X-37B OTV-1 Found in Orbit

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Sun May 23 2010 - 02:49:01 UTC

  • Next message: Kevin Fetter: "Re: X-37B OTV-1 Found in Orbit"

    On 2010 May 20 UTC, Kevin Fetter and Greg Roberts independently observed an
    object in orbit, which I have identified as X-37B OTV-1 (2010-015A / 36514).
    It was in a 40 degree, 401 X 422 km orbit, with the following elements:
    1 36514U 10015A   10141.34117384  .00001134  00000-0  17740-4 0    09
    2 36514  39.9923 182.0995 0015696 192.8143 167.2271 15.52662300    01
    Initial observations indicate a standard visual magnitude of about 5 (1000
    km, 90 deg phase angle). It should reach magnitude 2.5 on well-illuminated,
    high elevation passes.
    The ground track repeats almost exactly after 61 revs, which takes about 4
    days. Ground tracks that repeat at 2, 3 or 4 day intervals have been a
    common feature of U.S. imaging reconnaissance satellites, so this finding
    could be a clue as to the mission. As a wild guess, another possibility may
    be to create a fixed set of re-entry ground tracks, that repeat fairly
    frequently, set up to simplify the eventual return to Earth.
    The following is a summary of the search.
    Typically, we find satellites in secret orbits in one of two ways:
    deliberate searching or chance sighting. This case is a first for us, in
    that Kevin caught it by chance on video while looking for something else,
    and Greg caught it eight hours later, after conducting numerous planar
    searches during the month since OTV-1's launch on Apr 22 UTC.
    Pre-launch, I had guessed that the inclination likely would be between 28.5
    deg and 40 deg. The launch azimuth, estimated from NOTAM data, indicated an
    approximately 33.5 deg orbit, so I posted several search elements covering
    33.5 deg orbits of various altitude, which became the initial focus of the
    An early probable sighting was made by a North American colleague, early on
    Apr 24 UTC. The observation was made under extremely poor sky conditions,
    which made it difficult to identify all of the stars that the object passed.
    At least one accurate time and position was believed to have been obtained.
    Unfortunately, no other observer was in a position to quickly attempt a
    confirming observation, so the trail went cold.
    Greg used his automated camera pointing system to conduct planar searches of
    the 33.5 deg search plane. Essentially, this involves staring at a point on
    the search orbit for a period not less then one revolution of the satellite
    about the Earth. If the satellite is there, and sufficiently bright, it will
    be seen. It is simple in principle, but difficult and tedious to do
    Greg's automated system is ideal for planar searching, and he made a
    considerable effort to optimize it for OTV-1, to the extent of mounting two
    cameras pointing at different elevations, to cover the widest possible swath
    of sky, essential because of the considerable uncertainty in the orbit. He
    had to carefully balance trade offs in field of view and sensitivity.
    Greg battled the usual problems with weather, which interrupted or aborted
    several searches. He also experienced unusual hardware problems, which he
    solved with his usual ingenuity. Despite these challenges, Greg eventually
    completed several thorough searches, but did not see OTV-1. In the meantime,
    I had become aware of rumours that the inclination was 40 deg. There was no
    way to determine their veracity, or even their origin, but since Greg had
    shown that it most likely was not at 33.5 deg, and 40 deg was within our
    pre-launch guesstimate, it seemed reasonable to shift the search there.
    Normally, a Cape Canaveral launch targeting a 40 deg inclination, would have
    headed toward the north east, but this launch was east south-east. However,
    the Atlas 5-401 launch vehicle was known to have significantly greater
    performance than required by the mass of OTV-1; therefore, it seemed
    feasible for it to have started out on a heading that would result in a 33.5
    deg inclination, and then to have yaw-steered into a 40 deg orbit later in
    its ascent. GPS satellite launches on Delta 2 rockets commonly reach 37 deg
    initial orbits, following launch azimuths not very different from OTV-1's.
    On May 18, I produced several 40 deg inclination search elements, and Greg
    resumed his search on May 19, which was hampered by close proximity to the
    moon, and turned up nothing of interest.
    On May 20, Kevin Fetter posted a link to his video of a bright unknown
    satellite, obtained that day at 07:52:28 UTC:
    Knowing our history of fortuitous sightings, I quickly checked and confirmed
    that the object was not among those in known orbits, then checked the time
    and sky coordinates against our search orbits. It was sufficiently close to
    the new 40 deg search plane to be highly interesting, so I set about
    reducing the video imagery into time and sky-coordinates and evaluating
    possible orbits. After several hours analysis, I became convinced that Kevin
    probably had captured OTV-1, and that it was in approximately a 39 to 41 deg
    orbit, with 40 deg fairly likely. The uncertainty in inclination was due to
    the difficulty extracting accurate data from the video, which was obtained
    in poor sky conditions, and revealed only a few, widely spaced reference
    The results of Kevin's video came too late to assist Greg, who was busy
    performing his second planar search of the new 40 deg search orbit. At 18:51
    UTC, I received his report that at 16:31 UTC he had recorded an object of
    about the expected brightness, and direction and speed of travel relative
    the stars.
    I quickly determined that Kevin and Greg had independently observed the same
    satellite, in approximately a 410 km orbit, inclined at 40 degrees to the
    equator, in an orbital plane consistent with the circumstances of the launch
    of OTV-1. I was also able to confirm that our North American colleague had
    indeed seen OTV-1 back on April 24.
    Subsequent tracking and analysis on May 21 enabled the elements to be
    refined, as shown above, and confirmed that OTV-1 had been found.
    Ted Molczan
    Seesat-l mailing list

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