RE: NROL-76 elements from observations

From : Ted Molczan via Seesat-l < : Ted Molczan via Seesat-l < seesat-l_at_satobs.org





The following elements are derived from observations by Leo Barhorst, Kevin Fetter, Sergey Guryanov and Scott Tilley: USA 276 390 X 409 km 1 42689U 17022A 17144.45083662 .00000000 00000-0 00000-0 0 05 2 42689 49.9984 162.7662 0014150 91.2112 269.0477 15.56119177 09 Arc 20170523.76-0524.47 WRMS resid 0.059 totl 0.021 xtrk Sergey described it as "brighter than 3 mag," which based on the circumstances of his observation, suggests a standard visual magnitude of about 4 (1000 km range, 90 deg phase angle). The ground track nearly repeats after 3 days and 46 revs. U.S. imagery intelligence satellites tend to employ orbits with ground tracks that repeat, or nearly so, after 2, 3 or 4 days. The orbital solution is still fairly preliminary, but it is interesting to note that the argument of perigee is near 90 deg. If this is confirmed by subsequent observations, and if it remains more or less constant long-term, then the orbit is of the frozen type. Frozen orbits are intended to maintain as nearly a constant altitude above geoid as possible around the entire orbit. The argument of perigee may be frozen near 90 deg or 270 deg. Below is a partial of list of satellites that have employed frozen orbits that I compiled in Jan 2007: GEOS-3 radar altimeter Seasat 1 SAR, radar altimeter GEOSAT radar altimeter Spot Earth resources imaging Lacrosse SAR UARS various Earth sensors JERS 1 SAR Topex/Poeidon radar altimeter ERS SAR, radar altimeter RadarSat SAR GEOSAT FO radar altimeter Landsat 7 Earth resources imaging Terra spectroradiometers, radiometer EO-1 Earth resources imaging Jason 1 radar altimeter Envisat SAR, radar altimeter, radiometers Aqua radiometers, microwave sounder Icesat altimeter, radiometer ALOS SAR, radiometer USA 193 classified The known sensors of the above payloads predominantly employed radio waves, but some were optical. A frozen orbit is strong evidence of an imaging payload, but not all imagers employ frozen orbits. To the above list, we can add the three Worldview optical imaging satellites built on the Ball Aerospace BCP-5000 bus. Ball Aerospace is believed to have built USA 276, the payload of NROL-76, which adds to our interest in the possibility that its orbit may be frozen. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l