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Bulding a Permanent Human Presence in Space Grades 5-8 Lesson 3: Payload Rocket

The United States and its partners around the world are building the International Space Station (ISS), arguably the most sophisticated engineering project ever undertaken. The ISS is an orbiting laboratory where astronauts conduct research in a variety of disciplines including materials science, physiology in microgravity environments, and Earth remote sensing. The ISS provides a permanent human presence in low Earth orbit. This lesson is one of many grade K-12 lessons developed by Challenger Center to bring the ISS experience to classrooms across the nation. It is part of Building a Permanent Human Presence in Space, one of several Education Modules developed for Challenger Center's Journey through the Universe program. This Education Module addresses the essential question "How can we build a permanent human presence in space?" Start the Journey at www. challenger.org/journey.

Challenger Center, Challenger Center for Space Science Education, and the Challenger Center logotype are registered trademarks of Challenger Center for Space Science Education. No portion of this module may be reproduced without written permission, except for use within a Journey community. ©2004, Challenger Center for Space Science Education. December 2004

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Lesson 3: Payload Rocket

Lesson at a Glance

Lesson Overview

The mass of a rocket can make the difference between a successful flight and a rocket that just sits on the launch pad. In this lesson, students use Newton's Laws of Motion to investigate how a rocket's payload affects the rocket's ability to launch, by constructing a balloon rocket and using it to carry a paper clip payload.

Lesson Duration

Two 45-minute class periods

Core Education Standards

National Science Education Standards Standard B2: Motions and Forces If more than one force acts on an object along a straight line, then the forces will reinforce or cancel one another, depending on their direction and magnitude. Unbalanced forces will cause changes in the speed or direction of an object's motion. Standard B3: Transfer of Energy Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways.

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Related Education Standards

National Science Education Standards Standard E1: Abilities of Technological Design Implement a proposed design: Students should organize materials and other resources, plan their work, make good use of group collaboration where appropriate, choose suitable tools and techniques, and work with appropriate measurement methods to ensure adequate accuracy. Standard E2: Understandings about Science and Technology Technological designs have constraints. Some constraints are unavoidable, for example, properties of materials, or effects of weather and friction; other constraints limit choices in the design, for example, environmental protection, human safety, and aesthetics.

Essential Question

How is the mass of a rocket related to the maximum height it can reach?

Concepts

Students will learn the following concepts: For every action there is an equal and opposite reaction. The mass of a rocket's payload affects its ability to launch. Engineering can help solve real-world problems.

Objectives

Students will be able to do the following: Review the basic principles of rocket propulsion. Determine how a rocket's payload affects its ability to launch.

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Science Overview

"Rocket Science" is often used to describe something complicated. Rocketry can be complicated, of course, but the basic principles are not very difficult. Anyone who has learned to play a sport, who has ridden on a boat, who has played on a rolling chair, or any of hundreds of other perfectly normal activities, has had to develop an instinctive mastery of Newton's Laws of Motion. Converting what the body knows how to do into something that the conscious mind understands, however, is not always so easy. In this lesson, students will have the opportunity to play with the principles of rocket design--acceleration is proportional to the force and inversely proportional to the mass; for every action, there is an equal and opposite reaction--not by memorizing equations and crunching numbers, but by directly experimenting and observing the results of their actions.

What pushes a rocket?

