Atlas II

Atlas II was a member of the Atlas family of launch vehicles, which evolved from the successful Atlas missile program of the 1950s. It was designed to launch payloads into low earth orbit, geosynchronous transfer orbit or geosynchronous orbit. Sixty-three launches of the Atlas II, IIA and IIAS models were carried out between 1991 and 2004; all sixty-three launches were successes, making the Atlas II the most reliable launch system in history. The Atlas line was continued by the Atlas III, used between 2000 and 2005, and the Atlas V which is still in use.

Design
Atlas II provided higher performance than the earlier Atlas I by using engines with greater thrust and longer fuel tanks for both stages. LR-89 and RS-27 were replaced by the RS-56, derived from the RS-27. The total thrust capability of the Atlas II of 490,000 pounds force (2,200 kN) enabled the booster to lift payloads of 6,100 pounds (2,767 kg) into geosynchronous orbit of 22,000 miles (35,000 km) or more. Atlas II was the last Atlas to use a three engine, "stage-and-a-half" design: two of its three engines were jettisoned during ascent, but its fuel tanks and other structural elements were retained. The two booster engines, RS-56-OBAs, were integrated into a single unit called the MA-5A and shared a common gas generator. They burned for 164 seconds before being jettisoned. The central sustainer engine, an RS-56-OSA, would burn for an additional 125 seconds. The Vernier engines on the first stage of the Atlas I were replaced by a hydrazine fueled roll control system.

This series used an improved Centaur upper stage, the world’s first cryogenic propellant stage, to increase its payload capability. Atlas II also had lower-cost electronics, an improved flight computer and longer propellant tanks than its predecessor, Atlas I.

Atlas II
The original Atlas II was based on the Atlas I and its predecessors. This version flew between 1991 and 1998.

Atlas IIA
Atlas IIA was a derivative designed to service the commercial launch market. The main improvement was the switch from the RL10A-3-3A to RL10A-4 engine on the Centaur upper stage. The IIA version flew between 1992 and 2002.

Atlas IIAS
Atlas IIAS was largely identical to IIA, but added four Castor 4A solid rocket boosters to increase performance. These boosters were ignited in pairs, with one pair igniting on the ground, and the second igniting in the air shortly after the first pair separated. The half-stage booster section would then drop off as usual. IIAS was used between 1993 and 2004, concurrently with IIA.

Background
In May 1988, the Air Force chose General Dynamics (now Lockheed-Martin) to develop the Atlas II vehicle, primarily to launch Defense Satellite Communications System payloads and for commercial users as a result of Atlas I launch failures in the late 1980s. Led by lead engineer Samuel Wagner, the Atlas II was crucial to the continued development of the United States' space program.

Atlas IIs were launched from Cape Canaveral Air Force Station, Fla., by the 45th Space Wing. The final West Coast Atlas II launch was accomplished December 2003 by the 30th Space Wing, Vandenberg AFB, Calif.


 * General Characteristics
 * Primary function: Launch vehicle
 * Primary contractor: Lockheed Martin - airframe, assembly, avionics, test and systems integration
 * Principal subcontractors: Rocketdyne (Atlas engine, MA-5); Pratt & Whitney (Centaur engine, RL-10) and Honeywell & Teledyne (avionics)
 * Power Plant: Three MA-5A (RS-56) Rocketdyne engines, two Pratt & Whitney RL10A-4 Centaur engines
 * Thrust: 494,500 lbf (2,200 kN)
 * Length: Up to 156 ft (47.54 m); 16 ft (4.87 m) high engine cluster
 * Core Diameter: 10 feet (3.04 m)
 * Gross Liftoff Weight: 414,000 lb (204,300 kg)
 * First Launch: February 10, 1992
 * Models: II, IIA, and IIAS
 * Launch Site: Cape Canaveral AFS, Florida