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Centaur Upper Stage

centaur 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. Centaur's role is to provide the final delivery of the Space Vehicle (payload) into a desired orbit. Centaur's 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 Centaur's 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 propellant's 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 Centaur's 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 Centaur's 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.

  • Guidance, Navigation and Control (GN&C): Centaur's guidance and navigation subsystem provides autonomous flight guidance and orientation. The vehicle's position and velocity are determined using attitude and rate data measured by the inertial navigation unit (INU) and the INU's flight control subsystem and inertial measurement system (IMS). The INU uses three ring laser gyros (RLGs), one per axis, which replace conventional spinning masses for these measurements. A sequence control unit (SCU) initiates discrete in-flight events including main engine start (MES), main engine cutoff (MECO), and vehicle rolls via exterior thrusters.

  • Telemetry, Tracking, and Command System: The telemetry system is responsible for encrypting the Centaur Pulse Code Modulation (PCM) telemetry signal, formatting and encoding the encrypted signal, and modulating the signal for transmission. The transmission is made by an RF link to a telemetry ground station or an Air Force Satellite Control Facility Remote Tracking Station (AFSCF-RTS). The tracking system provides the necessary data to determine core and Centaur position in support of the flight termination systems. Telemetry systems work in conjunction with GN&C systems.

  • Flight Termination System (FTS): The Titan IV Centaur configuration has two independent Range Safety Commanded encrypted, FTSs. One in the Titan IV Stage II and one on the Centaur forward adapter. These independent systems each function upon receipt of the same ground station destruct command signal. The Range Safety Officer (RSO) has the option to command Titan IV core engine shutdown or Titan IV core, SRM/SRMUs and Centaur propellant vessel destruct. The RSO is provided vehicle flight path information from Centaur transponder tracking, vehicle skin radar and vehicle guidance data. If the TIV/Centaur vehicle deviates from the planned flight path corridor, the RSO can employ the FTS.

  • Electrical Power: The Centaur Airborne Electrical Power System provides electrical power to the Centaur's components from the time ground power is removed during countdown until end of mission. The electrical power system provides independent power sources for the core vehicle, the FTS, ordnance devices, Centaur, and the SV (until SV separation) in the form of main vehicle batteries, FTS batteries, and payload batteries.

Centaur I 10 30 30,000 33,000 444.4
Centaur II 10 33 37,000 33,000 444.4
Centaur IIA 10 33 37,000 41,600 449.4
Titan IV Centaur 14.2 29.1 46,000 33,000 444.4


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