5. The Moon: stepping stone to the planets

Expeditions to the Moon

Race to the Moon

The Space Age began on 4 October 1957, when the Soviet Union launched the first artificial Earth satellite, Prosteyshiy Sputnik, the simplest satellite. Two years later the Soviets launched their Luna 3 probe that was sent around the Moon, taking the first pictures of the normally invisible far side. And on 12 April 1961, cosmonaut Yuri A. Gagarin became the first human in space, orbiting the Earth in the Vostok 1 capsule. Soviet officials used these accomplishments in a Cold War with the United States, citing them as evidence that communism is a superior form of social and economic organization.

Stimulated by the worldwide excitement generated by the first human fight in space, the brave, visionary young President, John F. Kennedy, decided that the United States had to surpass the Soviet Union in some dramatic way in space. After expert advice, he concluded that there was a good chance of beating the Soviets to the first manned landing on the Moon. On 25 May 1961, just six weeks after the Gagarin flight, Kennedy delivered his now-famous address to a joint session of Congress, including the declaration: "I believe that this nation should commit itself to achieving the goal, before the decade is out, of landing a man on the Moon and returning him safely to Earth". The president's call to action struck a responsive chord in the American public and galvanized their space program.

The Apollo program

The Apollo spacecraft was designed to carry three men into orbit around the Moon. A small, Spartan landing craft, the Lunar Excursion Module or LEM for short, would ferry two of the crewmen from lunar obit to the Moon's surface and then back to the mother ship, while the third astronaut remained orbiting the Moon in the larger Command Service Module.

Fig. .. 

On 21 December 1968 three Apollo 8 astronauts became the first humans to break free of the Earth's gravity. Although the crew would only orbit the Moon and not land on it, the unprecedented voyage provided the first sight of the Earth seen from afar - a radiant blue-and-white sphere rising beyond the battered face of the Moon in the dark void of space. We then saw our home world in a new perspective, beautiful and vulnerable, a tiny, fragile oasis shimmering all alone in the vast, deep chill of outer space. The sheer isolation of the Earth became plain to every person on the planet. It stimulated a world-wide awareness of the Earth as a unique and vulnerable place, fostering the ecology movement and helping us to get a better feeling for planet's place in our lives and the Universe.

On 20 July 1969, the spindly-legged, Lunar Module Eagle carried two Apollo 11 astronauts to the lunar surface. While an estimated half-billion people watched, Neil A. Armstrong took the controls to avoid a hazardous crater, and radioed the first words from another world "Houston, Tranquillity Base here. The Eagle has landed". It was enough to take your breath away.

Fig. .. 

In all, twelve humans have walked on the lunar surface, to gather samples, take photographs and make other scientific measurements. All of the landing sites were on the near side and close to the lunar equator because these were the only places the astronauts could go safely. Direct radio contact from Earth would be lost if they landed on the far side of the Moon. Sites near the equator were chosen to always be able to get astronauts back from the lunar surface quickly in case something bad happened down there. A landing near the edge or limb of the Moon, as viewed from Earth, was ruled out if the spacecraft was to return to Earth in daylight. Within these constraints, the landing sites were chosen to provide samples of wide variety of terrain, from the smooth maria to the heavily cratered highlands.

Fig. .. 

The astronauts' cameras recorded an eerie wasteland below a blackened sky, battered and scarred with craters of all sizes and covered with dust. It clung to the astronauts' clothing and equipment and showed the sharp outline of their footprints; but there were no clouds of dust above the airless surface. Walking on the lunar surface was like walking on plowed soil or wet sand, and most of the finer dust had evidently been plowed down into the Moon by the churning of the meteorites.

Fig. ..  Fig. .. 

Armstrong and Aldrin never strayed more than a hundred meters from their lander, like a timid child testing the water when entering a lake or sea for the first time. The astronauts of the next two missions (Apollo 12 and 14), had greater confidence and took longer moonwalks. During the last three missions (Apollo 15, 16 and 17) astronauts roamed as far as 7 thousand meters from the landing site, visiting some of the most spectacular places on the Moon in a battery-powered car called the Lunar Rover.

Fig. .. 

The astronauts left behind the Apollo Lunar Surface Experiments Package, abbreviated ALSEP. This nuclear-powered array of instruments included seismometers to monitor vibrations of moonquakes and meteorite impact, magnetometers to measure possible magnetic fields, and other instruments to analyze gases and charged particles streaming from the Sun to the Moon. The astronauts also brought lunar soil and rocks back home with them, altogether 382 kilograms and not an ounce of cheese.

Return to the Moon

Fig. .. 

After the Apollo missions, no one had even a single glimpse of the Moon's far side for nearly two decades, and then it was obtained by the Galileo spacecraft on its way to explore Jupiter's realm. In order to reach the giant planet, Galileo pumped up its orbit and gained speed by swinging past the Earth, once on 8 December 1990, just 14 months after launch, and again on 8 December 1992, passing by the Moon in the process. It obtained images of the lunar limb and far side from vantage points not previously obtained. For instance, the Sun illuminated the western limb of the Moon during the 1990 Galileo flyby, while sunlight brightened the opposite eastern limb during all of the Apollo missions.

Fig. .. 

Composites of Galileo images taken in three colors, violet, red and near infrared, have been used to depict compositional variations of the lunar surface. They have been calibrated by Apollo sample returns that specify the chemistry at specific sites on the near side of the Moon. Some mare basalts are rich in titanium, while many others are relatively low in titanium but rich in iron and magnesium. The heavily cratered highland are typically poor in titanium, iron and magnesium.

Fig. .. 

In early 1994, the United States Department of Defense placed the small Clementine spacecraft in orbit about the Moon. Like its namesake, the spacecraft was "lost and gone forever" after orbiting the Moon for two months, but not without first chalking up an impressive list of accomplishments. Unlike the Apollo Command Modules, that circled the Moon in low, near equatorial orbits, Clementine orbited across the lunar poles, permitting a global perspective as different regions rotated into view. The surface composition and topography of the entire satellite were mapped in unprecedented detail, the South Pole - Aitken basin was completely mapped with high resolution for the first time, and possible deposits of water ice deposits were found in the cold permanently dark places within the poles.

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Copyright 2010, Professor Kenneth R. Lang, Tufts University