Astronauts Tom Stafford, John Young, and Gene Cernan flew the lunar module to within 8.4 nautical miles of the Moon's surface before firing engines to return to the command module, verifying hardware and procedures for the Apollo 11 landing two months later. Their splashdown in the Pacific closed out a flawless full-dress rehearsal.
Apollo 10 was NASA's final proving flight before attempting an actual Moon landing, and it left almost nothing untested except touching down. The crew undocked the lunar module, nicknamed Snoopy, from the command module Charlie Brown and flew it down to a low orbit, close enough to see boulders and craters that would matter for choosing a landing site.
At one particularly hairy moment, Snoopy's ascent stage began to tumble wildly after a guidance switch was mistakenly left in the wrong position, and Cernan and Stafford briefly fought for control before regaining stability. NASA had deliberately left the lunar module's descent stage fuel tanks partially empty, a safeguard against any temptation to attempt an unauthorized landing.
After reuniting with Young in the command module, the crew fired the engine for a return trajectory and splashed down in the Pacific Ocean, completing an eight-day mission. Every system had performed close enough to expectations that NASA gave the green light for Apollo 11 to attempt the actual landing, a decision vindicated seven weeks later when Neil Armstrong stepped onto the Sea of Tranquility.
Key people: Tom Stafford, John Young, Gene Cernan