May 21, 1969: Apollo 10 was a human spaceflight, the fourth crewed mission in the United States Apollo program, and the second (after Apollo 8) to orbit the Moon. It was the F mission: a “dress rehearsal” for the first Moon landing, testing all the components and procedures just short of actually landing. While astronaut John Young remained in the Command Module orbiting the Moon, astronauts Thomas Stafford and Gene Cernan flew the Apollo Lunar Module (LM) “Snoopy” to a descent orbit within 8.4