| A rocket is a vehicle, missile or
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| | board the UK-DMC satellite. There are
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| aircraft which obtains thrust by the
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| | even proposals to use steam rockets for
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| reaction to the ejection of fast moving
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| | interplanetary transport using either
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| fluid from within a rocket engine.
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| | nuclear or solar heating as the power
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| Overview
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| | source to vaporize water collected from
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| Uses
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| | around the solar system.
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| In military use, rockets generally use
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| | Rockets where the heat is supplied from
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| solid propellant and are unguided.
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| | other than the propellant, such as steam
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| Rockets equipped with warheads
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| | rockets, are classed as external
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| (representing a form of missile) can be
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| | combustion engines. Other examples of
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| fired by ground-attack aircraft at fixed
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| | external combustion rocket engines
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| targets such as buildings, or can be
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| | include most designs for nuclear powered
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| launched by ground forces at other ground
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| | rocket engines. Use of hydrogen as the
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| targets. During the Vietnam era, there
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| | propellant for external combustion
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| were also air-launched unguided rockets
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| | engines gives very high velocities.
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| that carried a nuclear payload designed
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| | Rockets must be used when there is no
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| to attack aircraft formations in flight.
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| | other substance (land, water, or air) or
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| In military terminology, the word missile
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| | force (gravity, magnetism, light) that a
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| is often preferred over rocket when the
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| | vehicle may employ for propulsion, such
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| weapon uses either solid or liquid
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| | as in space. In these circumstances, it
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| propellant, and has a guidance system.
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| | is necessary to carry all the propellant
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| (This distinction generally does not
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| | to be used.
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| apply to civilian or orbital launch
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| | Delta-v
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| vehicles.)
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| | Delta-v is the theoretical total gain in
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| Rockets remain the only way to leave the
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| | speed that a rocket can achieve without
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| Earth and are used to launch into orbit,
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| | any external interference (without air
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| to rapidly accelerate vehicles, to change
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| | drag or gravity or other forces).
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| orbits, to de-orbit for landing, or for
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| | Due to their high exhaust velocity (mach
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| landing especially if there is no
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| | ~10+), rockets are particularly useful
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| atmosphere, e.g., for landing on the
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| | when very high speeds are required, such
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| Moon, and sometimes to soften a hard
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| | as orbital speed (mach 25). The speeds
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| parachute landing immediately before
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| | that a rocket vehicle can reach can be
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| touchdown (see Soyuz spacecraft).
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| | calculated by the rocket equation; which
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| Operation
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| | gives the speed difference ("delta-v") in
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| In all rockets, the exhaust is formed
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| | terms of the exhaust speed and ratio of
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| from propellant, which is carried within
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| | initial mass to final mass ("mass
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| the rocket prior to its release. Rocket
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| | ratio").
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| thrust is due to the action of
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| | The mass ratios that can be achieved with
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| accelerating the exhaust to very high
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| | a single set of fixed rocket engines and
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| speeds causing an equal and opposite
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| | tankage varies depends on acceleration
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| reaction on the vehicle.
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| | required, construction materials, tank
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| Types
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| | layout, engine type and propellants used,
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| There are many different types of
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| | but for example the first stage of the
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| rockets, and a comprehensive list can be
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| | Saturn V was able to achieved about a
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| found in rocket engine — they
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| | mass ratio of 10.
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| range in size from tiny models such as
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| | Staging
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| water rockets or small solid rockets that
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| | Often, the required velocity (delta-v)
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| can be purchased at a hobby store, to the
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| | for a mission is unattainable by any
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| enormous Saturn V used for the Apollo
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| | single rocket because the propellant,
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| program.
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| | structure, guidance and engines weigh so
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| Most current rockets are chemically
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| | much as to prevent the mass ratio from
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| powered rockets (internal combustion
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| | being high enough.
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| engines) that emit a hot exhaust gas. A
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| | This problem is frequently solved by
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| chemical rocket engine can use solid
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| | staging — the rocket sheds excess
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| propellant (see Space Shuttle's SRBs),
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| | weight (usually tankage and engines)
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| liquid propellant (see Space shuttle main
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| | during launch to reduce its weight and
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| engine), or a hybrid mixture of both. A
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| | effectively increase its mass ratio.
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| chemical reaction is initiated between
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| | Typically, the acceleration of a rocket
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| the fuel and the oxidizer in the
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| | increases with time (if the thrust stays
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| combustion chamber, and the resultant hot
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| | the same) as the weight of the rocket
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| gases accelerate out of a nozzle (or
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| | decreases as propellant is burned.
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| nozzles) at the rearward-facing end of
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| | Discontinuities in acceleration will
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| the rocket. The acceleration of these
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| | occur when stages burn out, often
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| gases through the engine exerts force
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| | starting at a lower acceleration with
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| ("thrust") on the combustion chamber and
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| | each new stage firing.
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| nozzle, propelling the vehicle (in
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| | Vehicles
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| accordance with Newton's Third Law). See
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| | Rockets as a group have the highest
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| rocket engine for details.
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| | thrust/weight ratio of any type of
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| Not all rockets use chemical reactions.
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| | engine; and this helps vehicles achieve a
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| Steam rockets, for example, release
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| | high mass ratios, which improves the
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| superheated water through a nozzle where
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| | performance of flight.
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| it instantly flashes to high velocity
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| | Common mass ratios for vehicles are 20:1
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| steam, propelling the rocket. The
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| | for dense propellants such as liquid
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| efficiency of steam as a rocket
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| | oxygen and kerosene, 25:1 for dense
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| propellant is relatively low, but it is
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| | monopropellants such as hydrogen
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| simple and reasonably safe, and the
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| | peroxide, and 10:1 for liquid oxygen and
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| propellant is cheap and widely available.
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| | liquid hydrogen. However, mass ratio is
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| Most steam rockets have been used for
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| | highly dependent on many factors such as
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| propelling land-based vehicles but a
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| | the type of engine the vehicle uses and
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| small steam rocket was tested in 2004 on
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| | structural safety margins
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