How Rockets Fly, and how you can Fly Your Own

Our ancestors may have looked up at the stars and wondered what they were,but ever since we understood what they were, we then wanted to go there. Even the great astronomer Johannes Kepler wrote a fantasy story about going to the moon. In our time, we tend to take shuttle flights and rovers for granted. We have seen the volcanoes of Io and the ancient riverbeds of Mars. And still we reach out to space. Did you ever wonder just how NASA takes hundreds of thousands of pounds and sends it skyward into space?

The easiest way to begin to understand just how a rocket works is to compare itto a balloon with the air suddenly let out. If you blow up a balloon and then let go of it without securing the open end, the balloon will fly wildly around the room as the air inside forces its way out. The force moving the balloon is the reaction to the air leaving the balloon and it is called thrust. Thrust operates in the opposite direction of the air leaving the balloon.

Rockets fly pretty much the same way. Rockets generate large amounts ofhigh-pressure combustion gas in their engines, and this gas is ejected rearwards at high speed providing the force (thrust) that drives the rocket forward. A rocket is equipped with a combustion chamber and a nozzle. The combustion chamber is where gas is generated by burning fuel. The nozzle, the part that ejects the high-pressure and high-temperature gas, has a trumpet-like shape to increase the speed of the ejected gas. Since oxygen is required for burning fuel, and there is no air in space, the rocket must generate its own oxygen. For this, a rocket uses a material called an oxidizer, which must be carried by the rocket in addition to the rocket's fuel.

That is  one of the big differences between a rocket and a jet airplane. Thejet gets the oxygen for its engines from the air in which it is flying. Space is nearly a vacume, with no air and no oxygen. Unless the rocket carries its own oxygen, there is no way to burn the fuel it carries. Both the fuel and oxygen are referred to as the propellant. There are two types of propellant, liquid propellant and solid propellant.

A solid-propellant rocket has fewer parts and a simpler construction than aliquid propellant rocket. These features make a solid-propellant rocket more reliable, and easier to develop, manufacture and handle. It also costs less. In addition and can develop greater power (thrust) than a liquid-propellant rocket of the same size. The drawback is that once the fuel is ignited, it can no longer be freely turned on or off. So guidance and control are comparatively difficult.

The great advantage of a liquid-propellant rocket is that its thrust can beadjusted, making it easier to guide and control. After the fuel has been ignited, the tank valve can be closed to stop combustion. This allows several combustion tests before takeoff into space. The downside is its complex construction which makes development, manufacture and handling difficult. The Saturn rocket that launched the manned trips to the moon was a liquid-propellant rocket.

It has also been the thrill of rocket enthusiasts to build hobby rockets to launchout of the back yard. If you'd like to learn more about rockets, big or small, try one of these websites.

Space Team On-line, shuttle astronauts and space station
Space Team On-line:Rockets
Hitchhiker's Guide to Model Rocketry
Model Rocketry for Educators