# Rockets What You Should Know

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```					 Rockets, What You Should
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Information from http://www.qrg.northwestern.edu/projects/vss/docs/Propulsion/1-how-are-rockets-designed.html
Blast Off!
 To understand moreabout rockets, one
needs to understand physics.
Sir Isaac Newton
   Sir Isaac Newton (4 January 1643 – 31
March 1727) was an English physicist,
mathematician, astronomer, natural
philosopher, and alchemist, regarded by
many as the greatest figure in the history of
science.[2] His treatise Philosophiae Naturalis
Principia Mathematica, published in 1687,
described universal gravitation and the three
laws of motion, laying the groundwork for
classical mechanics.
Sir Isaac Newton
Inertia
 Inertia (the property of matter by which it
retains its state of rest or its velocity
along a straight line so long as it is not
acted upon by an external force) is a word
we use when we talk about matter and
movement. Velocity is in mechanics is the
time rate of change of position of a body
in a specified direction.
 Basically, our idea of inertia goes back to Sir
Isaac Newton's first two laws of physics:

1. An object at rest tends to stay at rest.
2. An object in motion tends to stay in
motion.
Inertia
 Inertia  is a object's reluctance to
change its state of motion: From a state
of rest to motion or vice versa.
 Matter is anything you can touch.
Inertia
 If you want to overcome inertia, you
have to apply a force. A force will make
something that is still start to move, like
flicking a wad of paper with a pencil will
make it move. Also force, due to
resistance, will slow or stop something
that is already moving. The wad of
paper will be slowed by resistance
made by rubbing up against the air it is
passing through.
What is mass?
   We use the word mass to talk about how
much matter there is in something. (Matter is
anything you can touch physically.) On Earth,
we weigh things to figure out how much mass
there is. The more matter there is, the more
something will weigh. Often, the amount of
mass something has is related to its size, but
not always. A balloon blown up bigger than
your head will still have less matter inside it
than your head (for most people, anyhow)
and therefore less mass.
What is mass?
   The difference between mass and weight is
that weight is determined by how much
something is pulled by gravity. If we are
comparing two different things to each other
on Earth, they are pulled the same by gravity
and so the one with more mass weighs more.
But in space, where the pull of gravity is very
small, something can have almost no weight.
It still has matter in it, though, so it still has
mass.
Why is mass important?
   Mass is important because of two major
factors affecting how things move in space:
inertia and gravity. The more mass something
has, the more of both it experiences. That is
why heavy things (things with a lot of mass)
are hard to move. When an object is sitting
still, it resists moving, and the more mass it
has the more it resists. The amount of thrust
needed to move something and how fast it
ends up moving are both directly tied to its
mass.
Why is mass important?
 On   the other hand, once something
massive starts moving, it is very hard to
stop. This is also due to the relationship
between mass and inertia.
 Gravity is also proportional to how much
mass each thing has. The bigger an
object is, the larger the gravitational pull
it exerts.
Why is mass important?
 Because of  gravity and inertia, the more
massive something is, the harder it is to
get into space, the harder it is to keep it
there, and the harder it is to move it
where you want it to go when it is there.
For that reason, a lightweight spacecraft
is better than heavy spacecraft.
Every Action has an Equal
and Opposite Reaction?
 This isthe third of Sir Isaac Newton's
laws of physics, and one that is very
important to space flight. Here's how it
works. If you push on anything, it
pushes back on you. That's why if you
lean against the wall, you don't just fall
through it.
Every Action has an Equal
and Opposite Reaction?
   The wall pushes back on you as hard as you
push on it, and you and the wall stay in place.
If you throw something, you put more force
behind it than just leaning on it, so it pushes
back with more force. This is hard to observe,
because usually, if you throw something
away from you, the friction between you and
the floor makes resistance to keep you in
place.
Every Action has an Equal
and Opposite Reaction?
Every Action has an Equal
and Opposite Reaction?
 If you take away the friction and try again, you
will move away from the thing you threw as
much as it moves away from you.
