Rockets 1 Rockets

Rockets 2 Introductory Question If there were no launch pad beneath the space shuttle at lift-off, the upward thrust of its engines would be If there were no launch pad beneath the space shuttle at lift-off, the upward thrust of its engines would be A. approximately unchanged. B. approximately half as much. C. approximately zero.

Rockets 3 Observations about Rockets Plumes of flame emerge from rockets Plumes of flame emerge from rockets Rockets can accelerate straight up Rockets can accelerate straight up Rockets can go very fast Rockets can go very fast The flame only touches the ground initially The flame only touches the ground initially Rockets can apparently operate in empty space Rockets can apparently operate in empty space Rockets usually fly nose-first Rockets usually fly nose-first

Rockets 4 6 Questions about Rockets What pushes a rocket forward? What pushes a rocket forward? How does the rocket use its gas to obtain thrust? How does the rocket use its gas to obtain thrust? What keeps a rocket pointing forward? What keeps a rocket pointing forward? What limits a rocket’s speed, if anything? What limits a rocket’s speed, if anything? Once in space, does a spaceship have a weight? Once in space, does a spaceship have a weight? What makes a spaceship orbit the earth? What makes a spaceship orbit the earth?

Rockets 5 Question 1 What pushes a rocket forward? What pushes a rocket forward?

Rockets 6 Momentum Conservation A rocket’s momentum is initially zero A rocket’s momentum is initially zero That momentum is redistributed during thrust That momentum is redistributed during thrust Ship pushes on fuel; fuel pushes on ship Ship pushes on fuel; fuel pushes on ship Fuel acquires backward momentum Fuel acquires backward momentum Ship acquires forward momentum Ship acquires forward momentum Rocket’s total momentum remains zero Rocket’s total momentum remains zero

Rockets 7 Rocket Propulsion Neglecting gravity, then Neglecting gravity, then rocket’s total momentum is always zero rocket’s total momentum is always zero momentum fuel + momentum ship = 0 The momenta of ship and fuel are opposite The momenta of ship and fuel are opposite The ship’s momentum is equal but opposite to The ship’s momentum is equal but opposite to the velocity of the fuel the velocity of the fuel times the mass of that fuel times the mass of that fuel

Rockets 8 Introductory Question (revisited) If there were no launch pad beneath the space shuttle at lift-off, the upward thrust of its engines would be If there were no launch pad beneath the space shuttle at lift-off, the upward thrust of its engines would be A. approximately unchanged. B. approximately half as much. C. approximately zero.

Rockets 9 Question 2 How does the rocket use its gas to obtain thrust? How does the rocket use its gas to obtain thrust?

Rockets 10 Rocket Engines Combustion produces hot, high-pressure gas Combustion produces hot, high-pressure gas The gas speeds up in a de Laval nozzle The gas speeds up in a de Laval nozzle Gas reaches sonic speed in the nozzle’s throat Gas reaches sonic speed in the nozzle’s throat Beyond the throat, supersonic gas expands to speed up further Beyond the throat, supersonic gas expands to speed up further

Rockets 11 Question 3 What keeps a rocket pointing forward? What keeps a rocket pointing forward?

Rockets 12 Stability and Orientation On the ground, a rocket needs static stability On the ground, a rocket needs static stability In the air, a rocket needs aerodynamic stability In the air, a rocket needs aerodynamic stability Center of aerodynamic forces behind center of mass Center of aerodynamic forces behind center of mass In space, a spaceship is a freely rotating object In space, a spaceship is a freely rotating object Orientation governed by angular momentum Orientation governed by angular momentum Small rockets are used to exert torques on spaceship Small rockets are used to exert torques on spaceship Spaceship’s orientation doesn’t affect its travel Spaceship’s orientation doesn’t affect its travel

Rockets 13 Question 4 What limits a rocket’s speed, if anything? What limits a rocket’s speed, if anything?

Rockets 14 Ship’s Ultimate Speed Increases as Increases as the ratio of fuel mass to ship mass increases the ratio of fuel mass to ship mass increases the fuel exhaust speed increases the fuel exhaust speed increases If fuel were released with the rocket at rest, If fuel were released with the rocket at rest, Because rocket accelerates during thrust, ultimate speed is less than given above Because rocket accelerates during thrust, ultimate speed is less than given above

Rockets 15 Question 5 Once in space, does a spaceship have a weight? Once in space, does a spaceship have a weight?

Rockets 16 Gravity (Part 1) The earth’s acceleration due to gravity is only constant for small changes in height The earth’s acceleration due to gravity is only constant for small changes in height When the distance between two objects changes substantially, the relationship is: When the distance between two objects changes substantially, the relationship is:

Rockets 17 Gravity (Part 2) The ship’s weight is only constant for small changes in height The ship’s weight is only constant for small changes in height When the ship’s height changes significantly: When the ship’s height changes significantly:

Rockets 18 Gravity (Part 3) Even far above earth, an object has weight Even far above earth, an object has weight Astronauts and spaceships have weights Astronauts and spaceships have weights weights are somewhat less than normal weights are somewhat less than normal weights depend on altitude weights depend on altitude Astronauts and spaceships are in free fall Astronauts and spaceships are in free fall Astronauts feel weightless because they are falling Astronauts feel weightless because they are falling

Rockets 19 Question 6 What makes a spaceship orbit the earth? What makes a spaceship orbit the earth?

Rockets 20 Orbits (Part 1) An object that begins to fall from rest falls directly toward the earth An object that begins to fall from rest falls directly toward the earth Acceleration and velocity are in the same direction Acceleration and velocity are in the same direction

Rockets 21 Orbits (Part 2) An object that has a sideways velocity follows a trajectory called an orbit An object that has a sideways velocity follows a trajectory called an orbit Orbits can be closed or open, and are ellipses, parabolas, and hyperbolas Orbits can be closed or open, and are ellipses, parabolas, and hyperbolas

Rockets 22 Current Rocket Technology X-Prize Rockets X-Prize Rockets Single State to Orbit Rockets Single State to Orbit Rockets Improbable Dreams Improbable Dreams Rockets that rarely require refueling Rockets that rarely require refueling Rockets that can land and leave large planets Rockets that can land and leave large planets Rockets that can turn on a dime in space Rockets that can turn on a dime in space

Rockets 23 Summary About Rockets Rockets are pushed forward by their fuel Rockets are pushed forward by their fuel Total rocket impulse is basically the product of exhaust speed times exhaust mass Total rocket impulse is basically the product of exhaust speed times exhaust mass Rockets can be stabilized aerodynamical Rockets can be stabilized aerodynamical Rockets can be stabilized by thrust alone Rockets can be stabilized by thrust alone After engine burn-out, spaceships can orbit After engine burn-out, spaceships can orbit