In addition to the role they play in space exploration, scientific research, and the military, rockets are also an important part of many cultures around the world. Traditional Fourth of July skyrockets have been a familiar part of Independence Day celebrations for nearly two hundred years. They serve to remind Americans of the rockets that fell on Fort McHenry during the War of 1812.
In Mexico many saint's days are celebrated with fireworks and rockets. Of course, Chinese New Year wouldn't be complete without rockets, especially in the culture that had originally invented them. Perhaps the most extraordinary cultural use of rockets is the enormous festival rockets of Japan and Southeast Asia. In Thailand and Laos, they are called Boun Bang Fai rockets, meaning "the merit of firing rockets." They have deep roots in Buddhist and traditional symbolism.
These rockets, built and launched for perhaps as long as one thousand years, are enormous constructions. They are hand made from bamboo and paper and lavishly decorated with colored foil, banners, garlands, tassels, and dragon heads. They may be as large as 6.5 to 13 feet (2 to 4 m) long with bamboo guide sticks up to 45 feet (13.7 m) long. Filled with up to several hundred pounds of gunpowder, these beautiful rockets rise 300 to 500 feet (90 to 150 m) into the sky.
Southeast Asian festival rockets are hand made by villagers using techniques unchanged for hundreds of years. These giant rockets are launched during special religious festivals such as this one in Thailand.
principle of action-reaction. Something is ejected at high speed from one end, causing the rocket to move in the opposite direction. This "something" in the rockets we've described so far has been a hot gas, produced by burning fuels. But it does not have to be a hot gas. Whatever is being ejected must be done so at a very high speed. When you blow up a balloon and release it, it will fly around the room like a rocket because of the reaction to the air it is expelling—and that air is not even hot, let alone burning.
Modern engineers work on rocket systems that Goddard and von Braun would have never dreamed of. Nuclear-thermal rockets (top) may take explorers to Mars. The Pulse Detonation System (middle) is a chemical-fueled descendant of the Orion Project. Rockets may even be powered by microwaves instead of hot gases from burning fuels (bottom).
Back in the 1920s, several scientists, including Hermann Oberth, suggested that matter could be ejected at high speed by electricity. Ionic air filters are a good example of how electric rockets work. Two metal plates are given opposite electrical charges. Air is drawn into one side of the filter and given a positive charge by one of the metal plates. It is then repelled by the positive charge of the second plate, since similar electrical charges repel one another. This creates a stream of air flowing through the filter. This same effect can create a stream of gas flowing from the engine of a rocket. Electric rocket engines are often called ion thrusters because an atom with an electrical charge is called an ion.
There have been many different plans for ion rockets since the 1920s, but all work more or less on the same principle. First, a gas is given an electrical charge. Then it is propelled from the nozzle of the rocket by passing it through a grid bearing the same electrical charge as the gas. Engines such as this produce low thrusts, but they also require little fuel. It almost seems as though they can run nonstop indefinitely. So although an ion rocket starts off slowly, its exhaust eventually builds up to tremendous speeds. The actual thrust, however, is very low, so ion engines can be used only in space and not to launch spacecraft from Earth.
Ion engines have been successfully tested in space. They have been used on satellites as efficient, low-thrust engines for adjusting the position of the spacecraft. An ion engine was used on a Japanese space probe that made a historic touchdown on an asteroid in 2005. The Hayabusa spacecraft, using the gentle nudges from a NASA-developed ion engine, scooped up samples of the surface of asteroid Itokawa for eventual return to Earth. A soil sample from an asteroid will yield clues about the raw materials that made up the planets and asteroids in their formative years. Even the smallest sample from an asteroid can have huge scientific value.
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