On July 20, 1969, television sets around the world broadcast the same grainy image: Neil Armstrong climbing down the ladder of the Eagle Lunar Landing Module and touching his boot to the surface of the moon. His words, "That's one small step for man; one giant leap for mankind," became forever ingrained in the human consciousness. The famous landing was a triumphant end to the space race.
But that historic moment on the surface of the moon was the result of many years' efforts by both the Soviet and American space programs. The astronauts who first touched the moon's surface had to travel some 238,000 miles (383,000 kilometers) to reach their destination, survive the moon's harsh environment and make it back to Earth in one piece. It was no easy feat.
As of today, only 12 people -- all of them men and all of them part of the American space program -- have walked on the moon. The exclusivity of the elite group might soon change, however. NASA, other nations' space programs and several private space entrepreneurs are planning more missions that could send humans back to the moon within a few years.
In this article, we'll look at the history of lunar exploration, learn about the technology that got us to our nearest celestial neighbor and find out if humans might soon be returning to -- and even one day living on -- the moon.
In the 1950s, the United States was locked in a race with the Soviet Union for dominance in space. The competition grew out of the Cold War. On Jan. 2, 1959, the Soviet Luna 1 spacecraft made the first lunar flyby at a distance of 3,725 miles (5,994 kilometers) from the moon's surface. The Russians were also the first to impact the moon on Sept. 12, 1959, with the second Luna mission.
But on May 25, 1961, President John F. Kennedy issued a challenge in his speech to Congress: "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to Earth" [source: NASA]. American astronauts accepted the challenge, and on March 3, 1959, the Pioneer 4 probe became the first American spacecraft to fly by the moon.
The U.S. Ranger program, which ran from 1961 to 1965, sent nine missions to the moon. In 1962, Ranger 4 reached the lunar surface but was unable to send back any data before it crashed. Two years later, Ranger 7 captured and sent back more than 4,000 photos before it hit the surface of the moon.
The next step in the race to the moon was to land a craft gently without crashing. The Soviets beat the Americans, touching down the Luna 9 on Feb. 3, 1966. However, the Americans weren't far behind. The Surveyor 1 mission made a controlled landing on the moon about three months later.
All of these steps in lunar exploration were leading up to the ultimate goal: landing a manned spacecraft on the moon. However, tragedy struck during a preflight test on Jan. 27, 1967, when a fire swept through the Apollo Command Module, killing astronauts Roger Chaffee, Virgil "Gus" Grissom and Edward White. NASA named the test Apollo 1 to honor the crew. Because of the fire, NASA put its lunar launchings on hold for a year while it redesigned the module.
The delay wasn't the only difficulty facing astronauts. In order to successfully execute a manned lunar landing, scientists had to get the spacecraft out of Earth's gravity, put it into orbit around the moon, land without crashing and return through the Earth's atmosphere without burning up.
And so NASA launched Apollo 7 into space on Oct. 11, 1968. The crew, made up of astronauts Walter M. Schirra Jr., Donn F. Eisele and Walter Cunningham, orbited Earth 163 times and spent nearly 11 days in space.
The Apollo 8 mission launched on Dec. 21, 1968. It was the first crewed mission to use the Saturn V rocket, which was powerful enough to take the spacecraft into lunar orbit. The crew of Frank Borman, James A. Lovell Jr. and William A. Anders circled the moon and successfully returned into Earth's atmosphere.
On March 3, 1969, the Apollo 9 mission launched. James A. McDivitt, David R. Scott and Russell Schweickart orbited Earth 152 times and practiced docking procedures between the Command Module (which would house the astronauts in space) and the Lunar Module (which would make the moon landing). They had to perfect these procedures before attempting an actual landing.
The final stage in the dress rehearsal came on May 18, 1969, with the launch of Apollo 10. It involved every step of a lunar landing -- except for an actual landing. Commander Thomas Stafford and Lunar Module pilot Eugene Cernan lowered the Lunar Module to within 50,000 feet (15,240 meters) of the moon's surface, while John W. Young remained in the Command Module in lunar orbit.
