NROL-36 search elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Wed Aug 01 2012 - 15:28:37 UTC

  • Next message: alberto rango: "4641 SATOBS 31 JUL 2012."

    NROL-36 is scheduled for launch on an Atlas V-401, from VAFB, on 2012 Aug 02 at 07:40 UTC.
    
    http://www.spaceflightnow.com/atlas/av033/status.html
    
    The target orbit appears to be NOSS (Naval Ocean Surveillance System). If it is a NOSS, and if the launch window is
    planar (it usually is), then in the event of a delay, the launch window will move 14 min earlier per day of delay.
    
    If it is another 3rd generation NOSS launch, then the primary payload would consist of two satellites that would orbit
    in close formation.
    
    Here are approximate initial elements:
    
    NOSS                                                   1015 X 1206 km
    1 79601U          12215.40011574  .00000000  00000-0  00000-0 0    09
    2 79601  63.4386 149.6018 0127783 180.8421 355.8429 13.39314612    05
    
    The RAAN probably is accurate to within 1 deg. I am less confident of the mean anomaly, so prediction time errors of at
    least several minutes are possible.
    
    Secondary payloads consist of 11 cubesats, to be deployed more than three hours after launch, after at least a couple of
    orbit manoeuvres by the Centaur. Preliminary TLEs appear at the bottom of the following page:
    
    http://cubesat.org/index.php
    
    For example:
    
    Deploy1-SMDC1.2                                          489 X 765 km
    1 99991U 00000    12215.44833333 0.00000000  00000-0  00000-0 0  0002
    2 99991  66.2600 135.6350 0197000 306.4500 124.9559 14.80308034000003
    
    The following sequence of manoeuvres explains all but the large change in RAAN:
    
    1. MET 01h56m10s  manoeuvre at perigee to 66.26 deg, 494 X 1014 km orbit. Line of apsides effectively rotates 180 deg.
    
    2. MET 02h41m34s  manoeuvre to reduce apogee to 765 km and rotate line of apsides -54.4 deg.
    
    The orbit at the end of the second manoeuvre would be:
    
    Centaur pre-Cubesat deployment                           489 X 765 km
    1 79602U          12215.43164353  .00000000  00000-0  00000-0 0    07
    2 79602  66.2600 149.3144 0197000 306.4500  30.6500 14.80308034    02
    
    Propagating to the epoch of the 99991 TLE (at MET 03:05:36) reveals a very similar result, except for the RAAN:
    
    1 79602U          12215.44833333  .00000000  00000-0  00000-0 0    09
    2 79602  66.2600 149.2662 0197000 306.4386 119.5918 14.80308034    08
    
    The along-track time difference is less than 2 min.
    
    The ~14 deg difference in RAAN is troubling. An older set of preliminary orbits revealed little or no change in RAAN. I
    have not attempted to explain the difference, nor to determine the feasibility of the RAAN change.
    
    I found no evidence of a re-entry zone in the NOTAMs; therefore, it appears that the Centaur will not be de-orbited
    immediately at the end of its mission. The 99991 and 79602 TLEs are reasonable starting points to search for it;
    however, I would not be surprised if it further lowers its perigee and makes a plane change after it deploys the
    cubesats. This and any fuel dump would occur in eclipse, over the Pacific Ocean.
    
    The NROL-36 objects will be well placed for visual observation in the evening from mid-northern latitude locations.
    
    Happy hunting!
    Ted Molczan
    
    
    _______________________________________________
    Seesat-l mailing list
    http://mailman.satobs.org/mailman/listinfo/seesat-l
    



    This archive was generated by hypermail 2b29 : Wed Aug 01 2012 - 15:29:39 UTC