Welcome to the list Rodney. I remember observing the third comet you discovered, 1989 X1, early in May 1990. > Observing site: Huirangi Cemetery, Taranaki, New Zealand. > Lat -39.05, Long 174.27 East > > Time: 0335 am New Zealand Daylight Saving = 14:35 UT 12 January > > Very bright satellite (approx mag -3) passed between Alpha > and Beta Centauri moving NNW. Altitude approximately 35 > degrees, in the South East. > > Rate of motion approx 1 degree in about 4 seconds. > > It had all the hallmarks of an Iridium flare. It was starting > to fade when I first noticed it. Faded rapidly to about 3rd > magnitude and stayed at that brightness for a further minute > at least before dropping rapidly from sight. The orbital plane of USA 116 (23728 / 95066A), a KeyHole imaging reconnaissance satellite, is roughly consistent with Rod's observation. The optical behaviour he observed is very consistent with this type of satellite, as was the direction of travel and angular velocity. The last reported observation of USA 116 was on 2004 Dec 14, by Greg Roberts. Based upon its orbit at that time, and assuming that his site coordinates are accurate to near the stated precision, Rod should have seen it pass well below Alpha and Beta Centauri, at about 14:33:16 UTC, nearly 2 min earlier than the object he reported. However, if USA 116 performed a re-boost manoeuvre in the interim, then that could account for different time and track. A small reboost could easily account for the 2 min late arrival, but would have been insufficient to account for the higher elevation track, so it had to have been fairly large. Keyholes typically make their largest manoeuvres when their perigee is near either an ascending or descending node, i.e. over the equator, either north or southbound. It so happens that the perigee precessed southbound over the equator on 2004 Dec 26, so a large manoeuvre could have been performed +/- several days of that date. USA 116's plane was near apogee and to the east of Rod, so some combination of an increase of its apogee height and a westward shift of its ground track is required to account for the observed track. Keyhole reboosts have exactly that effect. They manoeuvre at perigee to boost their apogee, and the increase in altitude reduces the eastward rate of precession. I have constructed an arbitrary search orbit, assuming reboost on 2004 Dec 26 near 14:59:00 UTC, at the 12.75 W descending node: USA 116 15.0 3.0 0.0 5.1 v 1 70000U 04361.62430557 .00001500 00000-0 84896-4 0 01 2 70000 97.8275 127.4224 0340500 181.0369 0.0000 14.75107169 00 This orbit agrees well with Rod's observation last night, putting the track roughly midway between Alpha and Beta Centauri, at 14:35 UTC. That USA 116 has manoeuvred must be considered as highly speculative, so it would be wise to attempt to re-acquire it in its last known orbit before spending too much time on a planar search of the above orbit. For anyone contemplating a planar search, I estimate that 24 h past epoch, the prediction time uncertainty of the search orbit is roughly +/- 7 min. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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