In the next section, we'll learn about the first moon landing.
Was the Apollo 11 Moon Landing a Hoax?
Some skeptics still believe that the Apollo 11 lunar landing was simply a movie studio hoax staged by NASA. In 2001, the Fox television network aired a program that gave the hoax theory second wind.
Guests on the show suggested that NASA didn't have the technology to pull off a lunar landing in the late 1960s. They noted that the pictures of astronauts sent back from the moon didn't show stars in the sky. A NASA expert refuted this by explaining that the stars wouldn't have shown up on film because the foreground image (the astronauts' space suits) was so bright.
People who are still unconvinced by the overwhelming evidence of man's landing on the moon can visit the National Air and Space Museum in Washington, D.C., where samples of rocks taken from the moon's surface are on display.
The Apollo 11 Mission
Previous missions had flown by the moon, landed on it and sent back photographs of its surface. But by July 1969, NASA was ready to land men on the moon. The historic mission's crew was made up of Commander Neil Armstrong, Command Module Pilot Michael Collins and Lunar Module Pilot Edwin "Buzz" Aldrin.
This is how the mission unfolded:
July 16, 1969 at 9:32 a.m. EDT -- A Saturn V rocket carrying the Apollo 11 spacecraft lifted off from John F. Kennedy Space Center in Florida. It carried the Command Service Module housing the astronauts and a Lunar Module that Armstrong and Aldrin would use to land on the moon. After orbiting the Earth one-and-a-half times, the Saturn V's third stage re-fired and sent Apollo 11 rocketing toward the moon. Soon after, the Command Service Module, Columbia, separated from the Saturn, flipped around and connected nose-to-nose with the Lunar Module, Eagle. The joined spacecraft continued on its path.
July 19 -- Apollo 11 entered lunar orbit. After 24 hours in orbit and a check of the Lunar Module's switches and communication systems, Armstrong and Aldrin separated Eagle from Columbia and prepared to make their descent to the moon's surface. Collins remained in Columbia to serve as the communication link between the Lunar Module and mission control back on Earth.
July 20 -- 102 hours after launch, at 4:17 p.m. EDT, Armstrong and Aldrin landed in the Sea of Tranquility, a flat lava plain on the moon's surface. Armstrong sent this famous message to mission control: "Houston. Tranquility Base here. The Eagle has landed." Just moments after landing, the two astronauts began preparing to abort their mission immediately and return to the Command Service Module, just in case an emergency occurred. Then they powered down.
Six-and-a-half hours later, Armstrong stepped out of the spacecraft and took his first steps on the moon.
Once Aldrin joined Armstrong on the moon's surface, the pair of astronauts began collecting lunar surface material. As they worked, they noted the differences in the moon's gravity compared to Earth. Because the moon has one-sixth of Earth's gravity, the astronauts had to move by slowly loping or hopping with both feet like a kangaroo.
While on the moon, Armstrong and Aldrin created a now-famous image as they erected the American flag. This wasn't as easy as it looked. The pole went in the first 5 to 6 inches (12.7 to 15.2 centimeters) of lunar soil easily but then met with resistance. The astronauts had to lean the flag back slightly to get it to stay in the ground.
While on the moon, the two astronauts collected nearly 50 pounds (23 kilograms) of lunar material, took photos of the area near the landing site, set up equipment and pulled two core-tube samples from the moon's surface. They left behind a disc with 73 messages from countries around the world, a patch from Apollo 1, medals from Russian cosmonauts and a symbol of the U.S. eagle carrying an olive branch.
July 21-- 21 hours after their arrival, at 1:54 p.m. EDT, Armstrong and Aldrin lifted off from the moon, leaving the lower stage behind. Inside the Lunar Module, they traveled back into the moon's orbit, where they docked with the Command Service Module. The Eagle was set free.
