The Atlas 2AS is equipped with four strap-on solid rocket motors and is capable to lifting payloads of 3,719 kg (8,200 lb) into a geostationary transfer orbit.
The Atlas 2AS is a two-and-one-half stage launch vehicle. The Centaur upper stage is mounted on top of the one-and-one-half stage Atlas booster.
Solid Rocket Boosters
The SRBs are mounted around the aft portion of the Atlas (one in each quadrant) parallel to the vehicle's longitudinal axis with effective nozzle cant angles of 7 degrees and 11 degrees. Attachment to Atlas is accomplished by the Attach, Disconnect, and Jettison (ADJ) system consisting of an Inconel thrust pin and three pyrotechnically actuated thrusters. The SRBs are ignited sequentially in pairs beginning with the ground-lit (GL) pair ignition shortly before liftoff. The GL pair burns until propellant depletion, at which time a short delay is imposed and the air-lit (AL) pair is ignited. Each SRB provides an average sea-level thrust of 100,049 lbf and has a nominal web burn time of 52.15 seconds. The total SRB phase of flight lasts approximately 2 minutes.
Atlas booster propulsion is provided by the Rocketdyne MA-5A engine system, which includes the sustainer engine and booster engine system. All engines are ignited before liftoff and develop a total sea-level-rated thrust of 490,000 pounds. The section containing the booster engine is jettisoned (booster package jettison [BPJ]) at an axial acceleration of 5.0 g. Flight continues powered by the sustainer engine ("sustainer phase" flight) until propellant depletion.
The Atlas is connected to the Centaur by the interstage adapter. This aluminum structure provides the structural link between Atlas and Centaur. The Atlas is separated from the Centaur by a flexible linear-shaped charge system attached to the forward ring of the interstage adapter.
Centaur Upper Stage
Centaur avionics packages, mounted on the equipment module, control and monitor all vehicle functions. Centaur avionics perform the inertial guidance and attitude control computations for both Atlas and Centaur phases of flight, and control Centaur tank pressures and propellant use.
The Centaur propulsion system uses two RL10A-4-1 engines with extendible nozzles manufactured by Pratt & Whitney. Each engine is has a rated thrust of 22,256 pounds. The Centaur engines are restartable and are capable of multiple firings in space, separated by coast phases.
The stub adapter and equipment module are attached to the forward end of the Centaur. The stub adapter is bolted to the forward ring of the Centaur tank and supports the equipment module and payload fairing. The equipment module attaches to the forward ring of the stub adapter and provides for mounting of the Centaur avionics and the spacecraft adapter.
The payload fairing is a two-half-shell structure constructed of aluminum with vertical, split-line longerons. It consists of a cylindrical section topped by a conical nose cone and a spherical cap.
The fairing provides thermal and acoustic enclosures for the payload and launch vehicle electronic compartments during prelaunch and ascent. Portions of the external surface of the fairing are insulated with cork to limit temperatures to acceptable levels. Non-contaminating thermal control coatings are used on internal surfaces to reduce incident heat fluxes to the spacecraft. Following Atlas booster jettison, the payload fairing is jettisoned.
While coasting in the transfer orbit, the Centaur issues separation commands to release and separate the spacecraft from the forward adapter.
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.
Launch timeline - Chart with times and descriptions of events to occur during the launch.
Ground track - See the trajectory the rocket will follow during its flight.
Atlas index - A directory of our previous Atlas launch coverage.
MISSION STATUS CENTER