NROL-52 was launched from CCAFS on an Atlas V-421 on 2017 October 15 at 07:28 UTC. I believe that its payload is the second of a new generation of SDS (aka Quasar) communication relay. It is likely to be catalogued as USA 279 (2017-066A). 1. Observations We had excellent tracking of the initial orbit, thanks to Paul Camilleri, who is ideally placed to observe many of the types of launches that interest us. He observed and imaged the payload on 2017 October 15, between 11:34 UTC and 12:57 UTC, and the Centaur from 11:28 UTC to 14:56 UTC. His observations are here: http://satobs.org/seesat/Oct-2017/0065.html I found the time of the final two Centaur points to be one hour late, perhaps due to a typo. Subtracting 1 h yielded good residuals within the differential correction. 2. Payload orbital elements in GTO The residuals between the observations and estimated pre-launch elements were about 0.01 deg cross-track, and about 10 s to 20 s in time. The object appeared to be falling very gradually behind prediction in time, which suggested a bit higher orbit than estimated. For the orbital analysis, I propagated the pre-launch estimated TLE to the start of the observations. I differentially corrected it in two different ways. For the following TLE, I adjusted only the mean-anomaly: USA 279 1113 X 35802 km 1 76402U 17066A 17288.48263889 .00000000 00000-0 00000-0 0 06 2 76402 18.6773 325.4984 6983839 178.5905 121.9313 2.21873127 02 Arc 20171015.48-1015.54 WRMS resid 0.022 totl 0.011 xtrk To account for the possibly higher orbit, I adjusted only the mean motion to produce the following TLE: USA 279 1134 X 35924 km 1 76402U 17066A 17288.48263889 .00000000 00000-0 00000-0 0 06 2 76402 18.6773 325.4987 6983832 178.5899 122.0404 2.20915106 06 Arc 20171015.48-1015.54 WRMS resid 0.006 totl 0.004 xtrk The above TLEs should bracket the actual position until the object manoeuvres. 3. Centaur de-orbit The Centaur's MES3 burn at approximately 08:33 UTC (MET 01:05) put it on a trajectory to de-orbit about 750 km south of Hawaii. I obtained the following orbital elements from Paul's observations: Centaur -244 X 28046 km 1 76403U 17066B 17288.47777778 .00000000 00000-0 00000-0 0 03 2 76403 18.8913 323.6165 6975099 166.6469 161.4027 3.00742648 06 Arc 20171015.48-1015.62 WRMS resid 0.005 totl 0.002 xtrk I used GMAT 2017a (General Mission Analysis Tool) to propagate the above TLE to re-entry. A kmz file containing the final portion of the resulting trajectory is here: http://satobs.org/seesat_ref/NROL-52/NROL-52_Centaur_re-entry.kmz The following graphic was generated using the kmz file: http://satobs.org/seesat_ref/NROL-52/NROL-52_Centaur_deorbit.jpg The white rectangle is the NOTAM hazard zone. Hawaii is just visible on the horizon, 750 km to the north. The re-entry impact zone was an approximately 160 x 600 km rectangular region, centred near 11.87 N, 154.63 W. The depicted re-entry trajectory begins at about 1000 km altitude. The alternating red and white line segments span 5 s of flight. The TLE propagated to theoretical impact within the NOTAM boundaries, near 11.92 N, 155.62 W, at about 15:57 UTC - 12 min. after the start of the NOTAM period. The Centaur reached a maximum velocity of nearly 10.2 km/s inertial (not far below escape velocity), 9.7 km/s relative the atmosphere. Maximum deceleration of about 44 G occurred at about 49 km altitude. Nearly all horizontal velocity had been lost by 30 km altitude, following which any surviving debris would have fallen almost vertically. The final vertical descent is clearly depicted in the above graphic. The GMAT scripts used to propagate the TLE, and the Excel ephemeris spreadsheet used to analyze the results and produce the kml file, are here: http://satobs.org/seesat_ref/NROL-52/NROL-52_Centaur_re-entry_analysis.zip Both scripts begin with a state vector generated by the TLE. Version #1 covers the complete descent; #1a covers only the portion down to about 88 km altitude, but at higher time resolution. I combined the output of both and extracted data at approximately 5 s intervals. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Sun Oct 15 2017 - 17:48:32 UTC
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