Aerospace Engineering

Grade Level: 
High School
Subject: 
STEM, Pre-Engineering, Aerospace
Lesson Focus
Lesson focuses on aerospace engineering and how space flight has been achieved from an engineering vantage point. Students build and launch a model rocket and consider the forces on a rocket, Newton's Laws, and other principles and challenges of actual space vehicle launch. They design their structure on paper, learn about aerospace engineering, launch their rocket, and share observations with their class.
 
Lesson Synopsis 
The "Blast Off" lesson explores rocketry, and the principals of space flight. Students work in teams with teacher supervision and construct and launch a rocket from an inexpensive kit. They observe their own achievements and challenges, as well as those of other student teams, complete a reflection sheet, and present their experiences to the class.  
 
 
Time Needed
Two to four 45-minute sessions.
 
Objectives 
 
ª  Learn about aerospace engineering.
ª  Learn about engineering design and redesign.
ª  Learn about space flight.
ª  Learn how engineering can help solve society's challenges.
ª  Learn about teamwork and problem solving.
 
Anticipated Learner Outcomes
As a result of this activity, students should develop an understanding of: 
 
ª  aerospace engineering
ª  engineering design
ª  space flight
ª  teamwork
 
Lesson Activities 
Students explore how engineers have developed rocketships over the years, and learn about the principals of rocketry. They work in teams to construct and launch a model rocket from a kit under teacher supervision. The students compare their accomplishments and challenges with those of other student teams, complete a reflection sheet, and present to the class.
 
 
 Resources/Materials
 
ª  Teacher Resource Documents
ª  Student Resource Sheet  
ª  Student Worksheet
 
Suggested resources for model rocket kits:
oLocal or national rocket competitions
 Internet access (optional) to explore http://www.grc.nasa.gov/WWW/K-12/rocket/for research and to use online rocket simulator 
 
 
Internet Connections
 
ª  TryEngineering (http://www.tryengineering.org)
ª  Timeline of Rocket History (http://history.msfc.nasa.gov/rocketry/)
ª  NASA Beginners Guide to Rockets (http://www.grc.nasa.gov/WWW/K-12/rocket/bgmr.html)
ª  European Space Agency - Space Engineering (http://www.esa.int/SPECIALS/Space_Engineering)
ª  Rocketry Planet (http://www.rocketryplanet.com)
ª  National Science Education Standards (http://www.nsta.org/publications/nses.aspx)
ª  ITEA Standards for Technological Literacy (http://www.iteaconnect.org/TAA)
 
 Recommended Reading
 
ª  Rockets and Missiles: The Life Story of a Technology (ISBN: 978-0801887925)
ª  Rocket and Spacecraft Propulsion: Principles, Practice and New Developments (ISBN: 978-3642088698)
ª  It's ONLY Rocket Science (ISBN: 978-0387753775)
ª  "A Pictorial History of Rockets"
 
Optional Writing Activity 
 
ª  Write an essay or a paragraph describing an example of rockets might be used to help society in peaceful times. 
 
Extension Activity 
 
ª  Have older or more advanced students use an altimeter to measure acceleration as part of this lesson and incorporate g-force discussions. 
 
Safety Notes 
 
ª  Be sure to follow rocket manufacturer's guidelines and your school's safety policies.
ª  Teachers who have never supervised a rocket launch may want to team with a teacher who has for their first launch.
ª  An alternate to rocket launch kits would be to use a foot pump and launch an air rocket (using an empty soda bottle or other container for the rocket). 
 
Lesson Goal 
The "Blast Off!" lesson focuses on aerospace engineering and how space flight has been achieved from an engineering vantage point. Students build and launch a model rocket and consider the forces on a rocket, Newton's Laws, and other principles and challenges of actual space vehicle launch. They design their structure on paper, learn about aerospace engineering, launch their rocket, and share observations with their class.  
 
