There are four major
components
to any full scale rocket; the
structural system,
or frame, the
payload system, the
guidance system, and the
propulsion system.
The propulsion of a rocket includes all of the
parts which make up the rocket engine; the tanks
pumps, propellants, power head, and rocket nozzle .
The function of the propulsion system
is to produce thrust.
Thrust is the force which moves a
rocket through the air and through space. Thrust is generated by the
propulsion system
of the rocket. Different propulsion systems develop thrust in
different ways, but all thrust is generated through some
application of Newton's third law of
motion. For every action there is an equal and opposite reaction.
In any propulsion system, a working fluid is
accelerated by the system and
the reaction to this acceleration produces a force on the system. A
general derivation of the thrust equation
shows that the amount of thrust generated depends on the
mass flow
through the engine and the
exit velocity
of the gas.
In a rocket engine , fuel and
a source of oxygen, called an oxidizer, are mixed and exploded
in a combustion chamber. The
combustion
produces hot exhaust which is passed through a
nozzle
to accelerate the flow and
produce thrust.
For a rocket, the accelerated gas, or
working fluid, is the hot exhaust produced during combustion.
This is a different working fluid than you find in a
gas turbine engine
or propeller powered aircraft.
Turbine engines and
propellers use air from the atmosphere as the working fluid,
but rockets use the combustion exhaust gases.
In outer space there is no atmosphere so turbines and propellers
can not work there.
This explains why a rocket works in space
but a turbine engine or a propeller does not work.
There are two main categories of rocket engines; liquid rockets and
solid rockets. In a
liquid rocket,
the propellants, the fuel and the oxidizer,
are stored separately as liquids and are pumped into
the combustion chamber of the nozzle
where burning occurs. In a
solid rocket,
the propellants are mixed together
and packed into a solid cylinder. Under normal temperature conditions,
the propellants do not burn; but they will burn when exposed to
a source of heat provided by an igniter.
Once the burning starts,
it proceeds until all the propellant is exhausted.
With a liquid rocket, you can stop the thrust by turning off the flow of
propellants; but with a solid rocket, you have to destroy the casing to stop
the engine. Liquid rockets tend to be heavier and more
complex because of the pumps and storage tanks. The propellants are
loaded into the rocket just before launch.
A solid rocket is much easier to handle and can sit for years
before firing.
On this slide, we show a picture of a Saturn 1B
at the left and a picture of a rocket engine test at
the right. For the picture at the right, we only see the
outside of the rocket nozzle, with the hot gas exiting out the
bottom. The
first stage of the
Saturn 1B was powered by eight liquid rocket engines burning
a hydrocarbon fuel with liquid oxygen. The second stage used
a single liquid hydrogen and liquid oxygen powered engine and
was used to place the Apollo spacecraft into low earth orbit.
Guided Tours
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Rocket Systems:
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Propulsion System:
-
Full Scale Rockets:
Activities:
Rocket Propulsion Activity: Grade 9-10
Related Sites:
Rocket Index
Rocket Home
Beginner's Guide Home