In a famously foolish editorial of 1920, the New York Times chided Dr. Robert H. Goddard, the pioneer of modern rocketry, for not thinking that a rocket needs to push against air in order to work. The Times had the good graces (and surprising sense of humor) to formally retract the editorial in 1969 before Apollo 11 landed on the Moon, dryly noting that the theories of Sir Isaac Newton in fact had been demonstrated to be correct by that time. The principle that propels a rocket is easy to demonstrate in more familiar circumstances. Imagine two persons of identical weight in identical canoes placed end-to-end on a placid lake. If the canoeists sit in the ends of their canoes and push against each other, the two canoes will travel apart, both of them moving across the water. No one had to push against the water or the air in order to make them go, they only had to push each other. If only one canoeist pushes against the other, both canoes will move, although more slowly than when both canoeists pushed. This is an illustration of Newton's Third Law of Motion: for every action (push) there is an equal and opposite reaction--the canoeist who pushes is set in motion, just as the canoeist who is pushed is set in motion. When one canoeist pushes against the other, he moves just as if the other canoeist had pushed against him. What if the canoes are not identical? Imagine that one of the canoes is empty except for the canoeist, while the other has been loaded down with cargo. Now when one canoeist pushes against the other, both will move, but the canoe with cargo will not accelerate as rapidly as the

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unladen canoe. With the same force applied, the canoe that carries the heavier mass is accelerated less and reaches a lower final speed when the pushing is finished. The canoe of lower mass reaches a higher final speed than compared to pushing two unladen canoes apart. What if there is a very big difference between the mass of the canoe and the canoeist compared to whatever the canoeist is pushing against? Imagine just one canoe, loaded with a canoeist and a supply of baseballs. When the canoeist throws a baseball from the canoe, the canoe will move in the opposite direction. The only force applied to the loaded canoe comes from the canoeist's hand pushing the baseball away. The action of the canoeist's hand pushing the baseball is opposed by the reaction of the baseball resisting the push. Since the canoeist is planted in the canoe, the canoeist, the canoe, and the remaining baseballs are pushed away from the thrown ball. Because the canoe with its load of the canoeist and the remaining baseballs weighs much more than an individual baseball, however, the canoe moves much more slowly than the thrown baseball. The canoeist must throw many baseballs in order to get moving. The air around the baseball and the canoeist is not necessary to move the canoe. A ball the same size, but weighing twice as much, thrown at the same speed, would do a better job of propelling the canoe even though it pushes against the same amount of air. It is the act of pushing against the baseball itself that pushes the canoe. There is a limit to how much thrust a human arm can produce--how much force can be applied to the ball. To propel the canoe more effectively by throwing baseballs, the canoeist needs more thrust. A pitching machine that can fling a baseball faster than a human arm would meet the need. However, the weight of the machine is added to the weight of the canoe, partly countering the effectiveness of the machine. A rocket motor works by the same principle as the canoeist throwing baseballs. A rocket motor throws molecules of gas at very high speed, propelling the rocket in the opposite direction. The fuel in a rocket motor is burned in a controlled explosion. If the explosion happened in open space, around the outside of the rocket motor, the hot gases from the explosion would spread in every direction and the rocket motor would go nowhere. Instead, a rocket motor burns its fuel inside a container. If the container had no opening, the burning fuel would push equally hard in all directions against the interior walls of the container (the combustion chamber) and the rocket would go nowhere--at least until the combustion chamber exploded from the pressure. In a real rocket, there is an opening in the wall of the combustion chamber.

Payload Rocket

Lesson at a Glance

Science Overview

Conducting the Lesson

Resources

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The burning rocket fuel pushes equally hard against all surfaces of the combustion chamber, except that the opening is a hole in the wall and so the combustion chamber cannot push back at that spot. The hot gases can escape through the opening. Opposite from the opening, the wall of the combustion chamber resists the pressure of the burning fuel just as before. That resistance--that reaction by the wall against the action of the pressurized gases from the burning fuel--pushes the rocket motor and the rest of the rocket to which it is connected, because there is no opposing force from the part of the combustion chamber where the opening lies. Just like the canoeist throwing baseballs with a machine, the rocket motor itself contributes to the mass of the vehicle to which it is attached. This is the central problem in rocket design: to propel a vehicle with twice the acceleration, or to move twice the cargo with the same acceleration, it is not enough just to build a rocket motor with twice the thrust. The motor itself has mass, and a more-powerful motor will need more fuel and will have to move its own mass as well as the mass of the extra fuel. To achieve twice the acceleration, therefore, requires a motor with much more than twice the thrust.

