1. Traveling to Space
Flight and Space
© 2011 Project Lead The Way, Inc.

2. Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Why Do We Use Rockets?
Rockets provide high speed, high power transportation both within the Earth’s atmosphere and in space.
Military use
Atmospheric research
Launching probes and satellites
Space travel
Fireworks
A rocket is a type of engine that pushes itself forward or upward by producing thrust. Unlike a jet engine, which draws in outside air, a rocket engine uses only the substances carried within it. As a result, a rocket can operate in outer space, where there is almost no air. A rocket can produce more power for its size than any other kind of engine. For example, the main rocket engine of the space shuttle weighs only a fraction as much as a train engine, but it would take 39 train engines to produce the same amount of power. The word rocket can also mean a vehicle or object driven by a rocket engine. Rockets come in a variety of sizes. Some rockets that shoot fireworks into the sky measure less than 2 feet (60 centimeters) long. Rockets 50 to 100 feet (15 to 30 meters) long serve as long-range missiles that can be used to bomb distant targets during wartime. Larger and more powerful rockets lift spacecraft, artificial satellites, and scientific probes into space. For example, the Saturn 5 rocket that carried astronauts to the moon stood about 363 feet (111 meters) tall.
Rocket engines generate thrust by expelling gas. Most rockets produce thrust by burning a mixture of fuel and an oxidizer, a substance that enables the fuel to burn without drawing in outside air. This kind of rocket is called a chemical rocket because burning fuel is a chemical reaction. The fuel and oxidizer are called the propellants.
A chemical rocket can produce great power, but it burns propellants rapidly. As a result, it needs a large amount of propellants to work for even a short time. The Saturn 5 rocket burned more than 560,000 gallons (2,120,000 liters) of propellants during the first 2 3/4 minutes of flight. Chemical rocket engines become extremely hot as the propellants burn. The temperature in some engines reaches 6000 degrees F (3300 degrees C), much higher than the temperature at which steel melts.
Jet engines also burn fuel to generate thrust. Unlike rocket engines, however, jet engines work by drawing in oxygen from the surrounding air.
Researchers have also developed rockets that do not burn propellants. Nuclear rockets use heat generated by a nuclear fuel to produce thrust. In an electric rocket, electric energy produces thrust.
Military forces have used rockets in war for hundreds of years. In the 1200s, Chinese soldiers fired rockets against attacking armies. British troops used rockets to attack Fort McHenry in Maryland during the War of 1812 ( ). After watching the battle, the American lawyer Francis Scott Key described "the rocket's red glare" in the song "The Star-Spangled Banner." During World War I ( ), the French used rockets to shoot down enemy observation balloons. Germany attacked London with V-2 rockets during World War II ( ). In the Persian Gulf War of 1991 and the Iraq War, which began in 2003, United States troops launched rocket-powered Patriot missiles to intercept and destroy Iraqi missiles.
Rockets are the only vehicles powerful enough to carry people and equipment into space. Since 1957, rockets have lifted hundreds of artificial satellites into orbit around Earth. These satellites take pictures of Earth's weather, gather information for scientific study, and transmit communications around the world. Rockets also carry scientific instruments far into space to explore and study other planets. Since 1961, rockets have launched spacecraft carrying astronauts and cosmonauts into orbit around Earth. In 1969, rockets carried astronauts to the first landing on the moon. In 1981, rockets lifted the first space shuttle into Earth orbit.

3. How Does a Rocket Work? How Does A Rocket Work? Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
How Does a Rocket Work?
How Does A Rocket Work?
Make sure you are connected to the Internet and click on the “How Does a Rocket Work?” hyperlink.
Rocket engines generate thrust by putting a gas under pressure. The pressure forces the gas out the end of the rocket. The gas escaping the rocket is called exhaust. As it escapes, the exhaust produces thrust according to the laws of motion defined by the English scientist Isaac Newton. Newton's third law of motion states that for every action, there is an equal and opposite reaction. Thus, as the rocket pushes the exhaust backward, the exhaust pushes the rocket forward.
The amount of thrust produced by a rocket depends on the momentum of the exhaust – that is, its total amount of motion. The exhaust's momentum equals its mass (amount of matter) multiplied by the speed at which it exits the rocket. The more momentum the exhaust has, the more thrust the rocket produces. Engineers can therefore increase a rocket's thrust by increasing the mass of exhaust it produces. Alternately, they can increase the thrust by increasing the speed at which the exhaust leaves the rocket.

