Space Race

In 1953 NACA began developing the world's first spaceship. The goal of NACA's program was to develop an aircraft that could explore the problems of upper-atmospheric and near-space flight. For instance, how would the pilot control the craft? What would the pilot's physical reactions be to flying at such great altitudes? The flights would be done at speeds of Mach 6.6 and higher and at altitudes of 12 to 50 miles (19 to 80 km). The result of NACA's program was the development of the X-15, one of the most successful research rocket planes ever flown.

The X-15 was a slender, black, 50-foot (15 m) rocket plane. It had stubby, knife-edged wings and control surfaces for atmospheric flight, like those on ordinary planes. But there would be too little air to use normal wing and tail controls at the highest altitude it was expected to reach. Therefore, the X-15 also had nose and wingtip thrusters so it could be maneuvered in the fringes of space. (The X-15's resemblance to the Sänger Silver Bird was no accident. The German team's research had a huge influence on the X-15's designers.)

The X-15 was so similar to a spaceship that its pilot was required to wear a full-pressure space suit. In fact, many X-15 pilots were given astronaut status since the maximum altitude reached by the plane was more than 67 miles (108 km). This altitude was well beyond the official threshold of space. At one point, NACA scientists considered mounting an X-15 on top of a large booster rocket and launching it into Earth orbit. Of the three X-15s built, two had long service lives. They made a total of 199 successful flights. In the process, they provided enormous quantities of data vital to the fledgling U.S. space program.

After losing World War II, Germany lost some of its top rocket scientists to the United States. Chief among these was Wernher von Braun, who had been in charge of the V-2 project. Von Braun was an engineering genius who probably knew as much or more about rockets than any other person at the time. He was also a great visionary who had always kept his eyes on one major goal: the development of space travel.

Von Braun was a compelling speaker who easily conveyed his enthusiasm for space travel. He was also a skilled writer who had a talent for explaining technical details in terms anyone could understand. Through appearances on television and a long series of influential illustrated magazine articles, von Braun began to convince the American people that space travel was not a fantasy. Much as Jules Verne had done a century earlier, he demonstrated that it could be accomplished by means of existing technology. The only thing missing was the commitment.

As a result, more and more pressure was put upon the U.S. Congress to fund a full-scale space program. But the government still dragged its feet. That is, until October 4, 1957. On that day, the Soviet Union placed the first artificial satellite, Sputnik 1, into orbit around Earth.

U.S. politicians were stunned by this news, although they shouldn't have been. Many scientists had been trying to warn the government that the Soviets were on the verge of spaceflight. But the United States was still basking in the glow of its victory in World War II. U.S. leaders were convinced that only the United States had even a marginal chance of launching a spacecraft into orbit. To make things worse, the Soviet Union was a dictatorship and an enemy. U.S. leaders had been telling citizens that such a nation just wasn't capable of achieving anything before a free democratic country.

The United States immediately started a program to get a satellite into orbit as soon as possible. A satellite launcher called Vanguard had many embarrassing failures. (Unlike the Soviet Union, which publicized only its successes, the United States televised its launches-and failed launches-for the whole world to see.) After the Vanguard's failures, von Braun received approval to do what he had wanted to do all along. He could assemble a satellite launcher from the existing, well-proven rockets he had been helping the army develop. In the meantime, Russia launched a second satellite, Sputnik 2. This satellite carried a dog named Laika into orbit.

Finally, on January 31, 1958, the United States launched its first artificial satellite, Explorer 1, into orbit. At 31 pounds (14 kg), it was tiny compared to the Soviet satellites. Sputnik 1 weighed 184 pounds (83 kg), and Sputnik 2 weighed 1,120 pounds (508 kg). Even so, Explorer 1 was a source of immense national pride and relief. But the United States' joy was short lived.

On April 12, 1961, the Soviet Union launched the first human being into space. He was a young pilot named Yuri Gagarin. Gagarin made one circuit of Earth in his Vostok (East) capsule. The Soviets cheered and gloated while the Americans swore that they would never again be upstaged. The rivals began a full-scale space race.

