NROL-35 pre-launch elements

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Wed, 10 Dec 2014 22:38:44 -0500
NROL-35 is scheduled for launch on 2014 Dec 12 at 03:17 UTC, from Vandenberg AFB, aboard an Atlas V-541.

http://spaceflightnow.com/2014/12/10/nrol35-mission-status-center/

The payload probably is the next HEO SIGINT, hosting SBIRS-HEO 3. NROL-42, expected to launch in a couple of years from
VAFB on the same model of rocket, appears to be the same type of mission.

The last launch in the series was NROL-28 in March 2008, from VAFB on an Atlas V-411. Its payload is known as USA 200
(08010A / 32706).

The Atlas V-541 has roughly 40 percent greater performance than the Atlas V-411, which suggests that NROL-35 will carry
a significantly heavier payload. Some of the extra performance will be used to de-orbit the Centaur stage on its first
revolution, to impact in the Indian Ocean south of Australia.

Assuming launch at the above time, and a mission identical to NROL-28, these would be the approximate initial orbits of
payload and Centaur:

Payload                                               1117 X 37562 km
1 72001U          14346.16099538  .00000000  00000-0  00000-0 0    02
2 72001  63.5608 209.8837 7085471 271.7444 359.8457  2.10489866    03

Centaur CCAM                                          1087 X 37455 km
1 73001U          14346.18182871  .00000000  00000-0  00000-0 0    08
2 73001  64.6290 210.6009 7089441 271.7256  15.5928  2.11333612    03

The payload's elements are derived from one of the TLEs we produced from optical tracking of NROL-28, about a week
after launch, prior to its first manoeuvre:

1 32706U 08010A   08081.53973202  .00000000  00000-0  00000-0 0    08
2 32706  63.5657  40.6363 7087561 271.7437  15.6600  2.10485232    04

No two missions of this type are likely to have identical initial elements, and given the use of a much different
launch vehicle, the actual elements of NROL-35 almost certainly will differ somewhat.

The Centaur 73001 TLE derives from backward propagation of recent elements of 08010B / 32707. It reflects the typical
CCAM (Collision and Contamination Avoidance Maneuver). Since NROL-35's Centaur is to be de-orbited, its final elements
will be different.

If the de-orbit manoeuvre occurs at the epoch of the 73001 TLE, then the various constraints could be satisfied by
changing the eccentricity, argument of perigee, mean anomaly, and mean motion as follows:

Centaur de-orbit                                      -173 X 33549 km
1 73002U          14346.18182873  .00000000  00000-0  00000-0 0    01
2 73002  64.6290 210.6009 7310000 258.7256  18.7000  2.47800000    02

This orbit would impact in the NOTAM zone about 27 min. into the impact window. Delta-V would be about 650 m/s, which
does not seem outrageous.

Delaying the burn nearly an hour to exactly T+02:00 h, and following the same procedure yields this result:

Centaur de-orbit                                      -274 X 33588 km
1 73003U          14346.22013889  .00000000  00000-0  00000-0 0    07
2 73003  64.6290 210.5958 7350000 263.6000  51.7500  2.48300000    09

This orbit would also impact in the NOTAM zone about 27 min. into the impact window, but delta-V would be reduced to
about 270 m/s.

The above estimates seem reasonable, but NRO launches have the potential for surprise, especially when there is a
change of rocket and/or payload. If you have other ideas about the initial orbits and/or payload, please post your
analysis.

Ted Molczan



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Received on Wed Dec 10 2014 - 21:39:19 UTC

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