4. Model Rockets vs. Real Rockets
Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
4 forces throughout flight
All of flight in atmosphere; aerodynamics very important
Very short powered flight
Solid rocket engine
Passive stability; no control
Low speed; heating not important
Inexpensive materials: balsa, cardboard, plastic
4 forces during atmospheric flight
Short time in atmosphere; aerodynamics less important
Long powered flight
Liquid or solid rocket engine
Passive stability; active control
High speed; heating important
Expensive materials: aluminum, titanium, nickel alloy

5. Parts of a Model Rocket Traveling to Space PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Parts of a Model Rocket
Beginning at the far right, the body of the rocket is a green cardboard tube with black fins attached at the rear. The fins can be made of either plastic or balsa wood and are used to provide stability during flight. Model rockets use small, pre-packaged, solid fuel engines. The engine is used only once and then is replaced with a new engine for the next flight. Engines come in a variety of sizes and can be purchased at hobby stores and at some toy stores. The thrust of the engine is transmitted to the body of the rocket through the engine mount. This part is fixed to the rocket and can be made of heavy cardboard or wood. There is a hole through the engine mount to allow the ejection charge of the engine to pressurize the body tube at the end of the coasting phase and eject the nose cone and the recovery system. Recovery wadding is inserted between the engine mount and the recovery system to prevent the hot gas of the ejection charge from damaging the recovery system. The recovery wadding is sold with the engine. The recovery system consists of a parachute (or a streamer) and some lines to connect the parachute to the nose cone. Parachutes and streamers are made of thin sheets of plastic. The nose cone can be made of balsa wood, or plastic, and may be either solid or hollow. The nose cone is inserted into the body tube before flight. An elastic shock cord is connected to both the body tube and the nose cone and is used to keep all the parts of the rocket together during recovery. The launch lugs are small tubes (straws) which are attached to the body tube. The launch rail is inserted through these tubes to provide stability to the rocket during launch.

6. Parts of a Real Rocket Traveling to Space PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Parts of a Real Rocket
The structural system, or frame, is similar to the fuselage of an airplane. The frame is made from very strong but lightweight materials, like titanium or aluminum, and usually employs long stringers which run from the top to the bottom which are connected to hoops and run around the circumference. The skin is then attached to the stringers and hoops to form the basic shape of the rocket. The skin may be coated with a thermal protection system to keep out the heat of air friction during flight and to keep in the cold temperatures needed for certain fuels and oxidizers. Fins are attached to some rockets at the bottom of the frame to provide stability during the flight.
The payload system of a rocket depends on the rocket's mission. The earliest payloads on rockets were fireworks for celebrating holidays. The payload of the German V2, shown in the figure, was several thousand pounds of explosives. Following World War II, many countries developed guided ballistic missiles armed with nuclear warheads for payloads. The same rockets were modified to launch satellites with a wide range of missions; communications, weather monitoring, spying, planetary exploration, and observatories, like the Hubble Space Telescope. Special rockets were developed to launch people into earth orbit and onto the surface of the Moon.
The guidance system of a rocket may include very sophisticated sensors, on-board computers, radars, and communication equipment to maneuver the rocket in flight. Many different methods have been developed to control rockets in flight. The V2 guidance system included small vanes in the exhaust of the nozzle to deflect the thrust from the engine. Modern rockets typically rotate the nozzle to maneuver the rocket. The guidance system must also provide some level of stability so that the rocket does not tumble in flight.
As you can see on the figure, most of a full scale rocket is propulsion system. There are two main classes of propulsion systems, liquid rocket engines and solid rocket engines. The V2 used a liquid rocket engine consisting of fuel and oxidizer (propellant) tanks, pumps, a combustion chamber with nozzle, and the associated plumbing. The Space Shuttle, Delta II, and Titan III all use solid rocket strap-ons.

