Round the Earth

A date which will go down in history books for a long time to come is October 4th, 1957. This was when the Russian scientists launched the first earth satellite. It has since been followed by many others, some carrying the first men into space.

As our earth and the other worlds belonging to the sun's family travel along their orbits, we may wonder what keeps them on their right course. One thing is the pull of the sun's gravity. If it acted alone this would pull all the planets into its vast furnace, where they would melt like snowflakes. The other force is one which comes from their movement. This tends to throw them out into space like a stone which is being swung round on the end of a string. These two forces just balance.

If a satellite is launched at a high speed, it may go far away from the earth and be lost. If the speed is not high enough it will fall back and be burned up as it rushes through the air. If we want the satellite to travel round the earth, it must be sent at the right speed, and this varies according to the distance of the orbit from the surface of the earth. If we want it to travel round at a height of two hundred miles it must have a speed of about eighteen thousand miles an hour. At this speed it can go on travelling round the earth for many years.