Centaur was the first American high-energy, liquid hydrogen/liquid oxygen propelled rocket. Developed and launched under the direction of NASA's Lewis Research Center, Cleveland, it became operational in 1966 with the launch of Surveyor 1, the first U.S. spacecraft to soft-land on the lunar surface. Since that time the Centaur upper stage has undergone many improvements.
Until early 1974, Centaur was used exclusively in combination with the Atlas booster. It was subsequently used with a Titan III booster to launch heavier payloads into Earth orbit and interplanetary trajectories.
The Titan IV / Centaur Upper Stage vehicle is manufactured by Lockheed Martin for the Air Force. Centaurís role is to provide the final delivery of the Space Vehicle (payload) into a desired orbit. Centaurís propulsion is supplied by two single-stage, liquid fueled, cyrogenic engines. The Centaur interfaces with the Space Vehicle (SV) via a forward adapter where the avionics, electrical, flight termination, telemetry, and tracking systems are mounted.
PROPULSION SYSTEM: The Centaurís two engines provide thrust via combustion between liquid oxygen and hydrogen and ignite once the Centaur has separated from the core vehicle. Most rockets burn kerosene based hydrocarbon fuels but the Centaur uses a liquid hydrogen [LH2] and liquid oxygen [LOX] propellant combination. The high energy provided by this combination results in a greater specific impulse for the rocket. The propellant utilization system (PU) measures propellant quantities during Centaur operation and controls the propellantís mixture ratio.
The rocket is equipped with two main engines. Designed by Pratt & Whitney Aircraft, each RL10 engine produces 16,500 lbs. of thrust for a total of 33,000 lbs. Many liquid fuel rockets burn some fuel to run a fuel pump but with the RL10 engines this step is eliminated, thereby conserving fuel which instead can be burned to produce added thrust. Another important feature of the RL-10 engines is that they are capable of making multiple starts after long coast periods is space.
STRUCTURAL: The Centaur structural elements include stainless steel LOX and LH2 tanks separated by an intermediate bulkhead (reduces heat transfer between the tanks), main engine mounts, forward and aft adapters for SV and Titan core vehicle mounting, respectively, forward and aft bulkheads which enclose the Centaurís forward and aft ends.
Because the Centaur rocket uses very cold propellants, the tanks require special construction. To prevent the liquid hydrogen from boiling off, Centaur includes a double walled bulkhead which serves as a heat barrier. The liquid hydrogen compartment is covered with light-weight insulation. It protects the tank from the intense aerodynamic heating experienced during the rocket's flight through the earth's atmosphere. The insulation prevents further boil off of the cold fuel inside the tank. The tank is made of very thin stainless steel, less than 200ths of an inch thick. Although the tank is extremely thin, once pressurized, it is light weight yet rigid.
ELECTRICAL SYSTEMS: Initially, the core vehicle provides the electrical power, switching, instrumentation, navigation and control required prior to Centaur separation. After separation, the Centaurís electrical systems take over and perform the following functions throughout flight:
The Centaur D-1AR has an integrated electronic system that performs a major role in checking itself and other vehicle systems before launch and also maintains control of major events after liftoff. The new Centaur system handles navigation and guidance tasks, controls, pressurization and venting, propellant management, telemetry formats and transmission and initiates vehicle events. Most operational needs can be met by changing the computer software.
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