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

Quick Facts About the Delta 2000.

- Type: Medium expendable Launch vehicle.

- Origin : United states.

- In service : II: December 7, 1991 - March 16, 1998. IIA: June 10, 1992 - December 5, 2002. IIAS: December 16, 1993 - August 31, 2004.

- Mass : 204,300 kg (450,400 lb).

- Length/Height : 47.54 m (156.0 ft).

- Diameter : 3.04 m (10.0 ft).

- Payload to LEO : 6,580 kg (14,510 lb).

- Payload to GTO : 2,810 kg (6,190 lb).

- Payload to HCO : 806–1,519 kg (1,777–3,349 lb).

- Propellant: Boosters (Atlas IIAS): HTPB. (all) : RP-1 / LOX. First stage: RP-1 / LOX. Second stage: LH2 / LOX. Third stage: N2O4 / MMH.

- Engines: Boosters: (IIAS) 4 Castor 4A solid with thrust of 478.3 kN (107,500 lbf), (all) 2 RS-56-OBA with a thrust of 2,093.3 kN (470,600 lbf), First stage: 1 RS-56-OSA with thrust of 386 kN (87,000 lbf)), Second stage: 2 RL-10A with thrust of 147 kN (33,000 lbf), Third stage(optional): 1 R-4D with thrust of 980 N (220 lbf).

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.

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 LR-105 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 transfer orbit (GTO) 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 II 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.

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