ASTRONAUTICS

This is the branch of science which deals with the many problems of space flight.

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 space craft Vostok 1. He was the first space pilot, or astronaut. (The Russian term is cosmonaut.) The first American astronaut to orbit the Earth was John Glenn. Glenn made three orbits on February 20, 1962. After years of preparation, the United States landed a manned spacecraft, Apollo 11, on the Moon on July 20, 1969. Two American astronauts, Neil Armstrong and Edwin Aldrin, spent 21 hours on the moon, including a 2hours and fifteen minutes’ walk. On November 19, 1969, two other American astronauts landed on the Moon and spent over seven hours walking on its surface.

A spacecraft is carried into orbit 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. A spacecraft can stay in orbit if it has enough speed to overcome the 'pull' of the Earth, or gravity. For an orbit 100 miles above Earth, this orbital velocity is about 17,500 miles an hour. At this distance and orbital velocity the tendency of the spacecraft to fly away from 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 gravity must be lifted above the Earth's atmosphere to avoid the resistance, or drag, of the air. Drag would quickly slow it down quickly and make it fall back to Earth. Also friction with the air will 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 spacesuit from the cold and airlessness of space. Finally, he must return from orbit and survive the rapid slowing down and heating effect caused by the drag of the atmosphere.

Astronauts receive special training to prepare themselves for space flights. For example they spend time for a long time in a machine called a centrifuge. This 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 the orbit 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 their 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-rockets in the direction in which the spacecraft is travelling. After the retro-rockets has 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 grows red-hot, but it is specially designed as a heat shield to protect the astronaut inside. As the capsule falls lower, parachutes open and gently lower it to the ground or the sea.