Rockets Through Space by Lester Del Rey

Author:Lester Del Rey [Rey, Lester Del]
Language: eng
Format: epub
Published: 2013-09-17T04:00:00+00:00

Then there is gravity. About this we know even less. We know the rules that matter obeys when pulled by gravity, but almost nothing about what gravity is. The Earth’s gravity grows weaker as we move out from the surface, and we can figure out how strong it will be. The rule is that gravity decreases with the square of the distance from the center of Earth. This means that if we go out 4,000 miles into space, we are twice as far from the center of Earth. So we square 2—multiply it by itself—to get 4, and divide the gravity pull by that figure, leaving us with only 1/4 normal weight. At 36,000 miles distance, we are 10 times as far from Earth’s center, so we weigh only 1/100 as much as we do on our planet. From then on. we keep growing lighter and lighter, but never quite lose all our weight, unless we reach a place where the pull of something else (such as the Moon) exactly equals that of Earth.

It is also not quite accurate to state that all the space between the planets and moons is empty. Most of it is so empty that we can forget about the few molecules there, or the little motes of dust. There are, nevertheless, a few objects traveling in even this empty space that we cannot overlook.

These bodies are the meteorites. Most people who have seen science-fiction movies or read stories about travel in space already know about them. In fact, according to some of the stories, it might almost seem that a ship could hardly get out of the atmosphere before being hit and battered by such meteorites. Happily, the situation is not nearly that bad.

It is true that millions of these meteorites strike the atmosphere of Earth every day. It is also true that these bits of stone or iron travel through space at speeds as high as 25 miles a second. This does not mean that a spaceship will be in constant danger from them.

In the first place, Earth is much larger than any spaceship we can ever build. It presents a target to the meteorites of close to 100 million square miles, and our spaceship will have an area of only a small fraction of 1 square mile to be hit. That reduces the number of hits by a proportion of a billion to one, or more!

In the second place, most of the meteorites that hit are too small to matter much. Most of them are tiny bits, no bigger than the particles of dust that float in the air. They may strike with tremendous energy for their size, since their speed is so high, but even the thin skin of the rocket would stop them without any serious damage. (Also, remember that these particles will often be going around the Sun in the same direction as Earth, which itself is traveling at 18 miles a second; hence the difference in speed between the meteorites and a rocket near Earth will not be so great as it seems.

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