Atlas II

Atlas II

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)[1]
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[1]
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.

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 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.[2] The Vernier engines on the first stage of the Atlas I were replaced by a hydrazine fueled roll control system.[3]

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.

Versions

Atlas II

The original Atlas II was based on the Atlas I and its predecessors. This version flew between 1991 and 1998.[3]

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.[4] The IIA version flew between 1992 and 2002.[5]

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.[4] IIAS was used between 1993 and 2004, concurrently with IIA.[6]

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, California.

Atlas launch vehicle evolution. (USAF)

See also

References

  1. 1 2 Tariq Malik "Final Atlas 2 Rocket Orbits Classified U.S. Satellite", Space News, August 31, 2004 (Accessed 24 Sept 2014)
  2. ↑ "Atlas IIA(S) Data Sheet". Space Launch Report. Retrieved 9 January 2016.
  3. 1 2 "Atlas II". Astronautix. Retrieved 9 January 2016.
  4. 1 2 "Atlas Launch System Payload Planner's Guide" (PDF). Lockheed Martin. Retrieved 9 January 2016.
  5. ↑ "Atlas IIA". Astronautix. Retrieved 9 January 2016.
  6. ↑ "Atlas IIAS". Astronautix. Retrieved 9 January 2016.
  7. ↑ Spaceflight Now, Atlas IIAS (accessed 24 Sept 2014)
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