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Rockets What You Should Know

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					 Rockets, What You Should
 Know




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
 extraterrestrial?) -made.
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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