In June 1987, General Dynamics announced full go-ahead with the Atlas I program, initiating the largest commercial space venture in history. Without a single order, the company announced it would build 18 Atlas I vehicles and intended to market them directly to commercial customers. Atlas I was subsequently selected for three Geostationary Operational Environmental Satellites (GOES) plus two options for NASA, the X-ray Astronomy Satellite for the Italian Space Agency and Ultra-High Frequency (UHF) satellites for the US Navy.
Atlas I consists of the Atlas booster, the Centaur upper stage and the payload fairing. Atlas I is an improved version of the Atlas/Centaur vehicle flown previously for NASA. Basic vehicle structure was strengthened to incorporate a new, larger 14-foot fairing that can accommodate larger spacecraft. An 11-foot fairing is also available. Atlas propulsion is provided by the Rocketdyne MA-5 engine system with two booster engines and one sustainer engine burning a combination of liquid oxygen and RP-1 propellant. Propellant tanks are thin-wall stainless steel. The Atlas I provides a total thrust of 439,338 pounds at liftoff.
Centaur D-1A is powered by two Pratt & Whitney RL-10A-33A turbopump-fed liquid fuel engines burning liquid oxygen and liquid hydrogen. The two engines produce a total thrust of 33,000 pounds. Centaur avionics packages provide control and monitoring of all vehicle functions. The inertial navigation unit (INU) performs the inertial guidance and attitude control computations for both Atlas and Centaur phases of flight and also control Centaur tank pressures and propellant use.
In a typical Atlas launch, the vehicle's booster and sustainer engine are ignited shortly before liftoff. Booster engine cutoff occurs 2 minutes 35 seconds into the flight. The sustainer phase continues until cutoff 4 minutes 35 seconds into the flight followed by separation of the Atlas and Centaur stages. Centaur main engine start occurs seconds after Atlas separation. Centaur has engine restart capability. In a single burn mission, the payload is injected directly into a transfer or circular orbit. In a two-burn mission, the first burn injects the payload into a parking orbit followed by a coast period. The second Centaur burn places the vehicle in the desired orbit, followed by separation of the payload.
The Atlas I stands 138 feet tall with medium fairing, and 144 feet with large fairing, and is 10 feet in diameter. The Atlas core stage is 73 feet long, and the Centaur length is 30 feet. Gross liftoff weight is 360,000 pounds.
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