Ejection: freeing the lander

The final stage of the TD&E process was the ejection of the lunar module from the S – IVB, which was not simply a process of throwing a switch and then watching it happen. Throwing the switch would come at the end, but first they had to feed the signal from the switch in the CM down past the LM to the pyrotechnically-fired spring thrusters on the SLA that would push the LM free. That meant that the CMP had to connect two umbilical cables to feed power and signals between the two spacecraft. However, to do that he had to get into the tunnel, which is a short void between the command module’s forward hatch and the lunar module’s overhead hatch. Immediately after the docking, the space within the tunnel was still a vacuum so the CMP had therefore to bleed oxygen from the CM into the void and, in doing so, he also fed it into the LM cabin. Prior to launch, the dump valve in the LM’s overhead hatch was left open in order that, as the Saturn V lofted both spacecraft to orbit, the mixed atmosphere within the LM was gradually exhausted, leaving the interior essentially a vacuum, ready to be filled with oxygen. By docking with the LM, the tunnel had been placed over the hatch and its dump valve. Once the pressure on both sides of the forward hatch had equalised, the hatch itself could be removed, the umbilicals could be connected to feed power to the pyrotechnic devices for freeing the LM, and a check could be made to ensure that all twelve latches had properly engaged. Finally, the switch could be thrown to eject the LM from the S – IVB and allow the Apollo stack to continue its journey to the Moon.

None of these steps were simple, as each had its own checklist of items that had to be set or verified to ensure that the crew did not configure the spacecraft in a way that might endanger their lives. The process was carried out in a slow, methodical fashion of checks, verification and cross-checks: forty minutes work to allow them finally to throw one switch.