Early Exploration of the Moon by Tom Lund

Author:Tom Lund
Language: eng
Format: epub
ISBN: 9783030020712
Publisher: Springer International Publishing

Reaction Control System in Command Module

The reaction control system in the Command Module enabled attitude control after the Command Module separated from the Service Module just before reentering the earth’s atmosphere. Attitude of the spacecraft relative to the velocity vector was critical for successful entry into the atmosphere.

The Command Module contained two independent reaction control subsystems for redundancy referred to as subsystem 1 and subsystem 2. Each subsystem had a separate set of six rocket engines directed to provide clockwise roll, counterclockwise roll, +pitch, −pitch, +yaw, and -yaw.

The reaction engines were 11.7 inches long, and the nozzle exit diameter was 2.13 inches. Each engine generated 93 pounds of thrust. The engines were mounted internally with exits of the engines flush with the outer surface of the Command Module. Since the engines were mounted internally, they were ablatively cooled and that limited their operating life. The engines, which were rated for service life of 200 seconds and 3,000 operational cycles, were developed and built by the Rocketdyne Division of North American Aviation.

The engines used monomethyl hydrazine (MMH) for fuel and nitrogen tetroxide (N2O4) as the oxidizer. This combination ignited upon contact with one another. Each of the two redundant reaction systems had a fuel tank, an oxidizer tank, and a helium tank. Helium was used to pressurize the fuel and oxidizer. The helium tank was about 9 inches in diameter and contained helium at a pressure of 4,150 psi. A pressure regulator reduced the pressure to about 180 psi to pressurize the fuel and oxidizer tanks.

Fuel was contained in cylindrical tanks 17 inches long and 12.5 inches in diameter with hemispheric domes. The tanks were built out of titanium alloy. Each tank held 45 pounds of fuel. The oxidizer tank was similar to the fuel tank but 3 inches longer at 20 inches long. Each oxidizer tank held 89 pounds of oxidizer. The tanks had Teflon bladders that held the fuel and oxidizer. When helium pressure was applied to the tanks, it squeezed the bladder and forced the propellants into manifolds that fed the engines.

The fuel and oxidizer lines connected to feed injector valves near each engine. The injector valves were spring loaded closed, and they were opened to admit propellants by energizing solenoid coils. There were two sets of coils in each injector, one for automatic control and one for direct control from the hand rotational controller. Control signals for the automatic solenoid coils were generated by the Reaction Jet Engine ON-OFF Control Assembly (RJ/EC).

The engines could be pulse fired for short impulses lasting less than 70 milliseconds or fired continuously for several seconds. Input signals from the guidance computer instructed operation of the RJ/EC when the spacecraft was under computer control, and signals from the Electronic Control Assembly instructed operation of the RJ/EC when the spacecraft was being controlled by the stabilization and control system.

A backup manual control mode could be selected by the astronauts by turning the “Direct RC” switch on the instrument panel to the ON position.

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