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 search. 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 manually. 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: http://satobs.org/seesat/May-2010/0168.html 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 stars. 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 http://mailman.satobs.org/mailman/listinfo/seesat-l
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