A rocket is the only vehicle which can journey into the vacuum of space - that is, the vast part of space that has no air. Other means of transport require friction (asd) the wheels of a train) or air for "lift" (as required by a balloon), while all need air in which to burn their fuel whether it is the petrol in a motor-car or the oil in a ship.
A rocket is independent of air because it contains an explosive mixture which consists both of a fuel to be burned and a supply of oxygen. When these are burned, the result- ing thrust caused by the extremely hot and expanding gases can be controlled and directed to push the rocket in the re-quired direction.'The power got from some of the chemi- cals is enormous, which is just what is required to get over the pull of the earth's gravity, which would otherwise bring the rocket back to the earth's surface again.
The rocket itself seems to have been invented in China in the 12th century. There is a record of it being used in the siege of Peking in AD, 1232, and there is even a story of a Chinese official of the 15th century who harnessed 47 large rockets to a chariot, though this brought him to an untimely end.
By the 17th century rockets were used in many coun- tries as weapons of war. They were similar to the present- day firework, consisting of a cylindrical tube into which were pressed the chemicals to be burned, i.e. the pro- pellants. Usually this mixture was gunpawdcr.
As the rocket propellants burn, they make vast quanti-ties of gas, which press outwards against the tube in all direc-tions. This gas escapes freely through the nozzle, so there is no pressure there, but the gas p-essing against the opposite end pushes the whole rocket forward This can be seen in the case of a balloon. If it is blown up and the neck then released, the internal pressure of air on the side opposite to the neck will make it move in that direction.
This shows that the pushing is being done from inside. As long as there is an internal pressure, i.e. for so long as the rocket burns its propellant, it will continue to go faster and faster. The flaming exhaust is not doing any pushing at all, but only escaping freely. The more easily it can esca-pe, the faster will the rocket move. This shows that a roc- ket will work best in a vacuum, where there is no air either to slow d 3wn the exhaust or cause air resistance at the nose.In other words, the rocket works best in space and is the ideal vehicle for space journeys.