 
Procedure
1.Show students the student reference sheets. These may be read in class or provided as reading material for the prior night's homework. 
2.To introduce the lesson, consider asking the students how they think a rocket can fly and how engineers have to consider payload, weather, and the shape and weight of a rocket when developing a new or re-engineered rocket design.  
3.Teams of 3-4 students will consider their challenge, read about rocketry, and explore the online rocket simulator (if internet access is available)
4.Teams next build and launch their rocket as a team, and observe the flight patterns of other rockets that are launched.
5.Teams reflect on the experience, and present to the class.
 
Rocket Principles
 
A rocket in its simplest form is a chamber enclosing a gas under pressure. A small opening at one end of the chamber allows the gas to escape, and in doing so provides a thrust that propels the rocket in the opposite direction. A good example of this is a balloon. Air inside a balloon is compressed by the balloon's rubber walls. The air pushes back so that the inward and outward pressing forces are balanced. When the nozzle is released, air escapes through it and the balloon is propelled in the opposite direction. 
 
When we think of rockets, we rarely think of balloons. Instead, our attention is drawn to the giant vehicles that carry satellites into orbit and spacecraft to the Moon and planets. Nevertheless, there is a strong similarity between the two. The only significant difference is the way the pressurized gas is produced. With space rockets, the gas is produced by burning propellants that can be solid or liquid in form or a combination of the two. 
 
One of the interesting facts about the historical development of rockets is that while rockets and rocket-powered devices have been in use for more than two thousand years, it has been only in the last three hundred years that rocket experimenters have had a scientific basis for understanding how they work. 
 
The science of rocketry began with the publishing of a book in 1687 by the English scientist Sir Isaac Newton. His book, entitled Philosophiae Naturalis Principia Mathematica, described physical principles in nature. Today, Newton's work is usually just called the Principia. In the Principia, Newton stated three important scientific principles that govern the motion of all objects, whether on Earth or in space. Knowing these principles, now called Newton's Laws of Motion, rocketeers have been able to construct the modern giant rockets of the 20th century such as the Saturn V and the Space Shuttle. 
 
Newton's Laws of Motion 
 
·Objects at rest will stay at rest and objects in motion will stay in motion in a straight line unless acted upon by an unbalanced force. 
·Force is equal to mass times acceleration. 
·For every action there is always an opposite and equal reaction. 
 
All three laws are really simple statements of how things move. But with them, precise determinations of rocket performance can be made. 
 
Newton's First Law
This law of motion is just an obvious statement of fact, but to know what it means, it is necessary to understand the terms rest, motion, and unbalanced force. 
 
Rest and motion can be thought of as being opposite to each other. Rest is the state of an object when it is not changing position in relation to its surroundings. If you are sitting still in a chair, you can be said to be at rest. This term, however, is relative. Your chair may actually be one of many seats on a speeding airplane. The important thing to remember here is that you are not moving in relation to your immediate surroundings. If rest were defined as a total absence of motion, it would not exist in nature. Even if you were sitting in your chair at home, you would still be moving, because your chair is actually sitting on the surface of a spinning planet that is orbiting a star. The star is moving through a rotating galaxy that is, itself, moving through the universe. While sitting "still," you are, in fact, traveling at a speed of hundreds of kilometers per second. 
 
Motion is also a relative term. All matter in the universe is moving all the time, but in the first law, motion here means changing position in relation to surroundings. A ball is at rest if it is sitting on the ground. The ball is in motion if it is rolling. A rolling ball changes its position in relation to its surroundings. When you are sitting on a chair in an airplane, you are at rest, but if you get up and walk down the aisle, you are in motion. A rocket blasting off the launch pad changes from a state of rest to a state of
motion. 
 
The third term important to understanding this law is unbalanced force. If you hold a ball in your hand and keep it still, the ball is at rest. All the time the ball is held there though, it is being acted upon by forces. The force of
gravity is trying to pull the ball downward, while at the same time your hand is pushing against the ball to hold it up. The forces acting on the ball are balanced. Let the ball go, or move your hand upward, and the forces become unbalanced. The ball then changes from a state of rest to a state of motion. 
 
