early arrival relative the H-A prediction, is that you ran your prediction when H-A was still using the initial Space Track elset of the payload (08047A / 33386), of epoch 08269.5963, when it was in its elliptical parking orbit. Its circularization manoeuvre on Sep 25 near 20:03 UTC invalidated that elset. The rocket of course remained in nearly the same elliptical orbit as Shenzhou had occupied prior to its manoeuvre, but with a 5 km lower apogee, due to the effect of its separation motors at the time of spacecraft separation, about 10 min after launch. The lower apogee caused it to arrive about half minute earlier than Shenzhou 7 would have, had it not circularized its orbit, thus accounting for the apparent time discrepancy between prediction and observation. You have a reasonably good Shenzhou 7 pass tomorrow night, so perhaps you will still be able to observe it. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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