The Apollo 11 mission was the first manned lunar landing. It was the fifth manned mission in the Apollo program.
The first Apollo landing site, in the southern Sea of Tranquility about 20 km (12 mi) southwest of the crater Sabine D, was selected in part because it had been characterized as relatively flat and smooth by the automated Ranger 8 and Surveyor 5 landers, as well as by Lunar Orbiter mapping spacecraft, and therefore unlikely to present major landing or EVA challenges. Armstrong bestowed the name ‘Tranquillity Base’ on the landing site immediately after touchdown.
On July 20, 1969, while on the far side of the Moon, the lunar module, called “Eagle,” separated from the Command Module, named “Columbia”. Collins, now alone aboard Columbia, carefully inspected Eagle as it pirouetted before him. Soon after, Armstrong and Aldrin fired Eagle’s engine and began their descent. They soon saw that they were “running long”; Eagle was 4 seconds further along its descent trajectory than planned, and would land miles west of the intended site. The LM navigation and guidance computer reported several “program alarms” as it guided the LM’s descent. These alarms tore the crew’s attention away from the scene outside as the descent proceeded. In NASA’s Mission Control Center in Houston, Texas, a young controller named Steve Bales was able to tell the flight director that it was safe to continue the descent in spite of the alarms. Once they were able to return their attention to the view outside, the astronauts saw that their computer was guiding them toward a landing site full of large rocks scattered around a large crater. Armstrong took manual control of the lunar module at that point, and guided it to a landing at 4:17 p.m. Eastern Daylight Time on July 20 with less than 30 seconds’ worth of fuel left.
The program alarms were “executive overflows”, indicating that the computer could not finish its work in the time allotted. The cause was later determined to be that the LM rendezvous radar was left on during the descent, causing the computer to spend unplanned time servicing the unused radar. Steve Bales received a Medal of Freedom for his “go” call under pressure.
At 2:56 UTC, six and a half hours after landing, Armstrong made his descent to the Moon surface and took his famous “one giant leap for mankind.” Aldrin joined him, and the two spent two-and-a-half hours drilling core samples, photographing what they saw and collecting rocks.
After describing the surface (“very fine grained… almost like a powder”), Armstrong stepped off Eagle’s footpad and into history as the first human to set foot on another world. He reported that moving in the Moon’s gravity, one-sixth of Earth’s, was “perhaps even easier than the simulations.”
During this period Mission Control used a coded phrase to warn Armstrong that his metabolic rates were high and that he should slow down. He was moving rapidly from task to task as time ran out. Rates remained generally lower than expected for both astronauts throughout the walk, however, so Mission Control granted the astronauts a 15 minute extension.
After more than 21½ hours on the lunar surface, they returned to Collins on board “Columbia,” bringing 20.87 kilograms of lunar samples with them. The two Moon-walkers had left behind scientific instruments such as a retroreflector array used for the Lunar Laser Ranging Experiment. They also left an American flag and other mementos, including a plaque bearing two drawings of Earth (of the Western and Eastern Hemispheres), an inscription, and signatures of the astronauts and Richard Nixon. The inscription read:Here Men From Planet EarthFirst Set Foot Upon the MoonJuly 1969 A.D.We Came in Peace For All Mankind.
The astronauts returned to earth on July 24, welcomed as heroes. The splashdown point was 13°19′N 169°9′W, 400 miles (640 km) SSW of Wake Island and 24 km (15 mi) from the recovery ship, USS Hornet.