FLIGHT CONTROL SYSTEM

Flight control of the second stage is maintained by gimbaling the four rocket thrust engines for thrust vector (direction) control. These are the four out­

board engines; the fifth J-2 engine located in the center of the cluster is stationary.

Each outboard engine has a separate engine actua­tion system to provide the force to position the en­gine. Gimbaling is achieved by hydraulic-powered actuators controlled by electrical signals generated through a flight control computer located in the instrument unit just above the third stage. Hydrau­lic power for operating each of the gimbaling actu­ators is supplied by individual engine-driven hy­draulic pumps. Each system is self-contained and operates under a pressure of 3,500 psi. The compon­ents of each hydraulic system are attached to the thrust structure above each of the outboard engines. The main hydraulic pump is driven by the liquid oxygen turbopump on the respective engine. Two servoactuators that control each engine programmed for gimbaling are located on the engine outboard side. One is on the pitch plane, and the other on the yaw plane. Each actuator will gimbal the en­gine plus or minus 7 degrees in pitch or yaw and plus or minus 10 degrees in combination to correct for roll errors at a minimum rate of 8 degrees per second.

During flight, the guidance system continuously determines an optimum vehicle steering command based on the vehicle’s position, velocity, and accel­eration. This system, located in the instrument unit, has a guidance signal processor which de­livers attitude correction signals to the flight con­trol computer in the instrument unit. These signals are shaped, scaled, and summed electronically. These summed error signals are then directed to the servoactuator amplifiers, which, in turn, drive their respective servoactuators in the second stage. These signals cause the servoactuators to position the engines.

MEASUREMENT SYSTEM

A wide variety of transducers and signal condi­tioners is used in the instrumentation system, which feeds signals to a high-level telemetering system for transmission to the ground. The various instru­mentation sensors monitor pressure, temperature, and propellant flow rates within the tanks. Other sensors record the amount of vibration and noise, and flight position and acceleration.

Tied into the measurement system are telemetry and radio frequency subsystems which transmit the performance signals to ground receiving sta­tions for immediate (real-time) and postflight ve­hicle performance evaluation. Antennas which serve the telemetry and radio frequency subsystems are flush-mounted on the forward skirt and are omni­directional in coverage.

Approximately 10 seconds before second stage pro­pellant depletion, a signal activates the separation system which will sever the second stage from the third. An interstage connecting the second and third stage has four retrorockets which are fired to decel­erate the second stage.