Plummet

At 18 kilometres altitude, the cabin pressure relief valve was set for entry. In this mode, the valve held the cabin pressure at its nominal value until the outside pressure rose to a slightly higher level, at which point outside air would begin to flow into the cabin. On the main display console in front of the CMP and commander was a small altimeter whose needle now responded to the rising outside air pressure, allowing the crew to use its information to check the progress of the descent.

In preparation for the intensive sequence of pyrotechnic events to come, the SECS was again armed which also gave the crew the option of dealing with a possibly unstable plummeting spacecraft by manually deploying the drogue chutes early.

Ten kilometres up and falling, they switched on the logic system that would automatically trigger the components of the Earth landing system. It used timers and barometric switches to orchestrate the deployment of a series of parachutes and other events to bring the command module to a safe meeting with the ocean’s surface. They also threw a switch to finally disable the RCS thrusters. Next, 7,300

Diagram of the components of the Earth landing system at the apex of the CM. (NASA)

metres up and descending at over 150 metres per second, a barometric switch operated to jettison the upper section of the conical hcatshield, commonly referred to as the apex cover. Four gas-operated pistons pushed it off and a small parachute attached to it slowed it down to take it away from the descending command module. This exposed two canisters containing the drogue chutes and the main parachutes packed around the tunnel. As with all the automatic events about to occur over the next few minutes, a guarded pushbutton allowed the crew to deploy the apex cover should the automatic system fail.

Once the apex cover had enough time to clear. 1.6 seconds to be exact, two drogue chutes were fired away from the spacecraft by pyrotechnic mortars to ensure that they avoided the turbulent airflow’ directly above the plummeting spacecraft.

“Stand by for the drogues.” called Young as Charlie Broun continued descending.

“Stand by. There went something,” said Stafford.

“God damn!” cried Cernan. "There’s the drogues! There they are, babe.”

“God damn, we’re on the drogues,” affirmed Young. “Rock, rock, old baby; rock. rock. This son of a gun.”

These parachutes were designed to reduce the CM’s descent speed to 80 metres per second. By now, the crew expected to see their cabin pressure rise as the planet’s air flowed in from outside via the cabin pressure relief valve. If not, the crew could set the valve to its dump position.

“There wasn’t much of a rotation as the drogue chutes deployed.” explained Aldrin after his flight. "They seemed to oscillate around a good bit. but did not transmit much of this oscillation to the spacecraft. The spacecraft seemed to stay on a pretty steady course.”

The proper operation of the Farth landing system was of particular concern to the Apollo 12 crew’, given that their spacecraft had sustained two lightning strikes during its launch ten days earlier. They had no means of knowing w’hether the surges of electricity had damaged the pyrotechnic devices that would bring the crew to a safe landing, except by firing them.

"Stand by for drogues,” called Gordon. They w’ere keenly watching the event timer to see if events occurred on time.

"What’s the time on the clock? 8:04?" asked Conrad.

The entry PAD had predicted that they should expect deployment of the drogue chutes 8 minutes 4 seconds after entry interface. That time had just passed and there was no deployment. Gordon began to count out loud.

"8:12, 13. 8:14.” Ten seconds had passed, the spacecraft had fallen a further kilometre and a half and still there were no drogue chutes.

“8:15, 16.” continued Gordon.

Unlike the predictions of trajectories in space, wdiere New’tonian mechanics affords great precision, re-entry predictions are subject to the vagaries of the atmosphere and how its density acts to slow the spacecraft. Moreover, entry interface w’as an entirely arbitrary point with little relationship to the atmosphere. But it was all the crew had to go on. Gordon kept counting.

‘’8:18. There go the drogues!’-

“’There it goes,– confirmed Conrad in relief.

“Good show,’- added Bean who passed on the news to mission control. “We got drogues, Houston.– He added for his crewmates. “Man. This is hauling it. isn’t it?”