Command module KCS

Having heated the command module’s thrusters, the rest of its reaction control system could be primed, ready for use.

Thus far, all small-scale manoeuvres had been carried out using the RCS thrusters on the service module. The command module’s RCS w as a simpler system primarily because there was no need for translation manoeuvres; it was required only to control the spacecraft’s attitude. As re-entry began, it maintained the vehicle in the desired attitude until aerodynamic forces Look over. Then it performed the roll manoeuvres to steer to an accurate landing while simultaneously damping any excessive motions in the pitch and yaw axes. It comprised two entirely independent systems or ’rings’ for complete redundancy, each of which had a fuel Lank and an oxidiser tank mounted in the annular compartment around the periphery of the CM. These supplied propellants to six engines recessed into the outer hull a total of 12 engines, for the majority of the mission, the system was maintained in an inert state with its tanks unpressurised.

Now as they neared re-entry, pyrotechnic squibs were detonated to open valves that fed pressurant from small high-pressure helium tanks to the fuel and oxidiser tanks. Like the RCS systems on the service and lunar modules, the tanks were not pressurised by simply pumping high-pressure gas into them; the helium did not come into contact with the propellant within. In a weightless environment, blobs of liquid in a simple tank are liable to float about with voids in between that could allow gas to enter the propellant lines to the engines. Instead, the propellant was isolated within a Teflon bladder inside the tank, while gas occupied the space around it, squeezing the bladder and forcing propellant through the feed lines to the thrusters.