In this age of alphabetized terms such as ICBM, IRBM and a myriad of agencies controlling or working with missiles, we are all aware of the fact that there is a phenomenon called rocket power or rockets. Each week brings the news of another success or attempt to shoot a missile into space by the use of various rockets.
The history of the rocket is not of only recent times but has been on the scene for many years, our grandparents seeing them in very simple form. Perhaps one of the oldest uses or rocket power is that of shooting Fourth of July fireworks high in the air to produce the spectacular. These devices even bore the name rocket in their title of sky-rockets. Rockets as the power plant in weapons of destruction came into use in the last world war in the form of the bazooka and recoilless rifles. When the Germans introduced their powerful V-2 rockets these missiles became terrible destructive weapons of their time. Since that time the rocket has become highly refined and developed so that today it is the “ultimate” weapon in the hands of men.
In the foregoing paragraph I have talked about rockets in rather general terms that do not speak of rockets as to their true characteristics. In the strict sense of the term rocket, the meaning describes the means of propulsion and does not refer to the destructive power of a missile. Rocket power can be defined as the projection of an object through space by the reaction resulting from the rearward discharge of gases liberated by combustion. A rocket motor consists essentially of a combustion chamber and an exhaust nozzle, and is supplied with either liquid or solid propellants which provide the fuel and the oxygen needed for combustion, thus making this engine independent of the oxygen of the air.
This then is the formal definition of rocket power and motors. Now for a look at how such a motor can operate. The principle on which such a motor operates was stated in the Eighteenth Century by the famous scientist, Sir Isaac Newton, in his third principle of motion; for every action there is an equal and opposite reaction. What does this mean? A few common examples of the occurrence of this principle in our daily life should help to explain it. Perhaps some of us have had the misfortune of stepping out of a boat on to a landing only to find that our step out of the boat has moved the boat away from the landing so that we stepped into the water instead of on the landing. The action in this example is the pushing by means of our muscles to move our body out of the boat. The opposite and equal reaction is that the boat also moved because of this force. The fact that the boat seems to move much more than we do in this case does not reduce the fact of equal reaction but is the result only because it is more easily moved and moves farther than our body. Some other common examples would be running on ice and having our feet slide as much on the ice in a backward direction as we are moving forward. Other examples are the wind caused by the turning of airplane propellers, or movement of water caused by a ship’s propellers. Much of this equal and opposite reaction to our actions goes unnoticed because we have learned to perform actions so that this reaction is prevented in the form of motion. We walk on substances on which our feet do not slip, we equip the wheels of our vehicles with tires that will not slip. The reaction is there but is not in evidence as motion.
Now how does a rocket engine fit into the picture of action and reaction? Let’s take a simple example of a rocket engine, and inflated balloon. If the balloon is released the air rushes out of the opening. This column of air can either rush out of the balloon causing air movement or the balloon can move ahead to move away from the escaping air. In practice both happen, the action of air rushing out of the balloon and the balloon moving away from the rushing air. Now someone is sure to say, but the balloon moves because the escaping air is pushing against the air in the room making the balloon move. This is true, but the balloon must also move against that same air; if it were possible to release this balloon in a vacuum there would still be motion.
The question now comes to our minds what is the difference between a rocket engine and a jet engine. As far as the principle on which they are able to move is concerned there is little difference, they both move by the rearward discharge of gas. The jet engine cannot operate outside of the atmosphere because it needs that atmosphere to supply oxygen for combustion, not for a medium to push against as in the case of a propeller driven object. The rocket engine is self-contained carrying within the fuel the oxygen needed for combustion, hence it can operated where there is no atmosphere. In this factor we can see why rocket powered missiles are such heavy objects before they begin their flight, because they must not only carry a fuel supply but an oxygen supply as well.
In this characteristic or rocket engines is seen the reason why they are the only means of propulsion in space. They are a self-contained engine not dependent on outside factors for movement. At the same time this makes these engines quite weighty. Perhaps you have wondered why such tremendous amounts of fuel were needed to project comparatively lighter objects into outer space. An analogy can be made between this engine and a man traveling across a desert. Because there is no food for him on the desert he must carry his own. If this man cannot carry enough food for himself he must acquire a pack animal to carry the load, but in turn this animal needs food so again the load is increased. More animals are added and more food added, perhaps another person added to help direct and care for the animals and then again more animals and food until a balance is reached so that the amount of food and water balances the need. The object of this trip is to move one man across the desert but in order to do that a large caravan is organized for the seemingly light task. To propel a small object a great distance by rocket power can be compared to the desert expedition. Every pound of fuel needed needs more fuel to move it, and more equipment and more fuel until the proper balance between load and fuel is achieved.
The process is not as endless as it may appear so that travel in space by rocket power depends on the building of bigger and bigger missiles to carry the fuel. The obvious solution of the problem in both the rocket powered missile and the desert expedition is to find more potent fuel so that less of it needs to be carried along and thus lightening the load and reducing the need for the load. This process can be continued so that as a more and more powerful fuel, or food, is found the loads become lighter and lighter until it goes to the opposite extreme of great size, a very small missile that will travel vast distances. This is the dream of missile and rocket engine designers.
In this discussion of rocket engines as to their characteristics, advantages and limitations the problems of present day space travel can be visualized. The fact of its slow development and questions of its fulfillment are more fully understood. Man’s trip into space can be likened to that long trip into the desert, for indeed travel in space is travel into a huge and almost endless desert. In order to make the trip and return to the oasis of earth does indeed involve the equipping of a huge caravan to carry all the needs of that one man and the power to move all that equipment. This trip is a double trip into a desert for the man must not only carry his food along, but also the atmosphere in which he has to live, for the desert of space not only denies him food but also the air that he was created to live in. Indeed this is a gigantic undertaking in trying to take man out of his God-created place on this earth and for a short period of time lift him away from it. The big question is still, can it be done?
Originally Published in:
Vol. 19 No. 5 June-July 1959