Apollo 10 was a May 1969 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. Astronauts Thomas Stafford and Gene Cernan flew the Apollo Lunar Module (LM) to a descent orbit within 8. 4 nautical miles (15. 6 km) of the lunar surface, the point where powered descent for landing would begin. After orbiting the Moon 31 times Apollo 10 returned safely to Earth, and its success enabled the first actual landing (Apollo 11) two months later.