Navigating in Space

            On earth there is one big, powerful force – the earth's gravitation. Even though the rest of the universe is pulling also, we don't have to think about it. The earth's pull is much stronger because we're close to it. But out in space, every pull matters. The gravitation of every object – every star, every planet, every moon, and even smaller objects – can pull the spacecraft out of its course. Steering it back into its course is difficult.
            It's not like steering a car or plane. Spacecraft is steered by jets of gas from a tank, and there's room for only a certain amount. So the navigator must plot his correct course way ahead, rather than make mistakes which he may not be able to correct.

Where does space begin?

            Space begins where the earth's atmosphere is very thin – so thin that it has little effect on objects moving through it. But you can't see space. Astronauts in flight, however, can tell when they have moved into space. The instruments show that the air pressure outside the spacecraft is zero. Also, anything not firmly held down floats in the cabin. Things seem to be weightless. This is because objects within the spacecraft really are falling toward the earth. If they were not in a fast-moving spacecraft, they would fall. But objects in the spacecraft have the same motion as the spacecraft, so they float in midair. When this happens, the astronauts are at least 160 kilometers (100 miles) above the earth. They are in space.
            As the spacecraft continues into space, it passes through the earth's magnetosphere. the magnetosphere is the region around the earth where the earth's magnetic field acts. The magnetosphere helps protect the earth from solar radiation caused by solar flares. Astronauts within the magnetosphere are also protected from dangerous radiation in space.

Launching spacecraft

            It is not easy to get beyond the earth's strong pull of gravity. Huge rockets or combinations of rockets are needed to send any spacecraft into space. These launch vehicles, as they are called, carry heavy loads of liquid or solid fuel. When burned, these fuels give the spacecraft the thrust, or push, it needs to reach the proper speed and direction for its flight into space.
            Most launch vehicles are made up of stages. The first stage is the bottom and largest rocket. This rocket lifts the spacecraft and gives it some speed. It drops off after its fuel is used up.
            After the first stage drops off, the second stage fires to speed up the spacecraft even more. As the second stage uses up its fuel and drops off, the third and final stage has reached its desired position and speed. The spacecraft then goes into orbit around the earth.
            Once a spacecraft is in orbit, it may need to make corrections in its speed and direction. For this purpose, smaller rockets are located at various places on the spacecraft. When the rockets in the rear are fired, the spacecraft is speeded up. When the rockets in the front are fired, it is slowed down. Rockets fired from the sides change the spacecraft's direction.

To the moon and back

            Suppose you want to send a spacecraft into orbit around the moon. First you must launch it into orbit around the earth. To do this, three rocket stages are fired. After orbiting the earth, the third stage of the rocket is fired again to boost the spacecraft's speed up to 39,110 kilometers (24,300 miles) per hour. This pushes the spacecraft out of earth orbit and sends it toward the moon. At this point, the third-stage rocket drops off.
            The earth's gravity will pull on the speeding spacecraft until it slows down to about 3,200 kilometers (2,000 miles) per hour. By that time though, the spacecraft is close enough to the moon to be affected by the moon's gravity. The moon's gravity causes the spacecraft to be speeded up again. When the spacecraft draws nearer to the moon, it has to be slowed down to get it into orbit around the moon. To do this, rockets are fired from the front of the spacecraft.
            What if you were aboard the spacecraft and wanted to land on the moon. You would probably have a lunar module attached to your spacecraft to do this. After you enter the lunar module, you can separate it from the orbiting command module that will take you back to the earth later on. By firing rockets from the front of your lunar module, you can slowly descend to the surface of the moon.
            When you want to leave the moon, you will have to use part of the lunar module as a launching pad. You can fire rockets to send the part of the lunar module in which you are traveling into orbit around the moon. There you can dock with and enter the command module. When the lunar module separates from the command module, you can fire another rocket to get you out of moon orbit and on your way back home.

What's different about being in space?

            People in space have the same needs as people on the earth. they need food, water, oxygen, and shelter from exposure to heat and radiation. None of these things is provided in space. So for shorter trips of up to a few months, these things must be carried from the earth. On longer trips, green plants can be grown in the spacecraft to provide both food and oxygen. Water can be recycled. The spacecraft itself protects its passengers from heat and dangerous radiation.
            When astronauts leave their spacecraft, they have to have a radio set with them so they can talk to one another. Even when they are next to one another, the sound of their voices cannot be carried from one to another in space except by radio waves.
            Before astronauts were first sent into space, scientists had to experiment a great deal to find out how the human body might react in space. They knew that people in space would experience weightlessness. People and objects float when they are weightless. Because of this, eating has to be carried out differently in space. Eating while upside down is not out of the question!
            The food taken into space is often freeze-dried. That means it is frozen after the water in it has been removed. When astronauts want to eat freeze-dried food, they have to inject hot water into the food container. Then, to keep crumbs from floating about the cabin, food is squeezed from the container into the mouth. Or food like beef stew can be eaten with a spoon, but the food must be carefully handled. If an astronaut suddenly slows down the motion of raising the spoon, the food may leave the spoon and land in the astronaut's eye!
            Astronauts in space for long periods of time have to exercise regularly to overcome some of the effects of weightlessness. Their blood doesn't weigh anything in space. So their heart has less work to do in pumping blood throughout the body. This could cause the heart to become lazy and unable to work properly on returning to the earth. All their muscles would become weak without exercise.
            Astronauts can perform many tasks in space. but they have to learn how. When doing repair work, they have to anchor themselves somehow. Even turning a handle can send them into a spin. Every tool they use must have a secure storage place. If not, it will just float around.