AC-156 launch timeline
Posted: June 17, 2001

T-0:00:02.4 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+0:00:00 Launch
Liftoff The Atlas 2AS rocket, designated AC-156, lifts off and begins a vertical rise away from launch pad 36B at Cape Canaveral Air Force Station, Florida.
T+0:00:08 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+0:00:58.8 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+0:01:15.6 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. They had burned out at T+plus 55.6 seconds, but remained attached until the vehicle passes into preset safety zone.
T+0:01:56.3 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+0:02:43.1 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+0:02:46.3 Jettison Booster Package
Booster sep The bottom engine structure with the two booster engines is separated from the Atlas vehicle.
T+0:03:25.2 Jettison Payload Fairing
Fairing separation The 14-foot diameter aluminum payload fairing that protected the ICO satellite during launch is separated once heating levels drop to predetermined limits.
T+0:05:02.5 Sustainer Engine Cutoff
SECO SECO is commanded once minimum residual propellant is sensed inside the Atlas booster stage.
T+0:05:04.5 Atlas/Centaur Separation
Atlas separation The Atlas booster stage separates from the Centaur upper stage. Over the next few seconds, the Centaur engine nozzles are extended and liquid hydrogen and liquid oxygen systems are readied for engine ignition.
T+0:05:21.0 Centaur 1st Main Engine Start
MES-1 MES 1, the longer of the two Centaur firings begins to inject the upper stage and ICO spacecraft into a parking orbit with a perigee of 90.4 nautical miles and apogee of 5,455.2 nautical miles inclined 44.55 degrees.
T+0:10:45.7 Centaur Main Engine Cutoff
Coast MECO 1 occurs the Centaur engines are shutdown, arriving in a planned parking orbit. The vehicle begins a lengthy coast period to reach the high point of the orbit before the second Centaur burn.
T+1:49:14.6 Centaur 2nd Engine Start
MES-2 MES 2 occurs over the Southern Indian Ocean. The burn will propel the ICO satellite into the intended Medium Earth Orbit (MEO). The rocket's guidance computer will command the burn's conclusion once the proper orbit is achieved.
T+1:49:53.4 Centaur Main Engine Cutoff
MECO-2 At MECO 2, the Centaur/ICO vehicle should be in the required transfer orbit with a perigee of 5,458.5 nautical miles, apogee of 5,460.4 nautical miles, inclined 44.91 degrees. Moments later, the stage begins aligning to the satellite separation attitude.
T+1:52:43.4 Spacecraft Separation
Spacecraft separation The ICO F-2 global telephone and data relay satellite is released into orbit from the Centaur upper stage to complete the AC-156 launch.

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

Flight data file
Vehicle: Atlas 2AS (AC-156)
Payload: ICO F-2
Launch date: June 19, 2001
Launch window: 12:41-2:41 a.m. EDT (0441-0641 GMT)
Launch site: SLC-36B, Cape Canaveral, Fla.
Satellite broadcast: Telstar 5, Trans. 23, C-band

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

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

ICO - Description of the satellite to be launched on AC-156.

Launch windows - Listing of the available times to launch in coming days.

Restricted zone - Map outlining the Launch Hazard Area where mariners should remain clear for the liftoff.

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

Flight profile
Track the major launch events for the Atlas 2AS rocket carrying the ICO satellite on Spaceflight Now's interactive flight profile page (requires JavaScript).