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Titan IV Centaur Upper Stage

• Length: 29ft
• Diameter: 14ft
• Propulsion: 2 Pratt&Whitney RL 10A-3-3A
• Propellant: LH₂ and LO₂
• Thrust: 33,000lbs (16,500lbs each engine)
• ISP: 444sec Vac

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.

STRUCTURAL: The Centaur structural elements include stainless steel LO2 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.

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. The propellant utilization system (PU) measures propellant quantities during Centaur operation and controls the propellant's mixture ratio.

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: 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.