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The Science of Astronautics
The Space Age began with the launching of the artificial satellite Sputnik 1 on October 4, 1957. Less than four years later, on April 12, 1961, came the first manned flight. The Russian Yuri Gagarin made one orbit of the Earth in his spacecraft Vostok 1. He was the first space-pilot, or astronaut. (The Russian term is cosmonaut.) After years of preparation, the United States landed a manned spacecraft, Apollo 11, on the Moon on July 20, 1969. In the next few years several more successful Moon landings were achieved by the United States, and valuable scientific experiments were carried out. Later astronauts were helped in these by the small vehicle, or 'Moon buggy', they took with them.
A spacecraft is carried into space on top of a massive rocket, which lifts it clear of the Earth's atmosphere and gives it the very high speed required to keep it in orbit or propel it to the Moon.
A spacecraft can stay in orbit if it has enough speed to overcome the 'pull' of the Earth, or gravity. For an orbit 160 km above the Earth, this orbital velocity is about 28,000 km/h. At this distance and orbital velocity the tendency of the spacecraft to fly away from the Earth (like a stone from a sling) is balanced by the pull of gravity.
There is, then, no effective gravity in orbit. Everything is therefore weightless. This state is often called zero G, G standing for gravity.
The spacecraft must be lifted above the Earth's atmosphere to avoid the resistance, or drag, of the air. Drag would quickly slow it down and make it fall back to Earth. Also friction with the air would heat the craft and might even make it burn up, just like a meteor does.
Launching an astronaut into space and bringing him back is a very hazardous business. To start with, he has to withstand the great forces of acceleration during take-off. Then he must adjust to the effects of weightlessness in orbit. He must be protected by his spacecraft or a space-suit from the cold and airless world of space. Finally, on his return from space, he must survive the rapid slowing down and heating effects caused by the drag of the atmosphere.
Astronauts receive special training to prepare themselves for space flights For example, they spend a long time in a machine called a centrifuge, which whirls them round and round rapidly and reproduces the kind of forces they can expect during take-off and landing.
The astronauts also train in dummy spacecraft which can be made to do many of the things a real one does in space.
After months of intensive training, the astronauts climb into their spacecraft and are rocketed into space. They lie on their backs during launching because this is the best way to withstand the great 'push' of the rocket.
Up in space the astronauts, like everything else, are weightless. Nothing keeps them 'down', and they can float around freely. Eating and drinking are very different from on Earth. Food and drink must be squeezed right into the mouth.
The crew cabin of the spacecraft is connected to what is known as a life-support system. This provides gas under pressure for the astronauts to breathe, removes stale air and moisture, and keeps the temperature steady.
Returning to Earth is probably the most dangerous part of the space flight. To fall down from orbit, the spacecraft must be slowed down to below orbital velocity. This is done by firing rockets called retro-rochets in the direction in which the spacecraft is travelling.
After the retro-rockets have fired, the capsule containing the astronauts separates from the rest of the craft. It drops rapidly towards the Earth and re-enters the atmosphere. The atmosphere acts like a brake and quickly slows down the capsule and heats it at the same time. The base of the capsule glows red-hot, but it is specially designed as a heat shield to protect the astronauts inside. As the capsule falls lower, parachutes open and gently lower it to the ground or the sea.