Spaceflight Now: Atlas launch report

AC-157 launch timeline
Posted: December 4, 2000

Note: The animation images used below are NOT meant to depict the classified NRO payload being launched on this mission. Rather it is to illustrate a generic Atlas cargo.

T-00:02.4 Engine start
Engine start Atlas booster and sustainer engines are ignited and undergo checkout prior to liftoff. The two ground-start boosters will light a half-second before launch.
T+00:00 Launch
Liftoff The Atlas 2AS rocket, designated AC-157, lifts off and begins a vertical rise away from launch pad 36A at Cape Canaveral Air Force Station, Florida.
T+00:08 Roll Program
Roll During vertical ascent, Atlas begins a seven-second roll maneuver to align itself with proper flight azimuth. Following the roll, the Centaur inertial guidance system controls pitch and yaw programs.
T+00:58.5 Air-lit SRB Ignition
Air-lit The remaining two solid rocket boosters strapped to the Atlas are ignited once onboard computer software determines the two ground-start SRBs have burned out, about two seconds earlier.
T+01:08.9 Jettison Ground-Lit SRBs
Ground-lit sep The two spent solid rocket boosters that were ignited on the ground are jettisoned to fall into the Atlantic Ocean.
T+01:56.6 Jettison Air-Lit SRBs
Air-let sep Computer software will determine the air-start solid rocket boosters have burned all their propellant and should be jettisoned from the Atlas vehicle. The two SRBs will fall into the Atlantic Ocean.
T+02:44.9 Booster Engine Cutoff
BECO BECO occurs when axial acceleration of 5.0 g is obtained. Sustainer engine provides the continued boost toward orbit for the Atlas rocket.
T+02:47.91 Jettison Booster Package
Booster sep The bottom engine structure with the two booster engines is separated from the Atlas vehicle.
T+03:25.2 Jettison Payload Fairing
Fairing separation The 14-foot diameter aluminum payload fairing that protected the NRO satellite during launch is separated once heating levels drop to predetermined limits.
T+04:58.0 Sustainer Engine Cutoff
SECO SECO is commanded once minimum residual propellant is sensed inside the Atlas booster stage.
T+04:59.9 Atlas/Centaur Separation
Atlas separation The Atlas booster stage separates from the Centaur upper stage. Over the next few seconds, the Centaur liquid hydrogen and liquid oxygen systems are readied for engine ignition.
T+05:16.5 Centaur 1st Main Engine Start
MES-1 MES 1, the longer of the two Centaur firings begins to inject the upper stage and NRO spacecraft into a parking orbit with a perigee of 95 nautical miles and apogee of 466 nautical miles inclined 28.2 degrees.
T+09:54.2 Centaur Main Engine Cutoff
Coast MECO 1 occurs the Centaur engines are shutdown, arriving in a planned parking orbit. The vehicle begins a coast period over the mid-Atlantic before arriving at the required location in space for the second burn.
T+24:17.8 Centaur 2nd Engine Start
MES-2 MES 2 occurs over the Atlantic Ocean between the African Ivory Coast and Ascension Island before the rocket passes over the equator. The burn lasts until all the Centaur fuel is used, placing the NRO payload into a geosynchronous transfer orbit.
T+25:48.8 Centaur Main Engine Cutoff
MECO-2 At the point of MECO 2, the Centaur/NRO vehicle should be in the required transfer orbit with a perigee of 146 naut. miles, apogee of 20,247 naut. miles, inclined 26.5 deg. Moments later, the stage begins aligning to the satellite separation attitude.
T+29:35.8 Spacecraft Separation
Spacecraft separation The classified payload for the U.S. National Reconnaissance Office is released into orbit from the Centaur upper stage to complete the AC-157 launch.

Image and data source: International Launch Services and Lockheed Martin Astronautics.

Flight data file
Vehicle: Atlas 2AS (AC-157)
Payload: Classified NRO
Launch date: Dec. 5, 2000
Launch window: 8:14-10:12 p.m. EST (0114-0312 GMT on 6th)
Launch site: SLC-36A, Cape Canaveral, Fla.

Pre-launch briefing
Atlas 2AS vehicle data - Overview of the rocket that will launch the classified NRO payload.

Ground track - See the trajectory the rocket will follow during its flight.

Atlas index - A directory of our previous Atlas launch coverage.