Wondering about the stars and the planets in the sky prompted early humans to study their motions (see astronomy). As scientists’ understanding of the solar system and the universe improved, people developed an urge to travel beyond Earth. In many times and places, stories of people flying up to the stars or to the moon circulated.
It took centuries before people could rise a short distance above the Earth’s atmosphere with kites, balloons, and airplanes. These devices depend upon the air that surrounds them for support and to burn their fuel. Rockets that use liquid fuel and multiple stages let humans travel much farther. Konstantin Tsiolkovsky, a Russian schoolteacher, developed the basic rocket equation, which lets engineers figure out how high a spacecraft can fly if its mass, fuel, and exhaust velocity are known.
Spacecraft that carry people are among the most complex devices ever designed. They must function as both spacecraft and airplanes, with wings, rudders, stabilizers, and wheels. Spacecraft that carry people must also be pressurized, so that occupants can breathe.
In 1957 the Soviet Union launched a dog named Laika into space aboard the satellite Sputnik 2. She survived the acceleration and weightlessness of launch, but died five hours later when her telemetry transmitter failed. This and other animal experiments helped people determine that, if properly protected, human beings can survive and work in space.
Since the 1950’s, nations have planned and built space colonies on the Moon, Mars, asteroids, and in orbit around the Earth. These can serve as research centers for unique or risky investigations and as sites for factories, observatories, or mining stations. Some also provide information on how human bodies, hearts, and minds react to long stays in space.
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