Article Outline
Rocket, self-propelled device that carries its own fuel, as well as the oxygen, or other chemical agent, needed to burn its fuel. Most rockets move by burning their fuel and expelling the hot exhaust gases that result. The force of these hot gases shooting out in one direction causes the rocket to move in the opposite direction. A rocket engine is the most powerful engine for its weight. Other forms of propulsion, such as jet-powered and propeller-driven engines, cannot match its power. Rockets can operate in space, because they carry their own oxygen for burning their fuel. Rockets are presently the only vehicles that can launch into and move around in space.
A rocket can be as simple and small as a firework, which has a small amount of thrust, or as complex and powerful as the Saturn V rocket, which took humans to the Moon. British Congreve war rockets, which were used in the War of 1812, are referred to in a line of the United States national anthem: “And the rockets red glare…” Rockets have many applications both on Earth and in space. The most common and well-known use of rockets is for missiles—weapons that deliver explosive warheads through the air to specified targets (see Guided Missile). Rockets also have numerous peaceful purposes. Upper atmospheric research rockets, or sounding rockets, carry scientific instruments to high altitudes, helping scientists carry out astronomical research and learn more about the nature of the atmosphere. Jet-Assisted-Take-Off (JATO) rockets help lift heavily loaded planes from runways. Lifesaving rockets carry lifeline ropes to ships stranded offshore. Ships in distress can launch signal rockets to signal for help. Rocket ejection seats safely boost pilots out of jet planes during emergencies. Fireworks have provided entertainment for centuries, and model rockets form the basis of a popular hobby.
People use all kinds of rockets for the same basic purpose: to carry objects through air and space. Missiles carry explosive devices to targets, while sounding rockets carry scientific instruments into the upper atmosphere. Launch vehicles boost satellites and other spacecraft into space, and smaller thruster rockets steer or stabilize spacecraft in space.
The term missile actually means any object thrown at an enemy and includes arrows, bullets, and other weapons. In modern military usage, however, missile usually means an explosive device propelled through the air by a rocket or an air-breathing engine. (Air-breathing engines differ from rockets in that rockets carry their own oxygen, while air-breathing engines get their oxygen from the air as they fly through it.)
Missiles can be launched from the ground, from airplanes, and even from submarines. Some missiles are designed to hit targets in the air, while others are built to hit targets on the ground. Some missiles, called guided missiles, have steering systems that guide them to their target.
Scientists use sounding rockets to carry scientific instruments into the upper atmosphere to take measurements of air quality, radiation from space, and other data. Many countries use sounding rockets to monitor weather and pollution. Engineers enable a rocket to reach its target altitude by shutting down the rocket at a specific height. The rocket then coasts upward until air friction and gravity stop its upward movement and cause it to fall back to Earth. The instruments usually include a radio transmitter that sends measurements back to Earth. Some sounding rockets carry parachutes that allow their controllers to recover the rocket and the instruments, but some fall back to Earth without a parachute. Engineers design a sounding rocket’s flight path so that the rocket will fall into the ocean or into an uninhabited area in order to avoid damaging property or hurting people.
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