PAN search elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Mon Sep 07 2009 - 12:40:49 UTC

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    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
    
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