The launch of NROL-76 from Cape Canaveral on a Falcon 9 v1.2 is scheduled for a two hour window that opens on 2017 Apr 30 at 11:00 UTC. As I write, the launch time is 11:15 UTC. https://spaceflightnow.com/2017/04/29/nrol-76-mission-status-center/ Below are links to analyses of the implications of the NOTAM zones for the orbit, by Cees Bassa and Marco Langbroek, respectively: http://satobs.org/seesat/Apr-2017/0199.html https://sattrackcam.blogspot.ca/2017/04/what-is-nrol-76-and-what-orbit-wil-it.html For now, I lean toward a LEO mission. I offer a couple of notional orbits, based on launch at 11:15 UTC: Below are the elements of a 50 deg, 300 km orbit. Payload 300 X 306 km 1 74200U 17120.47291669 .00000000 00000-0 00000-0 0 01 2 74200 50.0000 282.7603 0005000 90.0000 307.5000 15.90000000 02 I do not know the payload. There has been speculation that it could be an X-37B. That would be well within the performance capability of the launch vehicle, and I believe that it's wing span would just fit within the payload fairing of NROL-76, which is 5.2 m in diameter, and 13.9 m long. It can accommodate payloads up to 4.6 m in diameter. My earlier speculation included the possibility of a re-flight of the payload of NROL-21, USA 193, which failed shortly after it reached orbit in December 2006. It was launched on a Delta 7920-10C, which could launch about 3,700 kg into the orbit of USA 193. I have seen an estimate of its mass of about 2,300 kg. Below are elements for a USA 193 replacement mission. USA 193 replacement 353 X 366 km 1 74301U 17120.60307874 .00000000 00000-0 00000-0 0 04 2 74301 58.5000 289.6103 0010000 90.2000 319.8000 15.69650000 09 Stage 2 after de-orbit burn 59 X 365 km 1 74302U 17120.60307875 .00000000 00000-0 00000-0 0 06 2 74302 49.5000 274.2193 0232000 258.5002 159.5706 16.23000000 08 The epoch is for the time of the stage 2 de-orbit manoeuvre, which includes a plane change to align with the de-orbit zone. The delta-V would be about 2.045 km/s, mainly due to the plane change, which I believe would be feasible because of the large performance margin of the launch vehicle, per the following estimate: http://www.silverbirdastronautics.com/LVperform.html Launch Vehicle: Falcon 9 v1.2 (land recovery) w/standard fairing Launch Site: Cape Canaveral / KSC Destination Orbit: 353 x 366 km, 58.5 deg Estimated Payload: 10927 kg 95% Confidence Interval: 9515 - 12495 kg Note: Caution: limited technical data available Note: Possible dogleg ascent - performance impact estimated I have not completely discarded the possibility of a MEO or Molniya mission, but so far, a LEO mission seems to better fit the data. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Sun Apr 30 2017 - 05:08:33 UTC
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