In 1958, a year after the success of the first Soviet satellite, U.S. president Dwight Eisenhower signed an act creating NASA. It had the task of developing a civilian space program.

In December of that same year, NASA announced that its official manned space program would be called Project Mercury. The project had two goals. First, it was to investigate the ability of humans to survive and work in the environment of space. Second, it was to develop and test the basic hardware for future manned spaceflight programs.

In 1961 President John F. Kennedy told Congress, "I believe 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." Kennedy's announcement spurred the nation to create a systematic, step-by-step program that would end with a lunar landing. Project Mercury became the opening act for the new lunar landing program, which was to be called Apollo.

For all the scientific and human value of manned spaceflight programs, the decision to go to the Moon was basically a political one. The United States had been nursing the bruises it had received from the Soviet Union's unexpected advances in space. Evidence existed that the Soviets were gearing up for a lunar landing mission. The Americans simply would not let them get there first.

The United States underwent a great deal of international criticism about the slow, methodical pace at which it was undertaking its manned space program. But it turned out that it had taken the right course. Decades after the first manned spaceflights, U.S. scientists learned that the Soviets had taken many shortcuts in their haste to get a man into orbit as soon as possible. Some of these shortcuts had proven fatal. At least four cosmonauts (Soviet astronauts) died during the reentry of their spacecraft from orbit. The intense secrecy of the Soviet government, which controlled the news with an iron fist, kept these tragic failures from becoming widely known to Soviet citizens and the rest of the world. By contrast, between the start of the Mercury program and the Challenger space shuttle disaster on January 28, 1986, three U.S. astronauts were killed.

The Mercury capsule, the United States' first manned spacecraft, was barely large enough to contain the single astronaut it carried. It was a cone only 6.2 feet (1.9 m) at its widest point. It had a curved heat shield at its base-which would prevent the capsule from burning up on reentry-and a kind of tower on top.

At the top of the tower was a solid fuel rocket motor with three nozzles. This motor was designed to carry the capsule away from its booster in case an emergency occurred at takeoff. Between the base of the tower and the top of the capsule was the cylindrical parachute container. The astronaut could adjust the attitude of the capsule (the angle by which it was oriented to Earth) by using small thrusters located on the sides and top of the capsule.

Beneath the heat shield was a cylindrical retrorocket pack. These rockets slowed down the capsule for reentry from orbit. The pack was thrown away just before reentry to leave the heat shield clear.

Mercury capsules-like all U.S. spacecraft until the space shuttle-were recovered at sea. As the capsule's parachute lowered it near the surface of the water, the heat shield was dumped and a landing bag was deployed from the base of the capsule. This served as a collapsible air cushion to soften the shock of impact. The capsule itself had enough buoyancy to float upright.

The Soviet Union had already beaten the United States in the race to launch a person into space. But less than a month later, on May 5, 1961, NASA launched Alan Shepard Jr. into space aboard the Mercury 3 capsule. Unlike Gagarin's orbital flight, Shepard's was suborbital. Instead of going into orbit, the capsule simply followed a curved path, rising into space and then dropping back toward Earth, like that of a bullet shot from a gun. In August Soviet cosmonaut Gherman Titov spent just over a full day in space, orbiting Earth seventeen times before returning.

On February 20, 1962, the United States finally succeeded in placing a human in orbit. John Glenn Jr. circled Earth three times in his Mercury 6 capsule. Mercury capsules had a retrorocket pack strapped to their large, curved heat shields. These rockets were fired to slow the capsules for their return to Earth. Once the rockets were fired, the packs would be thrown off to leave the heat shield clear for reentering Earth's atmosphere.

But Glenn's ground crew received a signal that the heat shield on his capsule had come loose. If it were to come off during reentry, the capsule would burn up like a meteor from friction with Earth's atmosphere. The ground crew decided to keep the retrorocket pack attached, hoping that its straps would help keep the heat shield in place. No one was sure what would happen during reentry. Would the disintegrating retrorocket pack damage the capsule? Would the pack tear away the heat shield entirely? Fortunately, the plan worked. Even though Glenn reported seeing flaming chunks of the retrorocket pack flying past his window, he made a successful return to Earth.