 The bigger the push, the bigger the push
back. That's why cannons and guns recoil. As
the cannon ball flies on one direction, the
cannon moves in the opposite direction. If we
turn the cannon up on end, it gets a little
closer to how a rocket works. The force that
pushes the cannon ball down also pushes the
cannon up. But since the cannon is bigger
than the cannon ball it has more inertia acting
to keep it in one place.
What is gravity?
 Gravity is a force pulling together all
matter (which is anything you can
physically touch). The more matter, the
more gravity, so things that have a lot of
matter such as planets and moons and
stars pull more strongly.
What is gravity?
   Mass is how we measure the amount of
matter in something. The more massive
something is, the more of a gravitational pull
it exerts. As we walk on the surface of the
Earth, it pulls on us, and we pull back. But
since the Earth is so much more massive
than we are, the pull from us is not strong
enough to move the Earth, while the pull from
the Earth can make us fall flat on our faces.
What is gravity?
 In addition to depending on the amount
of mass, gravity also depends on how
far you are from something. This is why
we are stuck to the surface of the Earth
instead of being pulled off into the Sun,
which has many more times the gravity
of the Earth.
Is there gravity in space?
 There isgravity everywhere. It gives
shape to the orbits of the planets, the
solar system, and even galaxies.
Gravity from the Sun reaches
throughout the solar system and
beyond, keeping the planets in their
orbits. Gravity from Earth keeps the
Moon and human-made satellites in
orbit.
Is there gravity in space?
   It is true that gravity decreases with distance,
so it is possible to be far away from a planet
or star and feel less gravity. But that doesn't
account for the weightless feeling that
astronauts experience in space. The reason
that astronauts feel weightless actually has to
do with their position compared to their
spaceship. We feel weight on Earth because
gravity is pulling us down, while the floor or
ground stop us from falling.
Is there gravity in space?
 We are  pressed against it. Any ship in
orbit around the Earth is falling slowly to
Earth. Since the ship and the astronauts
are falling at the same speed, the
astronauts don't press against anything,
so they feel weightless.
Is there gravity in space?
Is there gravity in space?
    You can feel something very like what
the astronauts feel for a moment in a
fast-moving elevator going down or in a
roller coaster, when you start going
down a big hill. You are going down
rapidly, but so is the roller coaster or the
elevator so for a second you feel
weightless.
How do objects travel in
space?
   Objects in space follow the laws or rules of
physics, just like objects on Earth do. Things
in space have inertia. That is, they travel in a
straight line unless there is a force that makes
them stop or change. The movement of
things in space is influenced by gravity.
Gravity is an important force that can change
the course of bodies in space or pull them off
of one course, or even cause them to crash
together.
How do objects travel in
space?
 While some objects in   space travel in
irregular paths, most (especially our
near neighbors in space) tend to travel
in orbits around the Sun or around
planets. The orbits are usually close to
circular, but are actually slightly
flattened ellipses.
What is an orbit?
 An orbit is a regular, repeating path that
an object in space takes around another
one. An object in an orbit is called a
satellite. A satellite can be natural, like
the moon, or human (or
What is an orbit?
 In oursolar system, the Earth orbits the
Sun, as do the other seven planets.
They all travel on or near the orbital
plane, an imaginary disk-shaped
surface in space. All of the orbits are
circular or elliptical in their shape. In
addition to the planets' orbits, many
planets have moons which are in orbit
around them.
How are rockets designed?
 Rocket designers want the rocket to do the
best job possible for its mission. The
performance of rocket engines can be
measured in several ways, and the designer
must decide which kinds of performance he
or she would like the rocket to emphasize.
 Some important questions for rocket engine
designers are the following:
How are rockets designed?
 How   powerful is the rocket; how
much thrust can the motor produce?
This is important because the rocket
must be powerful enough to counteract
Earth's gravity, and get its payload (the
stuff that the spacecraft is carrying) into
orbit, or even out of orbit!
How are rockets designed?