7. Flight of a Model Rocket
Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Flight of a Model Rocket
Throughout the flight, the weight of a model rocket is fairly constant; only a small amount of solid propellant is burned relative to the weight of the rest of the rocket. This is very different from full scale rockets in which the propellant weight is a large portion of the vehicle weight. At launch , the thrust of the rocket engine is greater than the weight of the rocket and the net force accelerates the rocket away from the pad. Unlike full scale rockets, model rockets rely on aerodynamics for stability. During launch, the velocity is too small to provide sufficient stability, so a launch rail is used. Leaving the pad, the rocket begins a powered ascent. Thrust is still greater than weight, and the aerodynamic forces of lift and drag now act on the rocket. When the rocket runs out of fuel, it enters a coasting flight. The vehicle slows down under the action of the weight and drag since there is no longer any thrust present. The rocket eventually reaches some maximum altitude which you can measure using some simple length and angle measurements and trigonometry. The rocket then begins to fall back to earth under the power of gravity. While the rocket has been coasting, a delay charge has been slowly burning in the rocket engine. It produces no thrust, but may produce a small streamer of smoke which makes the rocket more easily visible from the ground. At the end of the delay charge, an ejection charge is ignited which pressurizes the body tube, blows the nose cap off, and deploys the parachute. The rocket then begins a slow descent under parachute to a recovery. The forces at work here are the weight of the vehicle and the drag of the parachute. After recovering the rocket, you can replace the engine and fly again.
On the graphic, we show the flight path as a large arc through the sky. Ideally, the flight path would be straight up and down; this provides the highest maximum altitude. But model rockets often turn into the wind during powered flight because of an effect called weather cocking. The effect is the result of aerodynamic forces on the rocket and cause the maximum altitude to be slightly less than the optimum.

8. Weather Cocking Traveling to Space PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Weather Cocking
The term weather cocking is derived from the action of a weather vane which is shown in black at the top of the figure. A weather vane is often found on the roof of a barn. It pivots about the vertical bar and always points into the wind. Older, more artistic weather vanes used the figure of a rooster with large flaring tail feathers instead of the wing shown on the figure. This type of weather vane was called a weather cock.
Why does weather cocking occur? As the rocket accelerates away from the launch pad, the velocity increases and the aerodynamic forces on the rocket increase. Aerodynamic forces depend on the square of the velocity of the air passing the vehicle. If no wind were present, the flight path would be vertical as shown at the left of the figure, and the relative air velocity would also be vertical and in a direction opposite to the flight path. If you were on the rocket, the air would appear to move past you toward the rear of the rocket.
The velocity of an object is a vector quantity having both a magnitude and a direction. When discussing velocities, we must account for both magnitude and direction. The wind introduces an additional velocity component perpendicular to the flight path, as shown in the middle of the figure. The addition of this component produces an effective flow direction shown in red on the figure. The effective flow direction is inclined to the horizontal at an angle which we shall call angle b. The size of angle b depends on the relative magnitude of the wind and the rocket velocity.

9. Flight to Orbit Traveling to Space PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Flight to Orbit

10. Orbit Traveling to Space PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Orbit
Once a launch vehicle has gotten the spacecraft out of the Earth's atmosphere, it now must enter into an orbit. An orbit is a circular or elliptical path around a celestial body (sun, star, planet, asteroid, etc.) on which an object such as a spacecraft will follow. There is a misconception that on the space shuttle and international space station there is no gravity. There is gravity acting on a person in orbit around the Earth, but they do not feel it like we feel it on Earth, because there is no ground to push back on us in space. So why doesn't a spacecraft just fall back to Earth once the rockets shut off? This is because the velocity of the spacecraft wants to move it past the Earth, while gravity pulls it back. These two actions cancel out to form an orbit. The red represents known orbit planes of Fengyun-1C debris one month after its disintegration by a Chinese interceptor. The white orbit represents the International Space Station

11. Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Orbit
Newton’s 1st Law tells us that if there is no force acting on a moving object, it will continue to move in a straight line forever.
If no force acts on a spacecraft, it will never turn and orbit a planet or moon.
The diagram above shows the path of a spacecraft if there was no gravity. In this case, the spacecraft would continue along in a straight line. Objects in space also react to forces. A spacecraft moving through the solar system is in constant motion. The spacecraft will travel in a straight line if the forces on it are in balance. This happens only when the spacecraft is very far from any large gravity source such as Earth or the other planets and their moons.

12. Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Orbit
Gravity pulls the spacecraft toward the Earth, forming a curved path. This path is known as an orbit.
If the spacecraft comes near a large body in space, the gravity of that body will unbalance the forces and curve the path of the spacecraft. This happens, in particular, when a satellite is sent by a rocket on a path that is tangent to the planned orbit about a planet. The unbalanced gravitational force causes the satellite's path to change to an arc. The arc is a combination of the satellite's fall inward toward the planet's center and its forward motion. When these two motions are just right, the shape of the satellite's path matches the shape of the body it is traveling around. Consequently, an orbit is produced. Since the gravitational force changes with height above a planet, each altitude has its own unique velocity that results in a circular orbit. Obviously, controlling velocity is extremely important for maintaining the circular orbit of the spacecraft. Unless another unbalanced force, such as friction with gas molecules in orbit or the firing of a rocket engine in the opposite direction, slows down the spacecraft, it will orbit the planet forever.
The diagram above shows the path of a spacecraft under the influence of gravity. Gravity is pulling the spacecraft toward the center of the Earth, while the velocity of the spacecraft makes the spacecraft want to keep going past the Earth. The balance of these two opposing actions is known as an orbit. For a Low Earth Orbit (LEO), which has an altitude between 600 and 2000 kilometers above the Earth's surface, the spacecraft must have a velocity of about 8 kilometers per second. That means that it can go all the way around the Earth in 90 minutes. So what happens if the spacecraft is not moving (i.e., has no velocity)? If there is no velocity, then the only force acting on the spacecraft is gravity. This means that a spacecraft would fall to Earth just as a stone falls to the ground when you drop it. So, what happens if the spacecraft is moving much faster than the 8 km/s needed to maintain a LEO? In that case, the gravity will not be able to hold the spacecraft as close to the Earth, and the spacecraft will either move into an orbit that is further away from the Earth, or if it is moving fast enough, it will escape Earth's gravity entirely. This is called the escape velocity, and it is the minimum velocity needed to escape the Earth's gravity.

13. Newton’s 2nd Law Traveling to Space PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Newton’s 2nd Law
The external force F for a rocket is a combination of the weight, thrust, drag, and lift of the vehicle. If we know the external force F, the equations can be solved to describe the motion of a rocket in flight. For some simple cases, we can write equations which describe the location and velocity of the rocket at any time in the flight. For the more general case, we can use a computer program to solve the equations. The assumption of constant mass works well for stomp rockets and fairly well for solid model rockets, but not very well for bottle rockets or full scale rockets because of the large decrease in the mass of these rockets during flight as the propellants are expelled.

14. Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Newton’s 3rd Law
For every action there is an equal and opposite reaction.
Thrust is the force which moves the rocket through the air and through space. Thrust is generated by the propulsion system of the rocket through the application of Newton's third law of motion; For every action there is an equal and opposite re-action. In the propulsion system, an engine does work on a gas or liquid, called a working fluid, and accelerates the working fluid through the propulsion system. The re-action to the acceleration of the working fluid produces the thrust force on the engine. The working fluid is expelled from the engine in one direction and the thrust force is applied to the engine in the opposite direction.

15. Traveling to Space
PLTW Gateway
Unit 5 – Lesson 5.3 – Traveling and Living in Space
Image Resources
Microsoft, Inc. (2008). Clip art. Retrieved September 10, 2008, from
National Aeronautics and Space Administration (NASA). (2007). Index of rocket slides. Retrieved July 20, 2009, from