X-37B OTV-1 - circumstances of orbit-raising of Aug 09

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Wed Aug 25 2010 - 04:09:21 UTC

  • Next message: Derek C Breit: "RE: X-37B OTV-1 - circumstances of orbit-raising of Aug 09"

    Leonard David has nicely documented X-37B OTV-1's orbit-raising of Aug 9, including the involvement
    of several SeeSat-L members in the subsequent tracking and orbit analysis:
    One of the findings reported in the article is the apparent timing of the two orbit-raising
    manoeuvres to enable nearly continuous monitoring by several Air Force Satellite Control Network
    (AFSCN) tracking stations. Since that fact may be useful in understanding future manoeuvres, I want
    to provide some technical details that are not appropriate for a news article, but well-suited to
    this forum.
    Propagating the new orbit backward to the time of its closest separation from the original orbit,
    revealed the mid-point between the manoeuvres, which were performed on opposite sides of the Earth,
    near a perigee and an apogee. 
    The first manoeuvre occurred on Aug 09, about 17:12 UTC, near 40 S, 98 E. The spacecraft was near
    the apogee of its original 403 X 420 km orbit, and manoeuvred to raise its perigee by 42 km,
    resulting in a 420 X 445 km orbit. Since the new perigee was greater than the original apogee, the
    line of apsides was effectively rotated 180 deg. 
    About 16 minutes later, the spacecraft came within range of the Air Force Satellite Control Network
    (AFSCN) tracking station at Hawaii, the first of five AFSCN stations in a position to monitor it
    throughout the remainder of the manoeuvre sequence. 
    The final manoeuvre occurred half an orbit after the first one, near the new apogee, at about 17:58
    UTC, near 40 N, 100 W. The perigee was raised 12 km, resulting in a 432 x 445 km orbit. This was
    just before LOS by the AFSCN station at VAFB, and well above the horizon of the Colorado AFSCN
    station. Depending on the duration of the burn, the New Hampshire station may also have been able to
    monitor it directly; it certainly would have been able to monitor the results.
    Below are the estimated AOS/LOS times of the AFSCN tracking stations that OTV-1 passed during the
    manoeuvre sequence:
       AOS        LOS
    17:38:28 - 17:48:29  AFSCN Hawaii Tracking Station, Kaena Point, Oahu, Hawaii
    17:40:14 - 17:49:36  AFSCN Guam Tracking Station, Andersen AFB, Guam
    17:47:42 - 17:58:13  AFSCN Vandenberg Tracking Station, Vandenberg AFB, California
    17:51:24 - 18:01:56  AFSCN Colorado Tracking Station, Schriever AFB, Colorado
    17:58:15 - 18:08:31  AFSCN New Hampshire Tracking Station, New Boston Air Station, New Hampshire
    AOS and LOS correspond to estimated time of rise/set, 2 deg above the horizon; actual AOS/LOS depend
    on local terrain, not considered in this analysis.
    Below are elsets documenting the manoeuvre. The pre-manoeuvre elset is derived from our last
    observations of the original orbit, on July 29. The two manoeuvre elsets are accurate estimates;
    their epochs correspond to the manoeuvre times.
    Pre-manoeuvre orbit                                      403 X 420 km
    1 36514U 10015A   10210.09309780  .00000000  00000-0  00000-0 0    09
    2 36514  39.9851 119.3456 0012533 356.3806   3.6913 15.52766118    04
    First manoeuvre                                          420 X 445 km
    1 36514U 10015A   10221.71696759  .00000000  00000-0  00000-0 0    05
    2 36514  39.9851  47.8421 0018773 266.6117   0.6500 15.45484000    09
    Final manoeuvre                                          432 X 445 km
    1 36514U 10015A   10221.74841435  .00000000  00000-0  00000-0 0    01
    2 36514  39.9851  47.6508 0009598 266.8531 175.6000 15.43360000    09
    Ted Molczan
    Seesat-l mailing list

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