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Space exploration
Apollo: Mission to the moon

 

Human beings enter space

The race to the moon dominated the space race of the 1960's. In a 1961 address to Congress, President John F. Kennedy called for the United States to commit itself to "landing a man on the moon and returning him safely to Earth" before the 1960's ended. This goal was intended to show the superiority of U.S. science, engineering, management, and political leadership.

NASA considered several proposals for a piloted lunar mission. The agency selected a plan known as lunar-orbit rendezvous. A spacecraft would carry three astronauts to an orbit around the moon. Two of the astronauts would then descend to the lunar surface.

The spacecraft would consist of three parts, or modules-a command module (CM), a service module (SM), and a lunar module (LM), which was originally called the lunar excursion module (LEM). The cone-shaped CM would be the spacecraft's main control center. The SM would contain fuel, oxygen, water, and the spacecraft's electric power system and propulsion system. The CM and SM would be joined for almost the entire mission as the command/service module (CSM).

Only the LM would land on the moon. This module would consist of two sections-a descent stage and an ascent stage. The two stages would descend to the lunar surface as a single unit, but only the ascent stage would leave the moon.

apollo spacecraft

A Saturn 5 booster would launch the spacecraft toward the moon. As the craft approached the moon, rockets on the SM would adjust its course so that it would go into a lunar orbit. With the craft in orbit, the LM would separate from the CSM and carry the two astronauts to the surface. After the astronauts completed their activities on the moon, the LM's ascent stage would blast off from the descent stage and rendezvous with the CSM.

After the returning astronauts entered the command module, the CSM would cast off the LM's ascent stage. The CSM would then return to Earth. As the craft approached Earth, the CM would separate from the SM and would splash down in the ocean.

Lunar-orbit rendezvous would be complex but relatively economical. The mission would save a tremendous amount of fuel by landing only the small LM on the moon and then launching only its ascent stage.

Making ready. Tragedy struck during preparations for the first piloted Apollo flight, a trial run in low earth orbit. During a ground test on Jan. 27, 1967, a flash fire inside the sealed CM killed astronauts Grissom, White, and Roger B. Chaffee. An electrical short circuit probably started the fire, and the pure oxygen atmosphere caused it to burn fiercely.

A few months later, the Soviet space program also suffered a disaster. The Soyuz (Union) 1 capsule was launched with Vladimir Komarov aboard as pilot. It was supposed to link up with a second piloted spaceship, but Soyuz 1 developed problems and the second ship was never launched. Controllers ordered Soyuz 1 to return to Earth. But a parachute failure caused the capsule to crash, killing Komarov.

While the Apollo CSM and the Soyuz capsule were being redesigned, unpiloted tests took place as planned. The United States launched the first Saturn 5 booster on Nov. 9, 1967, with complete success. Early in 1968, an LM was sent into orbit, where it test-fired its engines. Soyuz vehicles linked up automatically in orbit in 1967 and 1968.

Orbiting the moon.
By late 1968, the United States had redesigned the Apollo CSM. However, the lunar module remained far behind schedule.

NASA officials knew about Soviet preparations for a piloted lunar fly-by. To beat the Soviets, NASA decided to fly a piloted mission to orbit the moon, without an LM. The orbital mission would also test navigation and communication around the moon.

Apollo 8, the first piloted expedition to the moon, blasted off from the Kennedy Space Center near Cape Canaveral, Florida, on Dec. 21, 1968. Hundreds of thousands of people crowded nearby beaches to watch the launch. The spacecraft carried astronauts Borman, Lovell, and William A. Anders. After three days, the crew fired the SM engine to change course into a lunar orbit. They made observations and took photographs, then headed back to Earth. Apollo 8 landed safely in the Pacific Ocean near Hawaii on December 27.

Two additional test flights were made to ensure the safety and effectiveness of the lunar module. The LM was tested in low orbit around Earth by the Apollo 9 astronauts and in lunar orbit by the Apollo 10 crew.

Landing on the moon. Apollo 11 was the first mission to land astronauts on the moon. It blasted off on July 16, 1969, carrying three astronauts-Neil A. Armstrong, Buzz Aldrin, and Michael Collins.

The first two stages of a Saturn 5 rocket carried the spacecraft to an altitude of 115 miles (185 kilometers) and a speed of 15,400 miles (24,800 kilometers) per hour, just short of orbital velocity. The third stage fired briefly to accelerate the vehicle to the required speed. It then shut down while the vehicle coasted in orbit. The astronauts checked the spacecraft and lined up the flight path for the trip to the moon. The third stage was then restarted, increasing the speed to an escape velocity of 24,300 miles (39,100 kilometers) per hour. On the way to the moon, the crew pulled the CSM away from the Saturn rocket. They turned the CSM around and docked it to the LM, which was still attached to the Saturn. The linked vehicles then pulled free of the Saturn.

For three days, Apollo 11 coasted toward the moon. As the spaceship traveled farther from Earth, the pull of Earth's gravity became weaker. But Earth's gravity constantly tugged at the spacecraft, slowing it down. By the time the ship was 215,000 miles (346,000 kilometers) from Earth, its speed had dropped to 2,000 miles (3,200 kilometers) per hour. But then the moon's gravity became stronger than Earth's, and the craft picked up speed again.

Apollo 11 was aimed to pass directly behind the moon. However, it was moving much too fast for the moon's weak gravity to capture it. A braking rocket burn changed its course into a low lunar orbit.

Once in lunar orbit, Armstrong and Aldrin separated the LM from the CSM. They fired the LM's descent stage and began the landing maneuver. They used the LM's rockets to slow its descent. Collins remained in the CSM.

To help NASA mission controllers recognize voice signals from the CSM and the LM, the astronauts used different call signs for the two vehicles. They called the CSM Columbia and the LM Eagle.

The LM's computer controlled all landing maneuvers, but the pilot could override the computer if something unexpected occurred. For the final touchdown, Armstrong looked out the window and selected a level landing site. Probes extended down from the LM's landing legs and signaled when the LM was about 5 feet (1.5 meters) above the surface. The engine shut off, and the LM touched down at a lowland called the Sea of Tranquility on July 20, 1969. Aldrin radioed a brief report on the vehicle's status. Moments later, Armstrong radioed back his famous announcement: "Houston, Tranquility Base here. The Eagle has landed."


Contributor: James Oberg, M.S., Spaceflight Engineer; author, UFOs and Outer Space Mysteries.
Source : World Book 2005

Space exploration
 
What is space?
Getting into space and back
Living in space
Microgravity
Meeting basic needs in space
Communicating with Earth
The dawn of the space age
Space probes
Probes to Venus
Probes to Jupiter and beyond
Probes to comets
Human beings enter space
Apollo: Mission to the moon
Exploring the moon
Returning to Earth
The International Space Station
Space shuttles
Types of shuttle missions