As Apollo missions go it had been an
uneventful flight. The mission's accomplishments were ticking off the flight
plan like seconds on a well tuned clock.
Apollo 10, the second lunar voyage, was that "in between" flight that the public seems to forget due to the accomplishment of Apollo 8 in first reaching the Moon and Man's first landing on another world during Apollo 11. Even so, this flight was groundbreaking in that this was the first time the lunar module (LM) would be used in lunar orbit. The LM, as the craft would be nicknamed, would take Thomas Stafford and Eugene Cernan to within 50,000 feet of the lunar surface. That close approach would mimic every operational objective of a landing with the exception of the final descent.
The mission was deemed a dress rehearsal, but, in hindsight, Apollo 10 was a test pilot's dream of a "full up" mission and everything was going smoothly.
At 102:45:12 GET (Ground Elapsed Time) having completed their orbital descent to 50,000 feet, Stafford and Cernan prepared to jettison the Descent Stage and fire the Ascent Stage engine in order to rendezvous with the Command Module (CM) piloted by John Young, which was waiting in a parking orbit 50 miles above the lunar surface. It was a normal maneuver and successfully performed in Earth orbit during the Apollo 9 mission.
Suddenly, the LM tumbled out of control. While still on a hot mike, with the world listening, Gene blurted out, "Son of bitch, what the hell happened!"
Gene Cernan would later say, "I saw the lunar horizon go by about seven or eight times in ten seconds. That's a hair raising experience. That's when I said, "Son of bitch, what the hell happened."
Tom Stafford jettisoned the Descent Stage of LM and maneuvered to regain control of the gyrating Ascent Stage. After only 8 seconds, Tom, in a masterful feat of flying, had the LM under control. Tom and Gene guided the LM to a successful rendezvous with the CM in lunar orbit.
What caused this severe tumbling of the LM while in low lunar orbit? During an interview Gene described what happened during those critical moments.
"When we staged, there were a number of things we had to do, including changing programs in the PGNS (Primary Guidance and Navigation System) and changing switch positions. When it came time to stage... there was (a) switch that had to be changed and I changed it. I will bet that Tom acknowledged (the same instructions) and moved it back to the old one (the original position). And, in effect, we created the problem."
Tom and Gene followed prescribed procedures that were based upon years of training, but even then, they needed some device to provide step by step instructions.
What they used were cue cards. Small pieces of cardboard with important instructions printed in sequential order. These cue cards were small and fitted with Velcro for attachment to critical areas on the LM instrument panel. The photograph above shows Tom and Gene working in the LM simulator. You can see some of these cue cards on the main instrument panel. They provided a quick reference for key actions during specific events in the flight.
During a meeting with Gene in San Antonio during 2004, he told his assistant, Claire Johnson, and me, that the cue cards were extremely important during a mission. Gene related to us that the cue cards were right in front of their eyes and they referred to them frequently at critical times.
I had purchased several cue cards from Captain Cernan's collection. As I showed him the cards, he picked this particular card out and pointed to a specific command on the card. The command was "AGS MODE CONT - AUTO." Gene went on to relate how this was the command that he and Tom both handled that caused the LM to gyrate in low lunar orbit.
The failure to flip the switch to "AGS MODE CONT - AUTO" or Abort Guidance Control to Automatic caused the LM to start searching for the CM prematurely. The rendezvous radar was commanded to lock onto the CM. The LM attempted to position the radar to find the CM, which was not in range, by maneuvering around on its three axes and caused Tom and Gene's wild ride.
In the above two pictures, the command has been highlighted in yellow on both sides of the cue card to provide a better view of the instruction.
This cue card was flown on Apollo 10 and was key to the only major incident that occurred on the mission. Gene had already written "Apollo X, Gene Cernan" on the card as provenance that this artifact was part of his personal collection.
While in San Antonio, Gene took the time to pose with the cue card during our interview.
Gene would later tell me that his inopportune outburst triggered by a potential brush with disaster caused him some grief when he returned to Earth. A pastor from Florida had heard the outburst and wrote to NASA to chastise Gene for his poor choice of words.
I can only wonder what I would have said if I was in Gene's shoes at that moment. I know it would have been worse or, at the very least, more colorful.