The first extended use of the Service Propulsion System engine on the Command and Service module was for the Lunar Orbit Insertion (LOI) burn.
Mitchell kept his plan a secret from NASA, knowing that the agency would be completely unreceptive to the idea. He said nothing about it to his crewmates. The test subjects had also agreed to keep quiet.
“Houston, Tranquillity Base here. The Eagle has landed.”
Suddenly, Buzz and Neil heard the high-pitched sound of the Master Alarm. On the computer display the “PROG” light glowed amber. “Program alarm,” Armstrong radioed. Quickly, Aldrin queried the computer for the alarm code, and “1202” flashed on the display.
The machine-like performance of flight crew and ground controllers continued. Each participant was in perfect harmony with the other, moving to a cadence dictated by the laws of physics and the clock.
Docking was a delicate maneuver, since both ships were traveling at nearly five miles per second, but the docking mechanism itself was one of the simplest on the entire spacecraft, and the docking procedure had been perfected on previous Apollo flights, none of which experienced any significant problems with docking.
“The approaching dusk and the damp mistiness left by the now-departed rainstorm only enhanced the spectacular sight and the sound of the launch. Tentacles of flame erupted on either side of the bottom of the Saturn V, which seemed to sit in its own cauldron of fire momentarily before breaking free of its shackles, as four hold-down arms at the base of the launch pad and five access arms along the outside of the booster swung away.” (Smoke Jumper, Moon Pilot by Willie Moseley)