In rocket flight, forces become balanced and unbalanced all the time. A rocket on the launch pad is balanced. The surface of the pad pushes the rocket up while gravity tries to pull it down. As the engines are ignited, the thrust from the rocket unbalances the forces, and the rocket travels upward. Later, when the rocket runs out of fuel, it slows down, stops at the highest point of its flight, then falls back to Earth.
 
(Source: NASA - Visit http://www.grc.nasa.gov/WWW/K-12/rocketfor more details on rocketry.)
 
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. 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 parallel to Earth's surface. If the rocket shoots the spacecraft fast enough, the spacecraft will orbit Earth. As long as another unbalanced force, such as friction with gas molecules in orbit or the firing of a rocket engine in the opposite direction from its movement, does not slow the spacecraft, it will orbit Earth forever.
 
Now that the three major terms of this first law have been explained, it is possible to restate this law. If an object, such as a rocket, is at rest, it takes an unbalanced force to make it move. If the object is already moving, it takes an unbalanced force, to stop it, change its direction from a straight line path, or alter its speed. 
 
Newton's Third Law
For the time being, we will skip the second law and go directly to the third. This law states that every action has an equal and opposite reaction. If you have ever stepped off a small boat that has not been properly tied to a pier, you will know exactly what this law means.
 
A rocket can lift off from a launch pad only when it expels gas out of its engine. The rocket pushes on the gas, and the gas in turn pushes on the rocket. The whole process is very similar to riding a skateboard. Imagine that a skateboard and rider are in a state of rest (not moving). The rider jumps off the skateboard. In the third law, the jumping is called an action. The skateboard responds to that action by traveling some distance in the opposite direction. The skateboard's opposite motion is called a reaction. When the distance traveled by the rider and the skateboard are compared, it would appear that the skateboard has had a much greater reaction than the action of the rider. This is not the case. The reason the skateboard has traveled farther is that it has less mass than the rider. This concept will be better explained in a discussion of the second law. 
 
With rockets, the action is the expelling of gas out of the engine. The reaction is the movement of the rocket in the opposite direction. To enable a rocket to lift off from the launch pad, the action, or thrust, from the engine must be greater than the mass of the rocket. In space, however, even tiny thrusts will cause the rocket to change direction. 
 
One of the most commonly asked questions about rockets is how they can work in space where there is no air for them to push against. The answer to this question comes from the third law. Imagine the skateboard again. On the ground, the only part air plays in the motions of the rider and the skateboard is to slow them down. Moving through the air causes friction, or as scientists call it, drag. The surrounding air impedes the action- reaction. As a result rockets actually work better in space than they do in air. As the exhaust gas leaves the rocket engine it must push away the surrounding air; this uses up some of the energy of the rocket. In space, the exhaust gases can escape freely. 
 
Newton's Second Law
This law of motion is essentially a statement of a mathematical equation. The three parts of the equation are mass (m), acceleration (a), and force (f). Using letters to symbolize each part, the equation can be written as follows: 
f = ma By using simple algebra, we can also write the equation two other ways: 
a = f/m
m = f/a
The first version of the equation is the one most commonly referred to when talking about Newton's second law. It reads: force equals mass times acceleration. To explain this law, we will use an old style cannon as an example. 
 
When the cannon is fired, an explosion propels a cannon ball out the open end of the barrel. It flies a kilometer or two to its target. At the same time the cannon itself is pushed backward a meter or two. This is action and reaction at work (third law). The force acting on the cannon and the ball is the same. What happens to the cannon and the ball is determined by the second law. Look at the two equations below. 
f = m(cannon) * a(cannon)
f = m(ball) * a(ball)
 
The first equation refers to the cannon and the second to the cannon ball. In the first equation, the mass is the cannon itself and the acceleration is the movement of the cannon. In the second equation the mass is the cannon ball and the acceleration is its movement.
 
