There is no reason why a space-craft in orbit should not continue travelling round the earth for a very long time, since there is nothing to upset the balance of the forces which keep it in its place.

A man who is shut up inside such a small space, with only a limited amount of air, water and food, cannot stay alive for very long in those conditions. Apart from the strain on his body there is a very great strain on his mind. Space is very large and very lonely. Sooner or later he must be brought down to earth.

This is one of the most difficult problems which the space-scientists have had to solve. The hardest part is sometimes called the 're-entry problem'. It is not difficult to reduce the speed of the space-ship and allow the earth's pull to take effect. The important thing is to make sure that this happens gradually.

If the earth pulls it back unhindered, the speed of its fall through the air will make it so hot that the craft will burn up like a shooting star.

First the space-craft must spiral slowly towards the earth by firing the retro-rockets to check the speed. As it enters the atmosphere a parachute is released and this enables the astronaut to make a safe landing, hoping that if all has gone according to plan there are ships and aircraft to transport him safely back home to tell of his great adventure in space.