A rocket is a missile, spacecraft,
aircraft
or other vehicle
that obtains thrust from a rocket
engine. In any and all rockets, the exhaust is formed entirely from
propellants
carried within the rocket before use.
Rocket engines work by action and reaction. Rocket engines push
rockets forward simply by throwing their exhaust backwards extremely
fast.
While comparatively inefficient for low speed use, rockets are
relatively lightweight and powerful, capable of generating large
accelerations and of attaining extremely high speeds with reasonable efficiency. Rockets
are not reliant on the atmosphere and work very well in space.
Rockets for military and recreational uses date back to at least 13th
century China.
Significant scientific, interplanetary and industrial use did not occur
until the 20th century, when rocketry was the enabling technology of
the Space
Age, including setting foot on the moon. Rockets are now used for
fireworks,
weaponry,
ejection seats, launch vehicles for artificial satellites,
human spaceflight, and space exploration.
Chemical rockets are the
most common type of rocket and they typically create their exhaust by
the combustion of rocket propellant. Chemical rockets store a large amount
of energy in an easily released form, and can be very dangerous.
However, careful design, testing, construction and use minimizes risks.
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