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 geosynchronous 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
The Centaur propulsion system uses two RL10A-4-1B engines with extendible nozzles manufactured by Pratt & Whitney. Each engine is has a rated thrust of about 22,000 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 target orbit, the Centaur issues separation commands to release and separate the spacecraft from the payload adapter.
MISSION STATUS CENTER