July 24 -- Apollo 11 entered the Earth's atmosphere at a speed of 36,194 feet (11,032 meters) per second. It landed in the Pacific Ocean at 12:51 p.m.
In the next section, we'll look at profiles of the lunar landing missions.
Profiles of the Lunar Landing Missions
Lunar spacecraft were made up of two parts. The Command and Service Module carried the crew, operations systems, oxygen, water, fuel and propulsion system. The Lunar Module carried the astronauts to the moon.
These modules were attached to a Saturn V rocket. Powered by liquid hydrogen and as tall as a 36-story building, the Saturn V was made up of three stages. The first stage boosted the rocket through the first 38 miles (61 kilometers) of ascent. The second stage sped the rocket through the upper atmosphere and into the Earth's orbit. The third stage propelled the craft to the moon.
Once under way, the crew separated the Command and Service Module from the third stage and fired its engine. They released the third stage and sped toward the moon. They then turned the module around and docked it nose-to-nose with the Lunar Module.
Once in lunar orbit, the Lunar Module separated from the Command and Service Module and moved in for a moon landing with two astronauts inside. The remaining astronaut stayed behind in the Command and Service Module, orbiting the moon.
The astronauts in the Lunar Module put the engine into full throttle to begin their descent to the moon. More than a dozen small thrust motors helped control the direction and speed of the descent to land the module gently. Because the moon has no atmosphere, the crew members couldn't calculate their altitude and airspeed. The Lunar Module sent out microwave beams to the moon's surface to provide information on the spacecraft's position.
At just a few thousand feet above the moon's surface, a computer onboard the spacecraft initiated the approach phase. The computer needed to adjust both horizontal and vertical speeds to almost zero, while the crew had to adjust for craters and other formations on the moon's surface to avoid crashing.
The Lunar Module commander had the choice of whether to land automatically using the craft's computers, or manually, depending on how clear the landing site was. The pilot had learned how to steer the craft into a landing during simulations on Earth. When the Lunar Module landed, the commander hit the engine-stop button. The craft went into zero-gravity for a second and then the rocket engines on its bottom platform lowered it to the moon's surface.
When the mission was completed, the Lunar Module fired its ascent engine to escape the moon's gravitational pull and lifted off. Because the moon's gravity is lower than that of Earth, the spacecraft had to travel 1.4 miles (2.3 kilometers) per second to escape the moon's atmosphere, compared to the 7 miles per second, or almost 25,000 miles per hour, (11 or 40,233 kilometers, respectively) it had to travel to escape the Earth's atmosphere on the way up.
The Lunar Module docked with the Command and Service module. The two astronauts who had made the landing moved from the Lunar Module to the Command and Service Module with their equipment, and any samples they collected from the moon. They then closed the hatch and released the Lunar Module, sending it crashing back to the moon.
The next challenge was to re-enter Earth's atmosphere without burning up like a meteor. To avoid this, the module was coated in an ablative covering that burned away as it entered Earth's atmosphere and protected the spacecraft underneath from the intense heat.
In the next section, we'll learn about subsequent trips to the moon.
Returning to the Moon
Apollo 11 was the first U.S. mission to land on the moon, but it wasn't the last. Here are rundowns of the other six moon missions:
Launch date: Nov. 14, 1969
Crew: Charles Conrad Jr. (Commander), Richard F. Gordon (Command Module Pilot), Alan L. Bean (Lunar Module Pilot)
Landing site: Sea of Storms
Mission: recovered pieces from the Surveyor 3 to help scientists study the effects of time on equipment in the moon's environment and proved precise lunar landings were possible.
Launch date: April 11, 1970
Crew: James A. Lovell, Jr. (Commander), John L. Swigert Jr. (Command Module Pilot), Fred W. Haise Jr. (Lunar Module Pilot)
Mission: The crew aborted after an oxygen tank in the Service Module exploded and ruptured mid-flight. The crew moved into the Lunar Module and safely navigated back to Earth.
