Ed Cannon posted: >What hypotheses are offered to explain how >it can continue to flash at the same time each night? If I pick March 21, 2003 at 0400 UT, the sun is very nearly RA 0 Hr 0 Mn. If I take the elset for 20066 and generate a prediction for latitude 0, longitude 145.5 west, I get an altitude of very nearly 90 degrees (since this is the location of the sub-satellite point) and an RA of about 6 Hr 12 Mn. When the flashes are seen at 0400 UT, the solar panels are pointing half way between the sun and the observer. Since the difference in RA of 6 hours represents 90 degrees, it is clear that the angle of the solar panels relative to the long axis of the spacecraft is about 45 degrees. The solar panels are sending the reflected sunlight in a north-to-south (or south-to-north) path and the critical angle is the 90 degrees for the sun-satellite-observer angle, so it just does not make all that much difference whether the sun is at declination -20, 0, or +20. In this geometry, the sun-satellite-observer angle is changing because the satellite and the observer are turning at the daily rate of 1 degree every 4 minutes. So the reflections from the panels will "sweep" across the Earth from east to west at a rate of 1 degree per 4 minutes. One degree at a distance of 22000 miles is about 500 miles (in projection), so if there was something distinctive about these flashes (like the Superbird A phase change time), a time difference from east coast to west coast could be measured just like Superbird A. The flashes from one of the two DSPs that Rainer Kracht is tracking (20929 and 26356) should be visible from the US in the morning sky under a similar 90 degree angle. Object 20929 is above longitude 38 west. It crossed RA 6 Hrs about 20:50 UT. He reported flashes from 20:55 to 21:07 and from 21:18 to 21:27 UT on Feb 25. This DSP crosses 18 Hrs RA about 08:40 UT. So flashes should be visible from the US in the morning sky near that time. Object 26356 is above longitude 8 east. It is not visible from the US. It crossed RA 6 Hrs about 17:40 UT on March 21. Rainer saw fainter flashes about 18:16. It crossed RA 18 Hrs about 05:35 UT on March 21. Since this object is near the meridian for Europe, its 90 degree flashes are probably only visible in the wintertime. Possibly Greg Roberts could try for it now that it is fall in South Africa. Rainer reported that he observed bright flashes from this object at 22:50 for only two minutes. The RA at 22:50 on March 21 is about 11 Hrs 15 Mn. This gives a sun-satellite-earth angle of about 170 degrees and a half angle of about 85 degrees. This would imply some kind of panel pointing almost straight at the Earth. This would also imply that flashes could be seen at the RA of 12 Hrs 45 Mn, which would occur 90 minutes after the flashes he saw. It would also imply flashes from the other DSPs both 5 hours and 7 hours before/after their 90 degree flash times. Mike McCants USA 39 1 20066U 89046A 03080.72784648 0.00000000 00000-0 00000+0 0 00 2 20066 6.8620 52.8558 0060003 242.6560 0.0000 1.00273400 02 DSP 15 (USA65) 1 20929U 90095A 03056.00000000 .00000000 00000-0 00000-0 0 02 2 20929 6.8243 60.4532 0007040 337.3686 78.3868 1.00272831 08 DSP 20(USA149) 1 26356U 00024A 03071.38900906 0.00000000 00000-0 00000-0 0 07 2 26356 0.6979 317.6720 0004000 60.1177 299.8823 1.00262120 02 ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Wed Mar 26 2003 - 14:45:01 EST