Exploring the Universe
 

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Article #1: How rockets work

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One of the most amazing endeavors man has This concept of "throwing mass and
ever undertaken is the exploration of benefiting from the reaction" can be hard
space. A big part of the amazement is the to grasp at first, because that does not
complexity. Space exploration is seem to be what is happening. Rocket
complicated because there are so many engines seem to be about flames and noise
problems to solve and obstacles to and pressure, not "throwing things."
overcome. You have things like: Let's look at a few examples to get a
The vacuum of space better picture of reality:
Heat management problems If you have ever shot a shotgun,
The difficulty of re-entry especially a big 12-gauge shot gun, then
Orbital mechanics you know that it has a lot of "kick."
Micrometeorites and space debris That is, when you shoot the gun it
Cosmic and solar radiation "kicks" your shoulder back with a great
The logistics of having restroom deal of force. That kick is a reaction. A
facilities in a weightless environment shotgun is shooting about an ounce of
But the biggest problem of all is metal in one direction at about 700 miles
harnessing enough energy simply to get a per hour, and your shoulder gets hit with
spaceship off the ground. That is where the reaction. If you were wearing roller
rocket engines come in. skates or standing on a skateboard when
Rocket engines are, on the one hand, so you shot the gun, then the gun would be
simple that you can build and fly your acting like a rocket engine and you would
own model rockets very inexpensively (see react by rolling in the opposite
the links on the last page of the article direction.
for details). On the other hand, rocket If you have ever seen a big fire hose
engines (and their fuel systems) are so spraying water, you may have noticed that
complicated that only three countries it takes a lot of strength to hold the
have actually ever put people in orbit. hose (sometimes you will see two or three
In this article, we will look at rocket firefighters holding the hose). The hose
engines to understand how they work, as is acting like a rocket engine. The hose
well as to understand some of the is throwing water in one direction, and
complexity surrounding them. the firefighters are using their strength
When most people think about motors or and weight to counteract the reaction. If
engines, they think about rotation. For they were to let go of the hose, it would
example, a reciprocating gasoline engine thrash around with tremendous force. If
in a car produces rotational energy to the firefighters were all standing on
drive the wheels. An electric motor skateboards, the hose would propel them
produces rotational energy to drive a fan backwards at great speed!
or spin a disk. A steam engine is used to When you blow up a balloon and let it go
do the same thing, as is a steam turbine so that it flies all over the room before
and most gas turbines. running out of air, you have created a
Rocket engines are fundamentally rocket engine. In this case, what is
different. Rocket engines are reaction being thrown is the air molecules inside
engines. The basic principle driving a the balloon. Many people believe that air
rocket engine is the famous Newtonian molecules don't weigh anything, but they
principle that "to every action there is do (see the page on helium to get a
an equal and opposite reaction." A rocket better picture of the weight of air).
engine is throwing mass in one direction When you throw them out the nozzle of a
and benefiting from the reaction that balloon, the rest of the balloon reacts
occurs in the other direction as a in the opposite direction.
result.






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