Atlas IIa
Launch of an Atlas II rocket
|
|
| Function | Medium expendable Launch vehicle |
|---|---|
| Manufacturer | Lockheed Martin |
| Country of origin | United States |
| Size | |
| Height | 47.54 m (156 ft) |
| Diameter | 3.04 m (10 ft) |
| Mass | 204,300 kg (414,000 lb) |
| Stages | 3.5 |
| Capacity | |
| Payload to LEO | 6,580 kg |
| Payload to GTO |
2,810 kg |
| Associated rockets | |
| Family | Atlas |
| Launch history | |
| Status | Retired |
| Launch sites |
SLC-36, Cape Canaveral SLC-3 Vandenberg AFB |
| Total launches | 63 (II: 10, IIA: 23, IIAS: 30) |
| Successes | 63 (II: 10, IIA: 23, IIAS: 30) |
| First flight |
II: 7 December 1991 IIA: 10 June 1992 IIAS: 16 December 1993 |
| Last flight |
II: 16 March 1998 IIA: 5 December 2002 IIAS: 31 August 2004 |
| Notable payloads |
SOHO (Atlas IIAS) TDRS (Atlas IIA) |
| Boosters (Atlas IIAS) - Castor 4A | |
| No. boosters | 4 |
| Engines | 1 Solid |
| Thrust | 478.3 kN (107,530 lbf) |
| Specific impulse | 266 sec |
| Burn time | 56 seconds |
| Fuel | Solid |
| Boosters (all) - MA-5A | |
| No. boosters | 1 |
| Engines | 2 RS-56-OBA |
| Thrust | 2,093.3 kN (470,680 lbf) |
| Specific impulse | 299 sec |
| Burn time | 172 seconds |
| Fuel | LOX/RP-1 |
| First stage | |
| Engines | 1 RS-56-OSA |
| Thrust | 386 kN (86,844 lbf) |
| Specific impulse | 316 sec |
| Burn time | 283 seconds |
| Fuel | RP-1/LOX |
| Second stage - Centaur | |
| Engines | 2 RL-10A |
| Thrust | 147 kN (41,592 lbf) |
| Specific impulse | 449 sec |
| Burn time | 392 seconds |
| Fuel | LH2/LOX |
| Third stage - IABS (optional) | |
| Engines | 1 R-4D |
| Thrust | 980N (220 lbf) |
| Specific impulse | 312 sec |
| Burn time | 60 seconds |
| Fuel | N2O4/MMH |
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 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 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 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.
The original Atlas II was based on the Atlas I and its predecessors. This version flew between 1991 and 1998.
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