For the next several years, spaceflight firsts bounced from one nation to the other. On May 24, 1962, U.S. astronaut Scott Carpenter made three orbits of Earth in his Aurora 7 Mercury capsule. Three months later, cosmonaut Andrian Nikolayev made 64 orbits in a mission lasting more than ninety-four hours. More U.S. and Soviet flights were made, each adding more and more orbits. Then, in June 1963, the Soviets placed the first woman, Valentina Tereshkova, into orbit. (NASA had barred women from spaceflight training until 1978. So the United States did notmatch this feat until 1983.)

The Soviets continued to set the bar ever higher for the Americans by launching the first multiple-person crews into orbit. Voskhod 1 carried three cosmonauts in 1964. This was followed soon after by the two-person Voskhod 2, carrying Pavel Belyayev and Alexei Leonov. During their twenty-six hours in orbit, Leonov sealed his space suit, opened a hatch, and left the spacecraft. For ten minutes, he floated in space, attached to the spacecraft only by a 5-foot (1.5 m) tether, making the first space walk in history.

One thing Leonov hadn't counted on, though, was the fact that his space suit would expand in space like a balloon because of the air pressure inside it. When he tried to get back into the spacecraft, he was too big to fit through the hatch. The only solution was to release some of the air in his suit, deflating it enough for him to get through the hatch. Opening his space suit in the vacuum of space must have taken enormous courage since even a few seconds of exposure might have been fatal.

Project Gemini followed NASA's Mercury program. Although the Gemini spacecraft looked like the Mercury spacecraft, it was more technologically advanced, much larger, and carried two astronauts (hence the project name, Gemini-the constellation of the twins). The goal of the program was to test the effects of long-term spaceflight, extravehicular activities (EVAs), orbitalmaneuvering, and rendezvous and docking techniques. These skills would be essential for a future mission to the Moon. The first Gemini flight took place on March 23, 1965, when U.S. astronauts Virgil Grissom and John Young rode Gemini 3 into orbit. Although the mission lasted only four hours, the astronauts still had time to perform several scientific experiments.

During the mission, Young presented Grissom with a corned beef sandwich he had smuggled on board. Astronauts' diets were strictly regulated. More important, food needed to be kept contained within tubes and packets. This prevented crumbs and other debris from potentially getting into the spacecraft's electrical and life-support systems and causing problems. (The spacecraft's air filters were not designed to handle crumbs.) Corned beef sandwiches are messy, and NASA officials were not amused by the stunt.

Eventually, twelve Gemini missions launched before the program was completed in 1966. These missions included the first U.S. space walk and the first-ever use of a device that allowed an astronaut to maneuver while outside the spacecraft. The device was a small, handheld gunlike tool that released jets of compressed gas. For more than twenty minutes, astronaut Ed White flew independently of his Gemini 4 capsule, becoming a spaceship in his own right.

The Gemini spacecraft looked similar to the earlier Mercury capsule. It was much larger, however, and much more sophisticated. Carrying a two-person crew, it consisted of two main components: the cone-shaped spacecraft and a large equipment module attached to its base.

The equipment module contained all the electronic equipment, as well as fuel cells for generating power. It also held life support that could withstand the vacuum of space and didn't need to be contained in the capsule itself. (This gave the astronauts much more room.) The life support system not only provided the astronauts with breathable air but removed impurities and maintained the temperature of the spacecraft. The equipment module was discarded before reentry.

The spacecraft itself was 11 feet (3.4 m) long and 7.5 feet (2.3 m) wide at its base. A cylinder at the nose of the capsule contained the recovery parachute, as well as the equipment needed for docking.

Gemini astronauts also practiced rendezvousing (coming together at a specific time and place) with another spacecraft. Orbit rendezvous between two spacecraft was going to be an essential part of the Apollo program, which was still in the planning stages. NASA had decided to use the Lunar Orbit Rendezvous method for its upcoming lunar landing. In this plan, the main spacecraft would act as a kind of "ferry" for the lunar lander.

