Rockets, What You Should Know

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Rockets, What You Should Know

• Mr. Lewis
• Music, Motion Multimedia, 2007

Information from http//www.qrg.northwestern.edu/p
rojects/vss/docs/Propulsion/1-how-are-rockets-desi
gned.html
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Blast Off!

• To understand more about rockets, one needs to
  understand physics.

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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.

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Sir Isaac Newton
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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Every Action has an Equal and Opposite Reaction?

• This is the 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.

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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.

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Every Action has an Equal and Opposite Reaction?
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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.

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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.

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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.

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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.

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Is there gravity in space?

• There is gravity 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.

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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.

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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.

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Is there gravity in space?
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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.

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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.

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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.

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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 extraterrestrial?) -made.

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What is an orbit?

• In our solar 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.

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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

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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!

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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."

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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.

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How can something as small as an atom move a
space craft?

• Anything with a 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.

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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!