How Rockets Work 

Gravity is a force that pulls things back to the ground. In 
space it can pull things together, like the earth, sun, and the 
moon. It keeps people, animals, buildings, and trees firmly in 
place and prevents our atmosphere from drifting off into space. 
As beneficial as it is to man's survival, however, it also 
makes escape from earth very difficult.  

To escape the gravitational field that 
surrounds the earth, you must travel very fast, roughly 20,000
 m.p.h. That's about twenty times the speed of the Concorde!

The only engines that can give a space ship the speed it 
needs to reach and function in space are rockets. Jet
engines won't work because they take oxygen from the air 
to make their fuel burn. 

In space, there is no oxygen.  
Rocket engines carry their own oxygen, often in liquid form.
Such a large amount of this rocket fuel is needed,
in fact, that 9/10 of the total weight of some rockets 
is fuel.

Rockets work very simply.  The fuel in the engines makes
hot gases. These gases rush out the end of the rocket and
create thrust.  This thrust pushes the rocket forward. 
It is similar to what happens when you blow up a balloon
and then allow the air to escape out the end. If you let go
of the balloon, it will be propelled forward until it runs 
out of air.

Russian rocket to be used to transport equipment to International Space Station

If a rocket needs extra power, it uses boosters.  These are
small, extra rockets strapped to the side of the main rocket. 
When their fuel is gone, they separate and fall away. 

 rocket links

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    Gemini take off                       Saturn V rocket on display      

Until the shuttle, rockets were used only once, as the rockets 
and boosters were destroyed after takeoff.