To practice these techniques, Gemini spacecraft rendezvoused with each other, although the spacecraft were incapable of docking (joining mechanically). On December 4, 1965, Gemini 6 rendezvoused with Gemini 7. The two spacecraft maneuvered so closely that the astronauts in each spacecraft could wave to one another. During the course of the mission, Gemini 7 also made the longest spaceflight up to that time: more than 330 hours.

The Gemini 8 astronauts were launched into space on March 16, 1966. To practice both rendezvousing and docking, an Atlas multistage rocket had previously boosted an unmanned Agena stage into orbit. The idea was for the astronauts to carefully approach the Agena and briefly dock with it. This proved to be much more difficult than it sounded. At first, the Agena failed to go into orbit. And even after docking successfully, the maneuver still involved a great deal of danger.

After astronauts Neil Armstrong and David Scott rendezvoused and docked Gemini 8 with the Agena stage, the two spacecraft, which were now joined, began rolling wildly. Armstrong detached Gemini 8 from the Agena, but Gemini 8 continued to spin even faster. The hand controls failed, and even NASA's mission control back on Earth didn't know what to do. Finally, the controls started to function again and the astronauts were able to get their spacecraft under control.

The final mission of Project Gemini was Gemini 12, launched on November 11, 1966, with astronauts James Lovell and Edwin "Buzz" Aldrin on board. Again, the spacecraft was preceded into orbit by an Agena. Aldrin practiced working in space using a variety of specially designed space tools while attached to the spacecraft by restraints. During the course of three space walks, he worked outside the capsule for a total of five and a half hours.

Although the Gemini program had many problems, overall it was a great success. The astronauts practiced and perfected many of the techniques required for a mission to the Moon. The next step in the U.S. space program would be the Apollo lunar landings. Unlike Gemini, however, the Apollo program opened with a tragedy.

Less than three months after the successful conclusion of the Gemini program, the first Apollo capsule was sitting atop its titanic Saturn 1B rocket. On January 27, 1967, NASA held a dress rehearsal for the launches that would eventually take place.

Astronauts Ed White, Virgil "Gus" Grissom, and Roger Chaffee were on board the Apollo capsule. They were testing the launch systems when a fire suddenly broke out. Although all the propellants had been removed from the capsule, the pure oxygen atmosphere caused the plastics inside to burn fiercely. Within fifteen seconds, the three men were dead from suffocation. It took ninety seconds for a rescue crew to open the hatch.

The Apollo launch schedule was put on hold for nearly two years. Engineers rethought and redesigned the capsule to make future capsules fireproof. It was not until October 11, 1968, that the first manned Apollo spacecraft, Apollo 7, went into orbit for an eleven-day mission.

To everyone's relief, the mission was a complete success. Astronauts Wally Schirra, Donn Eisele, and Walter Cunningham made 163 orbits of Earth. They demonstrated the ability of the spacecraft and its crew to make long-term space missions, which would be required for a lunar landing.

The next U.S. mission was to the Moon-but not to land. Launched from Earth on December 21, 1968, Apollo 8 went into lunar orbit, circling the Moon ten times before firing its engines for its return to Earth. The crew spent Christmas 70 miles (113 km) above the lunar surface. They celebrated Christmas Eve by taking turns reading from the Bible's book of Genesis.

NASA sent Apollo 9 into orbit on March 3, 1969. It practiced rendezvous and docking maneuvers in Earth orbit. NASA launched Apollo 10 on May 18 of that same year. It was a full dress rehearsal for the lunar landing. Astronauts Thomas Stafford and Eugene Cernan piloted the lunar module (the spacecraft designed to land on the moon) to within 50,000 feet (15,240 m) of the lunar surface before returning to the command module (the main spacecraft). NASA declared that it was ready to make the first landing on the Moon.

The Apollo spacecraft consisted of two parts: the command module and the service module. The command module was a large, squat cone nearly 11 feet (3.2 m) tall and 13 feet (3.9 m) in diameter. With its three astronauts, it weighed 13,090 pounds (5,937 kg). At the top of the cone was a docking probe that allowed the command module to join with the lunar module, which would ride to the Moon attached to the nose of the command module. A hatch allowed the astronauts to pass from one to the other. The service module contained the electrical power and life-support systems. It also held the propellant tanks and engine needed for boosting the spacecraft from Earth's orbit to lunar orbit and back again.

