## Rocket Science

Thrust is the force that moves a rocket. It is generated by the rocket's motor, working according to Newton's third law of motion. As hot gases escape from the nozzle of the rocket, the reaction produces a force known as thrust. The more thrust a rocket has, the more it can lift and the faster it can go.

Thrust is calculated by multiplying the amount of gas being ejected per second by the speed of the gas. The more gas that is being ejected per second and the faster that gas is traveling, the greater the thrust will be. A rocket that weighs 1 ton (1 metric ton) and produces 1 ton (1 metric ton) of thrust will not go anywhere. This is because its weight and thrust balance each other exactly. Therefore, a rocket needs to have more thrust than its weight.

Another factor considered when building a rocket is mass ratio. This is the difference between the weight of the rocket when fully fueled and when empty. The greater this ratio is, the more propellant the rocket can carry and the greater its final speed will be. Most rockets have mass ratios between 6 and 20.

The Rocket's Wane

The rocket had proved itself in battle time and again. It was eventually adapted by many other countries, which formed their own rocket troops. But the rocket still had its faults. Chief among them was the long, cumbersome guide stick. The purpose of the stick was to help balance the rocket, enabling it to fly straighter than it would on its own.

Guide sticks were only partially effective, however. The entire rocket would be balanced at launch, but as its fuel was used up, its weight would change. The stick, however, never changed its weight. The balance of the entire rocket would eventually be thrown off, and it would veer off course. The long guide sticks also made the rockets difficult to transport.

A number of inventors sought to do away with the guide stick and stabilize the rocket in some other way. They had high hopes but unsatisfactory results. A British inventor named William Hale finally solved the problem by getting rid of the guide stick entirely. To stabilize his rockets, Hale inserted three curved metal vanes in the exhaust nozzle. These caused the rocket to spin rapidly when launched.

Making a projectile spin had long been recognized as the best way to achieve stability and straight flight. An arrow with its feathers set at a slight angle will spin as it flies and travel a straighter course. If a gun or cannon has spiral grooves on the inside of its barrel, the bullet or shell it fires will spin. Like the spinning arrow, it will fly straighter.

Such a bullet will also travel farther because there is less air resistance against it. The reason this works is centrifugal force. It is the same reason why a spinning top will not fall over. Newton's first law of motion states that once an object is set in motion, it will remain in motion unless acted upon by an outside force. This means that once an object is set spinning, it will resist any change in the direction of

The design of the Hale rocket (left) went through many refinements before the final version. The idea behind the design was to impart a spin to the rocket. This would stabilize it more effectively than the long, heavy, cumbersome guide stick used by the Congreve rockets (right), allowing the Hale rockets to be much more accurate.

The design of the Hale rocket (left) went through many refinements before the final version. The idea behind the design was to impart a spin to the rocket. This would stabilize it more effectively than the long, heavy, cumbersome guide stick used by the Congreve rockets (right), allowing the Hale rockets to be much more accurate.