With Armstrong, Aldrin, and Collins secured in the capsule, the mighty Saturn V rocket was slated to lift off from the now-historic launchpad 39A, and the countdown began in the early morning. At 9:32 a.m. EDT, the rocket ignited, and Apollo 11 lurched upward with millions watching. The mission to land on the Moon was underway.
The launch was picture-perfect, and within 12 minutes the craft entered Earth orbit at an altitude of about 100 nautical miles (185 kilometers). After an orbit and a half, the third-stage engine fired and moved the spacecraft into a trans-lunar injection, sending it toward our celestial neighbor. Some 30 minutes later, the crew performed the maneuver that separated the command/service module from the spent rocket stage and allowed docking with the LM. After the rocket stage was discarded, the command module and the LM headed moonward.
The cruise to the Moon lasted three days, and by July 19, the craft passed close enough to the Moon to fire its propulsion engine, setting it on a course to orbit the Moon. Armstrong, Aldrin, and Collins orbited the Moon 30 times and observed all manner of craters and other formations, paying particular attention to the region where they planned to land, the Sea of Tranquillity. Previous unmanned spacecraft had imaged the area, and it appeared to be a safe landing site because of its flat terrain. The exact position was about 12 miles (19 km) southwest of the crater Sabine D, a 1.5-mile-diameter (2.4 km), dish-shaped welt on the lunar surface that later would be renamed Collins in honor of the command module pilot.
Stick the landing
On July 20, operations commenced that would lead to humanity’s first steps on another world. Collins stayed aboard Columbia as Armstrong and Aldrin climbed aboard Eagle and began a descent operation. As the two craft separated, Collins carefully viewed Eagle for any possible signs of physical damage as the lunar lander turned in front of him.
Standing inside the cramped LM, Armstrong and Aldrin frantically checked readings and looked through the craft’s narrow window. As they recognized landmarks, they realized they were seeing them about four seconds ahead of the planned exercise — they were going “long,” and the spacecraft would pass the intended landing site.
As they slowly descended and approached an altitude of about 6,000 feet, two program alarms sounded: The spacecraft computer recognized that it could not accomplish all the checks it should in real time. At Mission Control in Houston, engineers were not overly concerned, and they allowed the descent to continue. Later, NASA computer programming chief Margaret Hamilton wrote that the overload occurred due to a checklist error for the spacecraft preparation, and that the computer automatically ignored lower-priority tasks in order to focus on the descent.