The three-stage Saturn V rocket was the largest, most powerful rocket ever built. When it was launched for the first time on November 5, 1967, it was as though a volcano had erupted in the middle of the Florida coast. In fact, its sound was compared to the volcano Krakatoa, whose 1883 explosion was the most powerful ever recorded. During launch, the roof of the nearby CBS television building collapsed. And the pressure waves generated by the five huge first-stage engines were detected more than 1,000 miles (1,609 km) away. Each of these engines produced 1.5 million pounds (1 million kg) of thrust. (Compare this to the 60,000 pounds (27,215 kg) of thrust created by the engine of the V-2 and the 20 pounds (9 kg) of thrust created by Goddard's first liquid-fuel rocket.)

The Saturn V was the direct descendant of the V-2 rocket of World War II. It was developed from Wernher von Braun's Redstone rocket. The Saturn V was enormous, standing 363 feet (111 m) high and weighing, at takeoff, 6,423,000 pounds (2,913,500 kg). Everything about the rocket was big. The five F-1 engines in the first stage produced about 7,650,000 pounds (3,470,000 kg) of thrust. It sucked about 3 tons (3 metric tons) of fuel and oxidizer every second from their massive tanks. This was forty times the power of the rocket that had launched Alan Shepard into space.

The first stage took the rocket to an altitude of 42 miles (68 km) in just two and a half minutes, reaching a speed of Mach 9. Then the second stage ignited, building on this speed to reach Mach 22-15,000 miles (24,140 km) per hour-and an altitude of 117 miles (188 km). The third and final stage then took over, putting the Apollo spacecraft into Earth's orbit.

The lunar module, which was used for the actual landing on the Moon, was a strange-looking vehicle that was compared to an insect or wind-up toy. One of the reasons for its odd shape is that it didn't need to be sleek in order to reduce resistance to motion. It would operate only in the airless vacuum of space, where air resistance wasn't an issue.

The lunar module was nearly 23 feet (6.9 m) tall and weighed 33,205 pounds (15,061 kg). Measured diagonally from one landing pad to another, the lunar module was 31 feet (9 m) wide. At the top of the spacecraft was the docking hatch that allowed it to join with the command module. A small door in the side held the ladder that the astronauts used to climb down to the surface of the Moon.

The two astronauts rode standing up. They piloted the lander with much the same skills they would have used flying a helicopter. The astronauts rode in the ascent stage, which also contained the fuel and engine needed for leaving the Moon. Beneath the ascent stage was the large boxlike descent stage. The descent stage contained the fuel and engine necessary for landing on the Moon, as well as four landing legs with their pad-like feet. When it came time to leave the Moon, the ascent stage used the descent stage as its launching pad.

On July 16, 1969, one of the monster Saturn V rockets lofted three astronauts-Michael Collins, Buzz Aldrin, and Neil Armstrong-toward the Moon. After three orbits around Earth, the third and final stage of the Saturn rocket reignited. It accelerated the Apollo 11 spacecraft out of Earth's orbit and toward the Moon at a speed of more than 24,000 miles (38,624 km) per hour. Once the spacecraft was on its way, the third stage was discarded. The astronauts then began their first docking maneuver. The lunar lander, called Eagle, had been stored in a "garage" below the command and service modules. The astronauts had to maneuver it around so that it was attached to the docking hatch at the top of the command module. Four days later, Apollo 11 was in orbit 69 miles (111 km) above the Moon. The astronauts had to begin the delicate operation of detaching Eagle from the command module and getting it ready for its descent to the lunar surface. Aldrin and Armstrong would make the landing while Collins remained in orbit in the command module. Collins pressed a switch, and the two spacecraft gently parted. "See you later," he said to the departing astronauts.

