Rockets

The traditional definition of a rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving fluid from within a rocket engine. Often the term is also used to refer to a rocket engine. more...

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Overview

Uses

In military use, rockets generally use solid propellant and are unguided. Rockets equipped with warheads (representing a form of missile) can be fired by ground-attack aircraft at fixed targets such as buildings, or can be launched by ground forces at other ground targets. During the Vietnam era, there were also air-launched unguided rockets that carried a nuclear payload designed to attack aircraft formations in flight. In military terminology, the word missile is often preferred over rocket when the weapon uses either solid or liquid propellant, and has a guidance system. (This distinction generally does not apply to civilian or orbital launch vehicles.)

Rockets are used to accelerate, change orbits, de-orbit for landing, for the whole landing if there is no atmosphere, e.g., for landing on the Moon, and sometimes to soften a hard parachute landing immediately before touchdown (see Soyuz spacecraft).

Operation

In all rockets, the exhaust is formed from propellant, which is carried within the rocket prior to its release. Rocket thrust is due to the very fast release of exhaust gases (for more info see Newton's 3rd Law of Motion).

Types

There are many different types of rockets, and a comprehensive list can be found in spacecraft propulsion — they range in size from tiny models such as water rockets or small solid rockets that can be purchased at a hobby store, to the enormous Saturn V used for the Apollo program.

Most current rockets are chemically powered rockets (internal combustion engines) that emit an exhaust gas. A chemical rocket engine can use solid propellant (see Space Shuttle's SRBs), liquid propellant (see Space shuttle main engine), or a hybrid mixture of both. A chemical reaction is initiated between the fuel and the oxidizer in the combustion chamber, and the resultant hot gases accelerate out of a nozzle (or nozzles) at the rearward-facing end of the rocket. The acceleration of these gases through the engine exerts force ("thrust") on the combustion chamber and nozzle, propelling the vehicle (in accordance with Newton's Third Law). See rocket engine for details.

Not all rockets use chemical reactions. Steam rockets, for example, release superheated water through a nozzle where it instantly flashes to high velocity steam, propelling the rocket. The efficiency of steam as a rocket propellant is relatively low, but it is simple and reasonably safe, and the propellant is cheap and widely available. Most steam rockets have been used for propelling land-based vehicles but a small steam rocket was tested in 2004 on board the UK-DMC satellite. There are proposals to use steam rockets for interplanetary transport using either nuclear or solar heating as the power source to vaporize water collected from around the solar system.

Read more at Wikipedia.org