Thank you Harro Zimmer, for propagating the orbit of 1996-069B / 24671 to decay, using your special perturbations program - and for sharing the detailed trajectory data relative the Earth's surface, and the sky as seen from several of the Yukon eyewitness locations: http://satobs.org/seesat/May-2012/0015.html Harro has an excellent track record on SeeSat-L estimating decays, and his results are among the standards against which I evaluate my own. Harro's analysis confirms my Satana/Satevo-based finding that the final descent was in progress as 1996-069B passed within visual range of the locations of the UFO sightings, on 1996 Dec 12, from about 04:25 to 04:27 UTC (Dec 11, 8:25 to 8:27 PM PST). He estimated that during that period, the object descended from about 83 km to 68 km. I do not have the means to estimate the altitude during the final descent as precisely, but my guess of about 90 km (average) was not too far off, and the difference does not invalidate my initial report: http://satobs.org/seesat/Apr-2012/0331.html Harro's analysis adds to our understanding of the decay. Within a couple minutes after the object passed out of range of the Yukon eyewitnesses, it had descended to 30 km altitude, and lost nearly all of its forward velocity. This was at about 4:29:18 UTC (8:29:18 PM PST) over 64.88 N, 117.02 W. From that point, its descent was almost completely vertical, and Harro estimated arrival at 10 km altitude as 04:31:06 UTC (8:31:06 PM PST). The corresponding location, 64.86 N, 116.68 W, would be the approximate "toe" of any debris "footprint", where the heaviest pieces would have fallen. Most authorities that issue decay estimates, e.g. USSTRATCOM, define 10 km altitude as the point of decay. It was about 1000 km east of the zone of the Yukon sightings, but it is doubtful whether much of anything survived re-entry, so this is mostly of academic interest. Of greater interest is what more we can learn about the Yukon sightings from Harro's precise estimate of the descent. New Information The most important new information is that the final break-up probably occurred during the period of the sightings, at about the time the object came into view. Decaying objects orient themselves with the heavy end forward, like a shuttlecock, which in the case of a rocket body, exposes the engine and related structures to the greatest heat. The rocket body began to experience significant heating about 4.5 min prior to reaching Yukon, as it descended below 96 km, over the Bering Sea, just north of the Aleutians. The heating intensified as it crossed Alaska and into Yukon, but it would have remained largely intact, except for sporadic separation of debris - probably from the engine - that would have fallen behind the main object. Soon after it came into view of the Yukon eyewitnesses, the rocket body reached the altitude at which the combination of intense heat and rapid deceleration brings about the final break-up of re-entering objects, between 75 and 80 km. The sudden structural failure and disintegration would have created a swarm of bright objects. Their differing ballistic coefficients would have caused them to decay at different rates, resulting in an elongated trail of plasma and glowing pieces of debris. I had been in some doubt as to the timing of the final breakup, and suspected it to have occurred a bit after the Yukon sightings, so I am pleased to have this more precise information. To facilitate further discussion - and independent analysis - I have used Harro's trajectory data to tabulate ephemerides for several of the eyewitness locations, and to plot a few graphs: http://satobs.org/seesat_ref/96069B/Harro_Zimmer.xlsx The file opens to the first graph, which shows the change in altitude during the couple of minutes or so that the object was within range of the Yukon sighting zone. The next graph shows the altitude vs. downrange distance travelled after it passed below 100 km. It traveled about 5,000 km during this period, until its demise. Note the near-vertical descent below 40 km. The final graph shows altitude vs. time below about 100 km. The ephemerides are on the first sheet. The data is at 6 s intervals. The first five columns list the date and time - both UTC and PST. Columns 7-9 list Harro Zimmer's trajectory data, consisting of the rocket body's latitude, longitude and altitude. The remaining columns present the ephemerides for several locations of interest. The first (cols 11-14), is near the south end of Fox Lake, at the location of FOX4 and 5's sightings. Azimuth is stated in degrees clockwise from north (north is zero, east is 90 deg, south is 180 deg, etc.). Elevation is in degrees; positive values are above the horizon, which is the minimum condition required for visibility. Atmospheric extinction typically