PAN is a Lockheed Martin-built communications satellite, belonging to an undisclosed agency of the U.S. Government. It is scheduled for launch on 2009 Sep 08, between 21:35 UTC and 23:44 UTC, from Cape Canaveral, aboard an Atlas V-401. Its planned orbit is GEO (geosynchronous), and I believe that its launch trajectory will be of the Extended Coast type, which typically results in a highly elliptical parking orbit, in which the vehicle coasts for a period of up to two hours, before manoeuvring to GTO (geosynchronous transfer orbit). The resulting orbit is lower in eccentricity and inclination than that of the more common GTO, in which the manoeuvre to GTO occurs at the first descending node. This reduces the delta-V required of the payload to enter GEO, which saves fuel, and extends its maximum useful life. I have neither the tools nor the knowledge to design the orbits of an Extended Coast launch; even if I did, there is insufficient public information to constrain the analysis to accurately predict the orbits of PAN. So, I looked for a suitable proxy among past GEO launches, and found that Astra 1KR (06012A / 29055) had Centaur burn times roughly similar to those of PAN. Astra 1KR entered a 24.83 deg, 167 km x 22442 km parking orbit, and a 23.97 deg, 6212 x 35787 km GTO; over the subsequent two weeks, it performed a series of manoeuvres to enter an initial GEO orbit. After performing some surgery (more like mayhem) on the Astra 1KR orbits, I obtained the following rough PAN search elements. Assuming launch on Sep 08 at 21:35 UTC, this is the approximate parking orbit, valid until after the GTO manoeuvre, approximately 23:32 UTC: Parking orbit 167 X 22442 km 1 75000U 09251.98027778 .00000000 00000-0 00000-0 0 00 2 75000 24.8300 138.2905 6298500 144.0405 91.6200 3.69339000 08 The approximate transfer orbit is valid until at least first apogee. Transfer orbit 7068 X 35786 km 1 75000U 09251.98027779 .00000000 00000-0 00000-0 0 01 2 75000 23.7000 146.7000 5164154 180.2405 46.6000 1.87265000 05 It is highly probable that the actual orbits will differ significantly from the above, especially the GTO, which could have a much lower inclination. So, I doubt that these will be adequate to support visual observation, except possibly to see the Centaur fuel dump, which has the appearance of a bright comet, readily visible to the unaided eye over a period of a few tens of minutes. The fuel dump typically begins about 30 to 40 min after payload separation. Payload separation is expected at about T+01:59:25, so assuming launch on Sep 08 at 21:35 UTC, look for the fuel dump in the vicinity of the transfer orbit, beginning about 00:00 UTC on Sep 09. Once in GEO, PAN should be readily observable. Lockheed has disclosed that it is built on its A2100 bus, and based upon the model of launch vehicle and the transfer orbit, I believe it to be the A2100AX variant. Greg Roberts and Scott Campbell have reported 25 brightness observations of four GEO satellites based on the A2100AX, which was typically mag 10 +/- 1 mag, as seen from their vantage points, within about 30 deg of the equator. Standard visual magnitude is 2.9 (1000 km, 90 deg phase angle). Coefficient of phase is about 0.01 mag/deg. A review of the launch history of several A2100AX GEO missions, reveals that they typically take 2 to 3 weeks to complete a series of manoeuvres to reach their initial geosynchronous orbit. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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