On 21 May 1969, the crew of Apollo 10 entered their circularized orbit of 113.9 km by 109.1 km around the Moon after two Service Propulsion System burns. Aboard the Command Module (CM) Charlie Brown were mission Commander Thomas P. Stafford, CM Pilot John Young and Lunar Module (LM) Pilot Eugene Cernan. This mission was the first "all up" test of the Apollo spacecraft system that would eventually land on the Moon, including the Lunar Module. The stated mission of Apollo 10 was to "demonstrate crew, space vehicle and mission support facilities during a manned lunar mission and to evaluate LM performance in cislunar and lunar environment." It was designed to duplicate every event of the historic Apollo 11 landing, except the landing itself. On 22 May, Stafford and Cernan entered the Lunar Module Snoopy, which then separated from the Command Module and prepared to descend to 14 km above the lunar surface. In a critical phase just prior to firing the ascent stage after separating from the descent stage, an incorrectly set navigation system switch triggered the Reaction Control System (RCS) into trying to compensate, causing the Lunar Module to tumble out of control.
"Gimbal lock!" Stafford barked. This would result in the loss of the navigation platform and was potentially catastrophic. They fought to regain control of the spacecraft, even as it spun and jerked from the mixed signals fed by the navigation radar to the RCS, and together they brought the LM under control. They proceeded with the ascent stage firing and Stafford and Cernan successfully rendezvoused with John Young in the CM. It had been a heart-stopping moment, but one that experienced pilots and astronauts like Stafford and Cernan were equipped to handle. They had averted a disaster that could have sent the Lunar Module crashing into the surface of the Moon, killing the crew and dashing America's goal of landing men on the Moon and returning them safely to Earth. Their cool thinking and fast responses saved the mission. Apollo 10 achieved all its goals and kept America on track for landing Neil Armstrong and "Buzz" Aldrin on the Moon in the summer of 1969.
For Cernan, the Moon had come so tantalizingly close. But he would one day return to the Moon, and not only walk on its surface, but drive there, just as Wernher von Braun had predicted.
Apollo 17 Lunar Module Challenger is prepared for stowage inside the Spacecraft Lunar Module Adapter of its Saturn V after having completed its final checkout inside the Manned Spacecraft Operations Building at Kennedy Space Center. LRV-3 is visible behind and to the right of the crew ladder. (NASA)
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