Space exploration is traveling into space to gather information about the Earth, the moon, the planets, the stars, and other things in space. Space exploration could help people discover how the sun, the planets, and the stars were formed. People might also learn whether life exists on other planets. Some space exploration is done by people in spacecraft and some is done by spacecraft with robots or other equipment that gathers information. Image to right: An astronaut becomes a human satellite, flying free in space. A jet-powered backpack first used in 1984 allows astronauts to move outside the spacecraft without a safety line. Credit: World Book illustration What Is Space? The Earth is surrounded by air, which makes up its atmosphere. Beyond the atmosphere is outer space. There is no clear boundary between the atmosphere and outer space. However, most scientists say that space begins somewhere beyond 60 miles (95 kilometers) above the Earth. Satellites orbit the Earth just above the atmosphere. These satellites beam television programs and telephone calls all around the globe. Getting Into Space and Back A space mission must overcome the Earth's gravity. Gravity gives everything on the Earth its weight. It keeps us from floating away into space. The larger and heavier an object is, the harder it is to get off the ground. An artist's conception of the Sputnik satellite above Earth Large, heavy spacecraft need a powerful booster rocket to launch them. Boosters burn fuel that gives off gases in bursts that push the spacecraft off the ground and into the air. When the spacecraft reaches a certain speed, it breaks free of the Earth's gravity. A spacecraft fires a rocket again to increase its speed or to change direction. Image to left: The Russian Sputnik, the first artificial satellite, was launched into space on October 4, 1957. The satellite came out of a rocket and orbited the Earth for 94 days. Sputnik was the size of a basketball. It had four antennas that send radio signals back with information from space. Credit: World Book illustration To return to the Earth, a spacecraft must slow down. Once in the atmosphere, the spacecraft loses much of its speed. It begins falling toward the Earth. Parachutes slow it down even more. Some spacecraft, including the space shuttle, land like an airplane. They use wings to glide to a runway. The early United States space capsules "splashed down" into the ocean. Living in Space Spacecraft have systems that provide the astronauts with water to drink and air to breathe. They have heating and cooling controls to keep the temperature comfortable. Special toilets on board suck body wastes into collection equipment under the seat. Meals on spacecraft are easy to make and store. Some of these meals are frozen foods that can be warmed up on board. Trash is kept in unused places on the space vehicle. It is thrown overboard or brought back to the Earth. An artist's conception of a Russian spacecraft orbiting Earth Image to right: Russian cosmonaut Yuri Gagarin was the first person in space. On April 12, 1961, his spacecraft orbited the Earth once. The orbit took almost 1 1/2 hours. Credit: World Book illustration Astronauts wash themselves with wet towels. Some space stations, where space travelers live and work for long periods, have showers. Space travelers have special sleeping bags strapped to a cushion and a pillow. However, most astronauts like to sleep floating in the air. They just wear a few straps to keep them from bouncing around the cabin. Some astronauts wear blindfolds to block the sunlight that streams in the windows.

Staying Healthy in Space Astronauts eat good food in space to stay healthy. They ride exercise bikes, use treadmills, and perform other kinds of exercise to keep their muscles, bones, and hearts from growing weak. Some astronauts take medicine that makes them feel better in the weightless environment. Astronauts can enjoy the magnificent view of space from the spacecraft window. Space stations also have books, tapes, and computer games for the astronauts. Astronauts sometimes use entertainment to help them deal with feeling of homesickness and other emotional problems. Working in Space Astronaut John Young stands on the moon and salutes the U.S. flag Once they are in space, the crew members carry out the goals of their mission. They gather information about the Earth, the stars, and the sun. They experiment with the effects of weightlessness on various materials, plants, animals, and themselves. They also repair, replace, or build equipment. Some spacecraft bring supplies to space stations. Image to left: United States astronauts landed on the moon six times between 1969 and 1972. Apollo 16 astronaut John W. Young salutes a U.S. flag on the moon. Credit: NASA Astronauts use radio, television, fax machines, computers, and other equipment to communicate with mission control on the Earth. Computers tell the astronauts and mission control where the spacecraft is and where it is going. Astronauts wear space suits to work outside the spacecraft. A space suit can keep an astronaut alive for six to eight hours. The suit has many layers of material. It keeps the astronaut from getting too hot or cold and protects against small space rocks. Equipment in a backpack supplied the astronaut with air to breathe. A helmet blocks out strong, harmful rays from the sun. Thin, flexible gloves allow the astronaut to feel small objects and handle tools. The astronaut communicates with the crew and mission control through a radio.

History Space exploration began on Oct. 4, 1957. On that day, the Soviet Union launched the first artificial satellite to orbit the Earth. Yuri A. Gagarin, a Soviet cosmonaut, was the first human being to travel in space. He made his space flight on April 12, 1961. Astronauts on the outside of the shuttle in space holding a satellite Many space launches and developments in space exploration followed. The first human voyage to the moon was in December 1968, when the United States launched the Apollo 8 spacecraft. It orbited, or went around, the moon 10 times and returned safely to the Earth. In July 1969, U.S. astronaut Neil A. Armstrong became the first person to set foot on the moon. During the 1970's, astronauts and cosmonauts developed skills for living on space stations. Image to right: Shuttle astronauts have performed many challenging missions in space. In 1992, three astronauts worked outside the shuttle Endeavour to capture a communications satellite. Credit: World Book illustration In April 1981, the U.S. space shuttle Columbia blasted off. The shuttle was the first reusable spaceship. It was also the first spacecraft able to land at an ordinary airfield. Many space probes have also been launched into space. Space probes do not carry people. They have studied every planet. How to cite this article: To cite this article, World Book recommends the following format: "Space exploration." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.