AC-203 launch timeline
Posted: December 11, 2003

T-00:02.7 Engine Start
The Russian-built RD-180 engine rumbles to life and builds to 74 percent thrust. A health check of eight engine parameters is performed by the rocket's onboard computer a half-second before liftoff.
T+00:00 Liftoff
The fourth flight for Atlas 3 begins as the rocket is released from pad 36B at Cape Canaveral Air Force Station, Florida.
T+00:02 Roll and Pitch Programs
During the vertical ascent Atlas completes a 7-second roll maneuver to align itself with proper flight azimuth. Following the roll, the rocket begins a pitch-over maneuver with Centaur inertial guidance system in control of pitch and yaw programs.
T+00:06 Throttle Up
The RD-180 engine is throttled up from its liftoff thrust of 74 percent to over 90 percent after the rocket clears the launch pad 36B tower.
T+00:35 Throttle Down
The RD-180 engine is throttled down to a thrust level of about 65 percent to ease the rocket through the dense lower atmosphere.
T+01:05 Through Max-Q
The rocket passes through maximum dynamic pressure and goes transonic. The RD-180 now throttles back up to its cruise setting of about 87 percent thrust, ramping up to 5 g's. The engine will gradually throttle back down to maintain a constant vehicle acceleration.
T+02:55 Throttle Down
To prepare for the upcoming engine shutdown, the RD-180 is throttled down to 47 percent.
T+03:01 Booster Engine Cutoff
The RD-180 engine is commanded to cut off once minimum residual propellant is sensed inside the Atlas booster stage.
T+03:07 Atlas/Centaur Separation
Six seconds after engine shutdown, the Atlas booster stage separates from the Centaur upper stage. Over the next several seconds, the Centaur liquid hydrogen and liquid oxygen systems are readied for engine ignition and the nozzle extension is deployed.
T+03:18 Centaur 1st Main Engine Start
MES 1, the longer of the two Centaur firings, begins to inject the upper stage and UHF F11 communications satellite into a low altitude parking orbit around Earth.
T+03:26 Jettison Payload Fairing
The 14-foot diameter aluminum payload fairing that protected the UHF F11 satellite during launch is separated once heating levels drop to predetermined limits.
T+14:54 Centaur Main Engine Cutoff
MECO 1 occurs when the single Centaur engine is shut down, with the rocket 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+24:37 Centaur Main Engine Re-start
MES 2 occurs over the Atlantic Ocean between the African Ivory Coast and Ascension Island before the rocket passes just north of the equator. The burn accelerates the vehicle and satellite into the required geosynchronous transfer orbit.
T+27:42 Centaur Main Engine Cutoff
At the point of MECO 2, the Centaur and UHF F11 stack should be in the required transfer orbit, completing the powered phase of the launch. The stage then begins aligning to the satellite separation attitude.
T+32:28 Spacecraft Separation
The U.S. Navy's UHF F11 communications satellite is released into space from the Centaur upper stage to complete the AC-203 launch.

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