The first equation refers to the cannon and the second to the cannon ball. In the first equation, the mass is the cannon itself and the acceleration is the movement of the cannon. In the second equation the mass is the cannon ball and the acceleration is its movement. Because the force (exploding gun powder) is the same for the two equations, the equations can be combined and rewritten below: 
 
m(cannon) * a(cannon) = m(ball) * a(ball)
 
In order to keep the two sides of the equations equal, the accelerations vary with mass. In other words, the cannon has a large mass and a small acceleration. The cannon ball has a small mass and a large acceleration. 
 
Let's apply this principle to a rocket. Replace the mass of the cannon ball with the mass of the gases being ejected out of the rocket engine. Replace the mass of the cannon with the mass of the rocket moving in the other direction. Force is the pressure created by the controlled explosion taking place inside the rocket's engines. That pressure accelerates the gas one way and the rocket the other. Some interesting things happen with rockets that don't happen with the cannon and ball in this example. With the cannon and cannon ball, the thrust lasts for just a moment. The thrust for the rocket continues as long as its engines are firing. Furthermore, the mass of the rocket changes during flight. Its mass is the sum of all its parts. Rocket parts include engines, propellant tanks, payload, control system, and propellants. By far, the largest part of the rocket's mass is its propellants. But that amount constantly changes as the engines fire. That means that the rocket's mass gets smaller during flight. In order for the left side of our equation to remain in balance with the right side, acceleration of the rocket has to increase as its mass decreases. That is why a rocket starts off moving slowly and goes faster and faster as it climbs into space. 
 
Newton's second law of motion is especially useful when designing efficient rockets. To enable a rocket to climb into low Earth orbit, it is necessary to achieve a speed, in excess of 28,000 km per hour. A speed of over 40,250 km per hour, called escape velocity, enables a rocket to leave Earth and travel out into deep space. Attaining space flight speeds requires the rocket engine to achieve the greatest action force possible in the shortest time. In other words, the engine must burn a large mass of fuel and push the resulting gas out of the engine as rapidly as possible. Newton's second law of motion can be restated in the following way: the greater the mass of rocket fuel burned, and the faster the gas produced can escape the engine, the greater the thrust of the rocket. 
 
Putting Newton's Laws of Motion Together
An unbalanced force must be exerted for a rocket to lift off from a launch pad or for a craft in space to change speed or direction (first law). The amount of thrust (force) produced by a rocket engine will be determined by the mass of rocket fuel that is burned and how fast the gas escapes the rocket (second law). The reaction, or motion, of the rocket is equal to and in the opposite direction of the action, or thrust, from the engine (third law).
 
How Rockets Fly
 
In flight, a rocket is subjected to four forces; weight, thrust, and the aerodynamic forces, lift and drag. The magnitude of the weight depends on the mass of all of the parts of the rocket. The weight force is always directed towards the center of the earth and acts through the center of gravity, the yellow dot on the figure. The magnitude of the thrust depends on the mass flow rate through the engine and the velocity and pressure at the exit of the nozzle. The thrust force normally acts along the longitudinal axis of the rocket and therefore acts through the center of gravity. Some full scale rockets can move, or gimbal, their nozzles to produce a force which is not aligned with the center of gravity. The resulting torque about the center of gravity can be used to maneuver the rocket. The magnitude of the  aerodynamic forces depends on the shape, size, and velocity of the rocket and on properties of the atmosphere. The aerodynamic forces act through the center of pressure, the black and yellow dot on the figure. Aerodynamic forces are very important for model rockets, but may not be as important for full scale rockets, depending on the mission of the rocket. Full scale boosters usually spend only a short amount of time in the atmosphere. 
 
