RE: NROL-38 pre-launch elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Sun Jun 17 2012 - 17:37:49 UTC

  • Next message: Marco Langbroek: "NROL-38 potsponed"

    I have estimated a GTO that would enable the Centaur to be de-orbited near the time and mid-point of the NOTAM zone. The
    following TLEs are based on the launch that had been scheduled for 2012 June 18 between 12:26 and 13:25 UTC, assuming
    launch at window-open.
    
    I used the same parking orbit as in my earlier estimate:
    
    Parking orbit                                            259 X 272 km
    1 79301U          12170.53553244  .00000000  00000-0  00000-0 0    05
    2 79301  27.2800 271.6402 0010000 183.0000 359.3500 16.05000000    03
    
    By trial and error, I found that the following GTO would pass close to the mid-point of the re-entry zone, about 8 min
    later than the earliest time of the NOTAM (21:14 UTC):
    
    Descending-node GTO                                    269 X 29816 km
    1 79301U          12170.53553248  .00000000  00000-0  00000-0 0    09
    2 79301  21.2000 271.6349 6896886 182.7760 359.6507  2.77000000    02
    
    The TLE assumes an instantaneous manoeuvre at the first descending node (12:51 UTC, MET 00:25:10). If monitoring by
    Diego Garcia is required, then spacecraft separation would occur no earlier than about 13:03 UTC (MET 00:37:00).
    
    To a first approximation, compared with a conventional GTO (25.5 deg, 269 x 35786 km), the above GTO would add about 53
    m/s delta-V to the Centaur's GTO burn and 41 m/s to the spacecraft's manoeuvres to reach a 5 deg, GEO orbit - about 2.3
    percent of the total delta-V from LEO to GEO. My simplified estimates could have omitted some optimizations that would
    reduce this penalty.
    
    Propagating the orbit to the apogee (17:11:30 UTC, MET 04:45:30), and reducing the perigee as follows, results in impact
    in the centre of the re-entry zone at about 21:14 UTC:
    
    Centaur de-orbit                                      -826 X 29816 km
    1 79301U          12170.71631945  .00000000  00000-0  00000-0 0    00
    2 79301  21.1994 271.5464 7340000 182.9346 179.9308  2.88000000    09
    
    The delta-V would be 137 m/s; propellant use roughly 84 kg.
    
    In estimating the above orbits, I made no effort to account for the effects of the CCAM (collision and contamination
    avoidance manoeuvre) that occurs shortly after spacecraft separation.
    
    I made no effort to find an optimal solution, nor did I attempt to find the range of possible combinations of GTO and
    de-orbit delta-V, of which there are likely to be many.
    
    The prompt de-orbiting of EELV second stages seems to have become USAF/NRO/ULA standard operating procedure for LEO
    missions. To my knowledge, NROL-38 would be the first application to a GEO mission. It demonstrates a strong commitment
    to reducing the growth of debris in orbit, and seems a good use of the surplus performance of the EELVs relative typical
    mission requirements.
    
    I believe the following list is complete; final column lists the place of disposal.
    
    Nov 2006  DMSP F17       LEO  VAFB   Delta IV-Medium  Pacific Ocean
    Oct 2009  DMSP F18       LEO  VAFB   Atlas V-401      Solar orbit
    Apr 2010  X-37B OTV 1-1  LEO  CCAFS  Atlas V-501      Solar orbit
    Sep 2010  FIA Radar 1    LEO  VAFB   Atlas V-501      Indian Ocean
    Jan 2011  USA 224        LEO  VAFB   Delta IV-Heavy   Pacific Ocean
    Mar 2011  X-37B OTV 2-1  LEO  CCAFS  Atlas V-501      Indian Ocean
    Apr 2011  NOSS 3-5       LEO  VAFB   Atlas V-411      Pacific Ocean
    Mar 2012  FIA Radar 2    LEO  VAFB   Delta IV-Medium  Indian Ocean
    Jun 2012  NROL-38        GEO  CCAFS  Atlas V-401      Pacific Ocean (planned)
    
    The following paper reports in detail on the de-orbiting of DMSP F17's Delta IV 2nd stage:
    
    http://aiaa.kavi.com/apps/group_public/download.php/3138/Control%20Deorbit%20of%20Delta%20IV.pdf
    
    As for the payload of NROL-38, I am a bit less certain it is an SDS, but I have no better guess. We will have to wait
    and see where it goes and what it does. The launch has been delayed to 2012 Jun 20. I intend to revise the above TLEs
    accordingly, a little closer to launch.
    
    Ted Molczan
    
    
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