NASA's Apollo missions in the 1960s had one goal, to get to the moon before the decade was out, as President Kennedy had stated. Each Apollo flight made concrete steps toward that goal. On July 20, 1969, Neil Armstrong and Buzz Aldrin touched down on the surface in the lunar lander Eagle, and then stepped onto the surface. Everyone knows that. But what about Apollo 10, which left for the moon on May 18, 1969? Commander Thomas P. Stafford, Command Module Pilot John W. Young, and Lunar Module Pilot Eugene A. Cernan orbited the moon as a "dress rehearsal" for the planned moon landing. Yes, they had a Lunar Module (named Snoopy), which separated from the Command Module (named Charlie Brown) and headed toward the moon. But they were under orders to stop at 47,000 feet above the lunar surface and return to the ship, and then to earth. They went such a long way to stop short of the goal, which couldn't have been easy.
But Snoopy didn’t have enough fuel to land on the moon and then blast off again. According to Craig Nelson, author of the book “Rocket Men,” Cernan speculated that the lander’s ascent module had been short-fueled on purpose: “A lot of people thought about the kind of people we were: ‘Don’t give those guys an opportunity to land, ‘cause they might!’”
Read about the mission that worked out the last kinks for the moon landing at the New York Times. -via Damn Interesting