In flight, the magnitude -- and sometimes the direction -- of the four forces is constantly changing. The response of the rocket depends on the relative magnitude and direction of the forces, much like the motion of the rope in a "tug-of- war" contest. If we add up the forces, being careful to account for the direction, we obtain a net external force on the rocket. The resulting motion of the rocket is described by Newton's laws of motion. 
 
Although the same four forces act on a rocket as on an airplane, there are some important differences in the application of the forces: 
 
·On an airplane, the lift force (the aerodynamic force perpendicular to the flight direction) is used to overcome the weight. On a rocket, thrust is used in opposition to weight. On many rockets, lift is used to stabilize and control the
direction of flight. 
 
·On an airplane, most of the aerodynamic forces are generated by the wings and the tail surfaces. For a rocket, the aerodynamic forces are generated by the fins, nose cone, and body tube. For both airplane and rocket, the aerodynamic forces act through the center of pressure (the yellow dot with the black center on the figure) while the weight acts through the center of gravity (the yellow dot on the figure). 
 
·While most airplanes have a high lift to drag ratio, the drag of a rocket is usually much greater than the lift. 
 
·While the magnitude and direction of the forces remain fairly constant for an airplane, the magnitude and direction of the forces acting on a rocket change dramatically during a typical flight.  
 
Commercial Spaceflight - News
 
SpaceShipTwo: The World’s First Commercial Spaceship 
 
Early on Wednesday 4th May 2011, in the skies above Mojave Air and Spaceport CA, SpaceShipTwo, the world’s first commercial spaceship, demonstrated its unique reentry ‘feather’ configuration for the first time. This test flight, the third in less than two weeks, marks another major milestone on the path to powered test flights and commercial operations. SpaceShipTwo (SS2), named VSS Enterprise, has now flown solo seven times since its public roll-out in December 2009 and since the completion of its ground and captive -carry test program.
 
After a 45 minute climb to the desired altitude of 51,500 feet, SS2 was released cleanly from VMS Eve and established a stable glide profile before deploying, for the first time, its re-entry or “feathered” configuration by rotating the tail section of the vehicle upwards to a 65 degree angle to the fuselage. It remained in this configuration with the vehicle’s body at a level pitch for approximately 1 minute and 15 seconds whilst descending, almost vertically, at around 15,500 feet per minute, slowed by the powerful shuttlecock-like drag created by the raised tail section. At around 33,500 feet the pilots reconfigured the spaceship to its normal glide mode and executed a smooth runway touch down, approximately 11 minutes and 5 seconds after its release from VMS Eve. All objectives for the flight were met and detailed flight data is now being analysed by the engineers at Scaled Composites, designers and builders of Virgin Galactic’s sub-orbital spacecraft.
 
George Whitesides, CEO and President of Virgin Galactic, said: “We have also shown this morning that the unique feathering re-entry mechanism, probably the single most important safety innovation within the whole system, works perfectly. This is yet another important milestone successfully passed for Virgin Galactic, and brings us ever closer to the start of commercial operations.”
 
Perhaps the most innovative safety feature employed by SpaceshipOne and now SpaceShipTwo is the unique way it returns into the dense atmosphere from the vacuum of space. This part of space flight has always been considered as one of the most technically challenging and dangerous. The inspiration for what is known as the feathered re-entry was the humble shuttlecock, which like SpaceShipTwo relies on aerodynamic design and laws of physics to control speed and attitude.
 
Once out of the atmosphere the entire tail structure of the spaceship can be rotated upwards to about 65º. The feathered configuration allows an automatic control of attitude with the fuselage parallel to the horizon. This creates very high drag as the spacecraft descends through the upper regions of the atmosphere. The feather configuration is also highly stable, effectively giving the pilot a hands-free re-entry capability, something that has not been possible on spacecraft before, without resorting to computer controlled fly-by-wire systems. The combination of high drag and low weight (due to the very light materials used to construct the vehicle) mean that the skin temperature during re-entry stays very low compared to previous manned spacecraft and thermal protection systems such as heat shields or tiles are not needed. During a full sub-orbital spaceflight, at around 70,000ft following re-entry, the feather lowers to its original configuration and the spaceship becomes a glider for the flight back to the spaceport runway.
 
