crews would be. They were flown to Pago Pago International Airport in Tafuna for a greeting reception, before boarding a C-141 cargo plane to Ellington Air Force Base near Houston. Aftermath Orbital operations and the solo maneuvering of the LM in partial descent to the lunar surface paved the way for the successful Apollo 11 lunar landing by demonstrating the capabilities of the requisite mission hardware and systems. Among other items, the crew demonstrated that the tasks required to execute the checkout procedures of the LM and initial descent and rendezvous were feasible to accomplish within the allotted time, that the communication systems of the LM were sufficient, that the rendezvous and landing radars of the LM were operational in lunar orbit, and that the two spacecraft could be adequately monitored by personnel on Earth. Additionally, the precision of lunar orbital navigation improved with Apollo 10 and, combined with data from Apollo 8, NASA expected that it had achieved a level of precision sufficient to execute the first crewed lunar landing. After about two weeks of Apollo 10 data analysis, a NASA flight readiness team cleared Apollo 11 to proceed with its scheduled July 1969 flight. On July 16, 1969, the next Saturn V to launch carried the astronauts of Apollo 11, Neil Armstrong, Buzz Aldrin and Michael Collins. On July 20, Armstrong and Aldrin landed on the Moon, and four days later the three astronauts returned to Earth, fulfilling John F. Kennedy's challenge to Americans to land astronauts on the Moon and return them safely to Earth by the end of the 1960s. In July 1969, Stafford replaced Alan Shepard as Chief Astronaut, and then became deputy director of Flight Crew Operations, under Deke Slayton. In his memoirs, Stafford wrote that he could have put his name back in the flight rotation, but wanted managerial experience. In 1972, Stafford was promoted to brigadier general and assigned as commander of the American portion of the Apollo–Soyuz Test Project, which flew in July 1975. He commanded the Air Force Flight Test Center at Edwards Air Force Base in California, retiring in November 1979 as a lieutenant general. Young commanded the Apollo 16 lunar landing mission flown in April 1972. From 1974 to 1987, Young served as Chief Astronaut, commanding the STS-1 (1981) and STS-9 (1983) Space Shuttle missions in April 1981 and November 1983, respectively, and retired from NASA's Astronaut Corps