Eagle slowly pivoted until its engine faced forward in the direction the lander was traveling. When fired, the engine acted as a retrorocket, slowing down the spacecraft. Armstrong started the engine, and the lander began to lose speed. As it did, its orbit spiraled down toward the Moon. At an altitude of 7,200 feet (2,195 m), Eagle swung around until its engine pointed down. The lander kept falling until it was just 300 feet (91 m) above the surface of the Moon and traveling only 30 miles (48 km) per hour.

The planned landing site was a broad, smooth plain called the Sea of Tranquility (which is not actually a sea). It was chosen because it looked like a safe place: flat and not many craters. Scientists had gathered this information about the surface of the landing site from photos taken by Lunar Orbiter satellites. No one knew what the surface of the Sea of Tranquility looked like up close. It would not take a very big rock or crater to upset the lander. And very small rocks and craters were too small to be seen clearly in the Orbiter photos. Looking out the window, Armstrong saw that the landing computer was bringing them down onto a field of boulders. The lander would tip over if it set down on any of them. He quickly switched off the computer and took over control manually. He skimmed over the boulders, with almost no fuel left for landing. But he still could not find a safe spot to land. Finally, miles beyond the designated landing area, Armstrong spotted a flat area. With only thirty seconds of fuel left, he began the final descent.

Dust whipped past the windows as the blast from the engine hit the lunar surface. The astronauts could see nothing below them. Three of the landing pads had long antennalike feelers protruding from them. When they contacted the ground, a signal lit up in the cockpit: LUNAR CONTACT. A moment later, all four pads were touching the ground. "Houston," reported Armstrong over the radio, "Tranquility Base here. The Eagle has landed."

Six more Apollo missions to the Moon followed, though only five made it that far. In November 1969, Apollo 12 landed astronauts Pete Conrad and Alan Bean on the Ocean of Storms (which is not actually an ocean), 1,000 miles (1,609 km) from Tranquility Base. One of the highlights of this mission was the astronauts' visit to the Surveyor 3. This was an unmanned lunar probe, which had landed in April 1967. Conrad and Bean collected Surveyor's camera and other parts so they could be returned to Earth for study. They also gathered 74 pounds (34 kg) of lunar rock samples.

For safety's sake, the first two lunar missions had landed on relatively smooth areas called maria (Latin for "seas"), which are flat, waterless lava plains. Apollo 14 was launched on January 31, 1971. It was to explore the highlands of Fra Mauro, a mission it had inherited from Apollo 13. The area was on the edge of Mare Imbrium, a vast plain of lava created millions of years ago when a huge asteroid punched through the lunar crust. An electrical flaw canceled this plan. The terrain of Fra Mauro was very different from the nearly featureless regions Apollo 11 and Apollo 12 had explored. The moonwalkers, Alan Shepard and Ed Mitchell, discovered that they were having a hard time finding their way around on the surface. Much of the problem was due to Shepard's lack of interest in learning about the area before he left Earth. Although he didn't gather much scientific data or samples, Shepard did pull a memorable stunt. He had brought along a golf ball, and using a specially made golf club, he sent the ball sailing "Miles and miles and miles!" he said. (The golf club is on display at the Smithsonian National Air and Space Museum in Washington, D.C.)

The following mission, Apollo 15, was launched on April 16, 1972, and it was much more successful. It explored one of the mysterious lunar rilles (riverlike channels that crisscross the lunar surface). Scientists knew the rilles hadn't been created by flowing water. They were the wrong shape for that. So the scientists wanted to figure out what had caused them.

NASA chose Hadley Rille as the best site to explore. It is at the edge of the towering, 14,000-foot (4,267 m) Hadley Mountains. The area also has a large number of interesting craters that might have volcanic origins. Scientists hoped the mission would return with a rich harvest that would help make up for the disappointment of Apollo 14. Apollo 15 astronauts David Scott and Jim Irwin brought along a sophisticated piece of equipment: a Lunar Roving Vehicle (LRV). The LRV was an electrically powered car that resembled a dune buggy. It allowed the astronauts to travel much farther and carry more equipment than any previous lunar explorers.