(Source: Virgin Galactic. More details at http://www.virgingalactic.com)
 
Student Worksheet:
 
Engineering Teamwork and Planning
You are part of a team of engineers given the challenge of building a model
rocket from a kit that can rise the highest and straightest compared with other student teams in your class. You'll research ideas online (if you have internet access), learn about rocket design and flight, and work as a team to construct and test your rocket. You'll consider the results of other teams, complete a reflection sheet, and share your experiences with the class.
 
Research Phase
Read the materials provided to you by your teacher. If you have access to the internet, also visit http://www.grc.nasa.gov/WWW/K-12/rocket/for additional research and to use the online rocket simulator, RocketModeler III.  
 
Planning and Design Phase
On a separate piece of paper draw a detailed diagram of how your rocket will look when completed and estimate how high you believe your rocket with travel. Is there anything you can do to encourage your rocket to go higher and straighter?
 
Build and Launch
 As a team, build your rocket -- but always under the supervision of your teacher! You'll then test the rocket. Be sure to observe how high and how straight the rockets built by other teams go. 
 
Reflection/Presentation Phase
Complete the attached student reflection sheet and present your experiences with this activity to the class. 
 
 Reflection  
Complete the reflection questions below:
 
1. How did the height you estimated your rocket would reach compare with the actual estimated height?   
 
2. What do you think might have caused any differences in the height you achieved?
 
3. Did your rocket launch straight up? If not, why do you think it veered off course?
 
4. Do you think that this activity was more rewarding to do as a team, or would you have preferred to work alone on it? Why?  
 
5. Did you adjust your model rocket at all? How? Do you think this helped or hindered your results?
 
6. How do you think the rocket would have behaved differently if it were launched in a weightless atmosphere?
  
7. What safety measures do you think engineers consider when launching a real rocket? Consider the location of most launch sites as part of your answer.
 
8. When engineers are designing a rocket which will carry people in addition to cargo, how do you think the rocket will change in terms of structural design, functionality, and features?
 
 9. Do you think rocket designs will change a great deal over the next ten years? How?
 
 10. What tradeoffs do engineers have to make when considering the space/weight of fuel vs. the weight of cargo?
 
 
Alignment to Curriculum Frameworks
 
National Science Education Standards Grades 9-12 (ages 14-18)
CONTENT STANDARD A: Science as Inquiry
ª As a result of activities, all students should develop abilities necessary to do scientific inquiry 
CONTENT STANDARD B: Physical Science 
ª As a result of their activities, all students should develop understanding of
 Chemical reactions 
 Motions and forces 
CONTENT STANDARD E: Science and Technology
ªAs a result of activities, all students should develop
 Abilities of technological design 
Understandings about science and technology 
CONTENT STANDARD F: Science in Personal and Social Perspectives
ªAs a result of activities, all students should develop understanding of
Science and technology in local, national, and global challenges 
CONTENT STANDARD G: History and Nature of Science
ªAs a result of activities, all students should develop understanding of  
 Science as a human endeavor 
 Nature of scientific knowledge 
 Historical perspectives 
 
Standards for Technological Literacy - All Ages
The Nature of Technology
ª  Standard 1: Students will develop an understanding of the characteristics and scope of technology.
Technology and Society
ªStandard 6: Students will develop an understanding of the role of society in the development and use of technology.
ª  Standard 7: Students will develop an understanding of the influence of technology on history.
Design
ª  Standard 8: Students will develop an understanding of the attributes of design.
ª Standard 9: Students will develop an understanding of engineering design.
ªStandard 10: Students will develop an understanding of the role of troubleshooting, research and development, invention and innovation, and experimentation in problem solving.
Abilities for a Technological World
ª  Standard 11: Students will develop abilities to apply the design process.