Launch date: Jan. 31, 1971
Crew: Alan B. Shepard Jr. (Commander), Stuart A. Roosa (Command Module Pilot), Edgar D. Mitchell (Lunar Module Pilot)
Landing site: Fra Mauro region
Mission: Shepard and Mitchell climbed the side of Cone Crater to see how easily they could move in their bulky space suits. Shepard hit two golf balls.
Launch date: July 26, 1971
Crew: David R. Scott (Commander), Alfred J. Worden (Command Module Pilot), James B. Irwin (Lunar Module Pilot)
Landing site: Hadley Rille/Apennines region
Mission: Astronauts used the Lunar Roving Vehicle to explore the surface of the moon. Scott demonstrated that a hammer and feather fell at the same rate. The crew left behind a plaque commemorating the 14 American and Soviet astronauts who had died since the space program's start.
Launch date: April 16, 1972
Crew: John W. Young (Commander), Thomas K. Mattingly II (Command Module Pilot), Charles M. Duke Jr. (Lunar Module Pilot)
Landing site: Descartes region
Mission: Covered nearly 17 miles in the Lunar Roving Vehicle. The crew collected rock and soil samples and used an ultraviolet camera and spectrograph to capture the first astronomical measurements from the moon's surface.
Launch date: Dec. 7, 1972
Crew: Eugene A. Cernan (Commander), Ronald E. Evans (Command Module Pilot), Harrison H. Schmitt (Lunar Module Pilot and scientist)
Landing site: Taurus-Littrow region
Mission: Covered more than 60 miles (97 kilometers) in the Lunar Roving Vehicle and studied volcanic vents to learn about the moon's origins. The crew left a plaque reading, "Here man completed his first exploration of the moon, December 1972 A.D. May the spirit of peace in which he came be reflected in the lives of all mankind."
Before taking his final step off of the moon, Gene Cernan uttered the last words to be spoken on its surface: "We leave as we came and, God willing, as we shall return, with peace and hope for all mankind."
After six moon landings, American scientists had a greater understanding of our nearest celestial neighbor. They determined the age of the moon -- about 4.5 billion years -- and came up with a theory for how it formed.
After the Apollo program ended in 1972, NASA did not send any more astronauts to the moon. With the country mired down in the Vietnam War, the once enraptured public was beginning to lose interest in the space missions. In the next section, we'll learn about the future of lunar exploration.
What We Left Behind
The Apollo missions left six American flags on the moon -- one for each landing. Scientists believe they are still there, although they're not sure whether the flags are standing.
The Future of Lunar Exploration
The moon has remained untouched by humans for more than four decades. In 2004, President George W. Bush vowed to send astronauts to the moon by 2020, but the Constellation program lost its funding, and the space shuttles were retired.
Thankfully though, it's no longer just governments involved in the space race -- a number of wealthy entrepreneurs also want their shot at glory. Google has offered up a $25 million prize to the first person who can send an unmanned spacecraft to the moon. To win the Google Lunar X Prize, entrants must not only land a craft on the moon but also travel 1,640 feet (500 meters) in a lunar rover and send back high-resolution video and photos from the surface of the moon.
At least one company is planning to sell trips to the moon to wealthy would-be astronauts. Space Adventures offers tourists trips aboard a modified Russian Soyuz spacecraft. The trip, which also includes a stay at the International Space Station, can be had for a mere $100 million.
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To get ready for the next trip to the moon, NASA scientists have simulated the harsh lunar environment in the most unforgiving place on Earth -- Antarctica. They've tested out housing units that look like high-tech versions of carnival moonwalks. Each inflatable unit provides 384 square feet (36 square meters) of insulated, heated and pressurized living space. Tests will show how well these structures might hold up on the moon.
In NASA's Marshall Space Flight Center in Huntsville, Ala., scientists have also experimented with grains of moon dust (collected during the Apollo 17 mission) to see how the dust behaves, how it might damage sensitive equipment and find out if it harms astronauts' lungs.