is severe near the horizon, so practical visibility begins well above the horizon. Since the sky was reportedly clear, I have assumed that the brilliant decay would have been readily visible from about 8 deg elevation and higher, which I have colour coded in green. If the conditions were exceptionally good, then visibility below 8 deg to about 5 deg might have been possible; that data is in red. The final two columns list the angular velocity in deg/s and the range in kilometres. From Fox4 and 5's vantage point, the object reached the altitude of final breakup - a little below 80 km - just as it rose above 8 deg elevation. Investigator, Martin Jasek asked both witnesses to sketch the apparent size and location of the UFO on three photographs: http://www.ufobc.ca/yukon/2212fox4,5estimates.htm Jasek reports that from top to bottom, the angular size was 12.8 deg, 8.44 deg and 3.95 deg. The mountain peak in the photo is about 8 km distant, and its azimuth is about 322 deg. The ephemeris places the decaying rocket body at that direction at about 4:25:48 UTC (8:25:48 PM PST), at just 7.6 deg elevation. Jasek reported, "FOX5 made a mental note of the time; she looked at the car clock; it was 8:23 pm.", which is in excellent agreement, as is the elevation - at least for the sketch in the top photo. In the lower two photos the object seems to be almost on the horizon or the lake itself, but the text of the report is unclear about the exact trajectory, except to say that the object headed east and disappeared behind trees. They reported seeing the object for about 1 min, which is roughly the duration it spent above about 7 deg elevation. Little wonder it was lost in the trees, given its low elevation. What is clear is that the rocket's brilliant debris trail was in the sky at about the same time and in the same direction as the UFO. Fox 3 was about 8 km north of FOX4 and 5. The ephemeris reveals about the same path across the sky, culminating a fraction of a degree higher, at 9 deg. Jasek photographed Fox3's finger pointing toward the location of the bottom of the UFO: http://www.ufobc.ca/yukon/2233fox3thishigh.htm Jasek determined "angular height of 6.5 degrees above the ground". With the aid of Google Maps, I have determined that the position was a bit west of due north. The ephemeris reports that the decaying rocket was in that direction just after 8:26 PM PST, between 8 and 9 deg above the horizon. According to Jasek, "FOX3 made a note of the time and date, it was 8:30 pm December 11, 1996 immediately after the UFO was gone." Temporal and positional agreement between the rocket body and the UFO is excellent. I will conclude this section by revisiting the report of Pelly Crossing witness PEL2, who observed the UFO pass below the Big Dipper, which she sketched: http://www.ufobc.ca/yukon/2223pel2draw1neg.htm In my initial report, I presented this computer-plotted estimate of the decay trajectory from PEL2's location, which I estimated to be accurate in elevation to within 1 or 2 deg: http://satobs.org/seesat_ref/96069B/96069B_PEL2_dwg.jpg In fact, Harrow's trajectory puts it about 3 deg lower, but the agreement with PEL2 remains excellent: http://satobs.org/seesat_ref/96069B/96069B_PEL2_dwg_2.jpg The ephemeris puts the rocket body below the Big Dipper about 8:26:30 PM PST. The time of PEL2 and 3's sighting is not known as precisely as those of Fox4,5 and Fox3. Jasek reported, "PEL3 along with his sister PEL2 left Whitehorse around 6:00 pm and therefore PEL3 reasons that it must have been close to 9:00 pm when they were arriving in the Village of Pelly Crossing." Also, "PEL2's husband arrived home from work at about 9:10 pm and recalls his wife being home thereby indicating that the sighting occurred sometime before 9:00 pm." Based on official mile-marker and speed limit data published in 2008, I estimate that they could have arrived at the point of the initial sighting by about 8:26 PM, by departing at about 5:30 PM, and exceeding the speed limit by 2 km. Departure at 5:48 PM plus 10 km/h over the speed limit would also work. The actual time of the sighting can never be known, but it could plausibly have occurred at the time of the re-entry, which is what I believe happened. In closing, I offer an ephemeris generator to enable researchers to evaluate the visibility of the decay from other locations in the region. Harro Zimmer's trajectory data is hard-wired into the spreadsheet. Simply enter the site's latitude, longitude and height above mean sea-level, and the topocentric coordinates of the trajectory will be re-calculated. Celestial coordinates are also included. http://satobs.org/seesat_ref/96069B/96069B_decay_ephemeris.xls Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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