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Rockets
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 parachute landing immediately
before touchdown (see Soyuz spacecraft).
Most current rockets
are chemically powered rockets (internal combustion
engines). 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.
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