   What is the power-to-weight ratio? This is
important because the heavier the engine is,
the harder it will be to get the spacecraft into
space. However bigger (heavier) engines can
be much stronger than small light ones. If you
make a light enough spacecraft, it may not
have enough thrust. So if a rocket is heavy, it
must be strong, and if it is weak, it should be
light.
How are rockets designed?
 What is the speed of the exhaust gases?
The faster the exhaust gasses stream out, the
more thrust, and thus the faster the ship goes
forward.
 How long can it run? The rocket has to get
its payload to its destination against gravity. If
the rocket runs out of oomph too quickly, the
rocket may fall back to Earth or put its
payload into a completely wrong orbit.
How are rockets designed?
   No rocket design or kind of propellant will
give the best answer to all of these questions.
There are always tradeoffs; depending on
what the satellite needs different kinds of
rockets are chosen. The designer must
choose which qualities are most important to
his or her design and this changes depending
on the rocket's intended purpose. Sometimes
a single mission will have more than one
propulsion system for different kinds of
propulsion.
Types of Propellants
 The solid motor is used mainly as a
booster for launch vehicles. Solid
motors are almost never used in space
because they are not controllable. The
boosters are lit and then they fire until
all the propellant has burned. Their
main benefits are simplicity, a shelf life
which can extend to years as in the
case of missiles, and high reliability.
Types of Propellants
   Liquid motors come in many shapes and
sizes: Most of them are controllable (can be
throttled up and down), restart-able, are often
used as control and maneuvering thrusters.
Liquid thrusters can be broken into three
main types: monopropellant, bipropellant, and
cryogenic thrusters. Monopropellants only
use one propellant such as hydrazine.
Bipropellants use a fuel and an oxidizer such
as RP-1 and H2O2.
Types of Propellants
   Liquid Motors Continued: Cryogenic systems
use liquefied gases such as LiH and LOX
(liquid hydrogen and liquid oxygen).
Cryogenic means super-cooled. You would
have to super-cool hydrogen and oxygen to
make them liquids. With each step from
monopropellant to bipropellant to cryogenic
the thruster complexity goes up but the
performance also goes up.
Types of Propellants
 Cold-gas motors     have controllability
similar to liquids but are the simpler and
lighter. They are basically a high
pressure tank with switches which flip
between the open and shut state. They
function a little like spray paint, with the
contents under pressure inside, and
when the valve is opened, they stream
out.
Types of Propellants
 Ion engines are vastly different from
chemical (solid, liquid) engines in that
they are low thrust engines which can
run for extended periods of time. The
length of use of chemical engines is
usually from seconds to days while the
length of use of ion engines can be
anywhere from days to months.
How does propulsion work?
   Propulsion moves things like spacecraft or jet
planes forward by pushing something out of
the back. Think of a balloon that you blow up
and then release. The air rushing out of the
back pushes the balloon forward. This
happens because of a phenomenon
described by Sir Issac Newton: "every action
has an equal and opposite reaction."
Every Action has an Equal
and Opposite Reaction?
   We would need a larger force to push the
cannon a great distance. If we could make a
long continuous hot explosion in the cannon,
instead of one quick one, we could push the
cannon a far distance. The air that is heated
would push out the back, pushing the cannon
in the opposite direction. This is how jets work
as well as how rockets get into space.
Remember, because every action has an
equal and opposite reaction something will go
forward if it is pushing matter behind itself.
How can something as
small as an atom move a
space craft?
 Anything witha propulsion system
works when something (usually a gas--
sometimes a liquid) pushes out of it.
This makes thrust. Any gas or liquid is
made of atoms, so jet engines, the
space shuttle, and Fourth of July
fireworks are all pushed forward by
atoms shooting out of them.
How can something as
small as an atom move a
space craft?
   Everything from fireworks to space shuttles
are moved by atoms. There are two important
factors: how many atoms are being used and
how fast they are going. In space shuttle
launches, the fuel flow rate at launch is about
10 tons a second. This means that for each
second of the launch a space shuttle burns
10 tons of fuel. That's a huge amount of
atoms!

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