Apollo 10 launched on May 18, 1969, for the ultimate dress rehearsal for a moon landing. The crew would perform every step needed to get to the moon, including undocking the lunar module from the command module and running a simulated descent to less than 50,000 feet (15,243 meters) above the moon's surface.
The aim of the mission was to do a complete dry run for future lunar landings, without actually making it all the way to the surface. As it turned out, being cautious was a wise choice.
The crew of Apollo 10 were among the most experienced astronauts NASA had.
Tom Stafford was the commander of Apollo 10. An Air Force flight test instructor, he was part of the second group of astronauts to join NASA in 1962. He already had two flights of experience behind him: Gemini 6 — which featured the first rendezvous in space with another maneuverable spacecraft — and Gemini 9. He later was commander of the first Apollo-Soyuz mission.
Eugene Cernan, the lunar module pilot of Apollo 10, was aboard Gemini 9 as well. He had done a spacewalk that proved to be very difficult because of the lack of handholds on the Gemini spacecraft. Prior to joining NASA in 1963, he was a Navy aviator. Cernan later became the last Apollo astronaut to walk on the moon as commander of Apollo 17.
John Young, who would pilot the command module, was already a veteran of two Gemini missions: inaugural flight Gemini 3, and commander of Gemini 10. A former Navy test pilot, Young had already performed a docking in space, which would be crucial for Apollo 10. Young later commanded Apollo 16 and was the ninth astronaut to walk on the moon. He also commanded the very first space shuttle launch in 1981 and the ninth space shuttle mission in 1983. Both were aboard Columbia. [Video: John Young: Why We Must Fly in Space]
Aiming for the moon
Some within NASA (including George Mueller, NASA's head of the Office of Manned Space Flight) actually wanted Apollo 10 to go all the way to the surface, according to an account by journalist Andrew Chaikin.
But the plan was vetoed for a couple of reasons. First, Apollo 10's lunar module was too heavy for descent without a last-minute switch to another spacecraft. Second, there were too many unknowns, including the difficulty of predicting the moon's gravitational field.
The initial bit of the mission ran very smoothly. Apollo 10 performed a smaller "first" on the inaugural day of the mission, when it broadcast color video from space for the first time. The video showed the docking between command module Charlie Brown and lunar module Snoopy, as well as the interior of the command module.
A hair-raising moment during descent
In lunar orbit on the fourth day after launch, Cernan and Stafford carefully backed Snoopy away from Charlie Brown. As the crew moved closer to the lunar surface, they exuberantly radioed back reports of what they saw. "We just saw Earthrise and it was magnificent," Cernan said. Minutes later, Stafford and Cernan flew over the future landing site of Apollo 11, taking pictures as they spoke. [Video: Full Dress Run-Through]
But chaos erupted when Snoopy's crew was ready to head back to Charlie Brown. Due to a series of small errors on the crew's part, the ship's guidance system was pointing in the wrong direction. It began to spin — by some accounts wildly — as it flew less than eight nautical miles above the surface.
"Son of a bitch! What the hell happened?" the startled Cernan radioed on an open channel to the world. He and Stafford struggled to get the ship under control before they lost the navigation system altogether, or worse, crashed the ship. After a few heart-racing seconds, the gyrating stopped. In relief, Stafford told Mission Control, "We've got all our marbles."
About five and a half hours after leaving Charlie Brown, Snoopy came within the last 40 miles of docking. The two craft joined up on the far side of the moon; when the crew re-emerged, Stafford radioed, "Snoopy and Charlie Brown are hugging each other."
The first shave
After an exciting few moments near the moon's surface, the crew was glad to relax a bit during the coast back to Earth. They still took the opportunity to do another first: the first shave in space. They used safety razors, a thick shaving gel and a wet cloth to do the work, then displayed their beaming, fresh-shaven visages on the next television show.
"We felt reborn," Cernan later recalled in his autobiography, The Last Man on the Moon.
The crew zoomed back to Earth, reaching a top speed of 24,791 mph (38,897 kph) relative to Earth on re-entry, and splashed down safely on May 26. According to Cernan, the first recovery helicopter to arrive at the command module had a cheery sign drawn on the bottom: "Hello there, Charlie Brown!"
Apollo 10's mission removed the last major obstacle before Apollo 11's landing. Now that NASA had a sense of the difficulties of landing, they felt confident enough to authorize the crew of Neil Armstrong, Buzz Aldrin and Michael Collins to leave Earth only two months later.
That next mission would leave a mark on space history forever.