Built mostly of lightweight aluminum, the LRV was powered by electric motors and batteries. Its tires were basketlike wheels woven from coated piano wire. It had a maximum speed of 8.7 miles (14 km) per hour. The 1,600-pound (726 kg) LRV was equipped with radio antennas,
television and still cameras, storage compartments for samples, and controls for the astronauts.

Astronauts Scott and Irwin spent three days on the Moon. For twenty-two hours and thirty-six minutes, they were outside the spacecraft exploring Hadley Rille and the area around it. One of their most important discoveries was a small white rock found on the slopes of Mount Hadley. It was a fragment of the earliest lunar crust-at least 4.5 billion years old. "I think we just found what we came for," Scott declared. It was a piece left over from the formation of the Moon. Unfortunately, the astronauts spent a lot of time getting core samples. As a result, they had to abandon plans to explore the mysterious craters that some scientists thought might be ancient volcanoes. But scientists were still anxious to discover whether any of this volcanism might be recent. Was the Moon still geologically active? No one knew. Apollo 16 would have to try to find the answer to this question.

Apollo 13 was headed for a landing in the Fra Mauro region of the Moon. On April 11, 1970, one of the oxygen tanks in the service module's electrical power system exploded. Mission control in Houston, Texas, ordered the landing to be canceled. The three astronauts had to continue on to the Moon but not land. They circled it before returning to Earth, because a spaceship cannot simply be turned around like a car or airplane. The astronauts had to depend on the oxygen reserves carried in the lunar module, which they used as a kind of "lifeboat" until once again arriving in Earth's orbit.

Astronauts John Young and Charlie Duke landed in hills near the crater Descartes on April 21, 1972. The region was filled with what looked like lava flows and ash falls. If there was any place that might reveal the secrets of lunar volcanic activity, this would surely be it. Unfortunately, the scientists were disappointed. Technical problems prevented some crucial experiments from being performed, while the Moon itself disappointed them. The signs of volcanic activity they'd hoped to find were nowhere in sight.

In 1972 Apollo 17 took the final trip to the Moon. The Apollo program was supposed to include twenty missions, but the U.S. Congress decided to cut the series short. After all, much of the reason for going to the Moon in the first place was political: to get there before the Soviets did. Once this goal had been accomplished, the politicians who were controlling NASA's budget thought that the United States had made its point. (Other landing sites would have included the crater Alphonsus. This location was known for strange phenomena-called transient lunar phenomena-such as glowing areas and cloudy patches. Another goal had been landing on the far side of the Moon, the side forever hidden from Earth.) Although the cancellation of the program was disappointing, NASA had no reason to be disappointed in the results of the Apollo 17 mission. The moonwalkers were astronaut Gene Cernan and geologist Dr. Harrison Schmitt-the first trained scientist to visit the Moon. They landed in Taurus-Littrow Valley, a rugged region that lies between two vast mountains.

Cernan and Schmitt spent a total of twenty-one hours and five minutes exploring the landscape. They traveled nearly 22 miles (35 km) in their Lunar Rover and accomplished a rigorous program of experiments. They set off explosive charges and measured the echoes received from deep beneath the surface. Since shockwaves travel differently through differentmaterials, the explosions allowed scientists to learn more about the Moon's crust.

During the mission, the astronauts discovered a patch of distinctly orange soil. This was a startling color to discover on the universally dark gray lunar surface. In fact, they had finally discovered signs of volcanic activity on the Moon!

Cernan and Schmitt also spent a great deal of time examining an enormous block of stone that had rolled down the mountainside. They named it Split Rock. When they left the lunar surface, it marked the end of the last human visit to the Moon. In the decades since then, no one has been back.

In fact, the Soviet Union never achieved the goal at all. The triumph of the Americans, combined with technical problems in developing a lunar spacecraft, convinced the Soviets to abandon their plans to send cosmonauts to the Moon.

Apollo astronauts brought back enough data about the Moon to keep scientists busy for decades. In fact, scientists are still studying these materials and learning new things about Earth's nearest neighbor. More than sixty research laboratories around the planet are devoted to studying Apollo data and samples.

Perhaps the most important question answered by the Apollo missions was "Where did the Moon come from?" In the past, there had been many theories, but none seemed to account for all the facts.