How high can a rocket carry its payload?

What is a payload? It is the purpose behind launching a space vehicle--it is the "load" that "pays" for the mission to do science or launch communications satellites, etc. A payload destined for space must be accelerated from the speed that the Earth's surface is rotating, 0.46 km/s = 1,040 mph at the equator, to the velocity of low-Earth orbit (LEO) at about 7.8 km/s = 17,400 mph. Not only does the payload need to be accelerated, it also must be lifted from the surface to an altitude of around 300­600 km, which requires a lot of energy. Designing a rocket motor with the thrust needed for a payload of 1000 kg mass (weight of about 2200 lbs.) to accelerate by the necessary amount and to accomplish the change in energy required to lift the payload from the Earth's surface to Low Earth Orbit, is not particularly difficult. However, this barely begins to scratch the surface of the engineering challenges in designing a working space mission. The challenge in building and operating a vehicle (a rocket) to launch a payload into space is that the launch vehicle itself needs to go along for the ride. There is a lot more to move than just the payload. In a space launch vehicle, the payload--the mission's purpose--typically rides in a relatively small container at the top; in the case of the Space Shuttle, the payload rides in the cargo bay in the middle of the shuttle. To move the payload into space, the launch vehicle has enormous (and heavy)

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rocket engines at the rear. It may have strap-on solid- or liquid-fueled boosters attached to the sides. It needs enormous fuel tanks to supply liquid-fueled rockets with the fuel they need to burn to accelerate the payload to the orbital velocity it needs to achieve. Holding all these bits of hardware together is the framework that keeps the rocket engines behind the payload, the massive fuel pumps that transfer gigantic quantities of fuel to be gulped by the rocket engines, the bearings that hold the motors, and the steering systems that pivot the motors in order to keep the flight on course. Covering all this is the skin that protects the vehicle's components from the supersonic winds that threaten to tear it apart on its way up through the atmosphere at several times the speed of sound. Various bits of electronics are needed throughout the vehicle to monitor its systems and to control everything. In the case of the Space Shuttle, there also are the wings and the life support and the orbital steering mechanisms that are not used to launch the vehicle, but that allow astronauts to work in space and then to return to Earth to fly another mission. The payload is only a small fraction of the total mass of material that needs to be launched from the Earth's surface. Most of the energy used up by launching a space vehicle is used in launching the vehicle itself. The payload is only a minor addition to the total mass of the vehicle at launch. By the time the vehicle is in space, however, things are a bit different. By then, most of the fuel is expended--there is little left to burn, but there also is little left to be moved by the motors. In multi-stage rockets, the heavy and powerful lower stages are released after burning all their fuel, greatly decreasing the remaining mass of the launch vehicle. In the case of the Space Shuttle, the solid boosters burn out first and are released, later followed by the large external fuel tank when it is emptied. By the time orbit is achieved, the original launch vehicle is reduced to the payload and enough rocket motors and fuel to move it the last little bit required to reach its final orbit. Traveling on from Earth orbit into deep space requires more energy, of course, but most of the work is accomplished just in lifting the payload to orbit. Large deep space exploration missions like the Magellan mission to Venus and the Galileo mission to Jupiter were carried up to orbit in the cargo bay of the Space Shuttle. The motors for the final push to leave the Shuttle's cargo bay and to go from Earth orbit out into interplanetary space were small enough to fit entirely within the cargo bay along with the spacecraft. Because the payload is a small part of the total vehicle mass, doubling the mass of payload creates only a small decrease in the altitude to which the vehicle can fly. Similarly, halving the payload mass makes

Payload Rocket

Lesson at a Glance

Science Overview

Conducting the Lesson

Resources

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only a small increase in the altitude. Increasing the amount of payload in a mission will have an effect eventually, of course. As the payload mass is increased to become a significant fraction of the mass of the entire launch vehicle, the effect of increasing the payload becomes more and more important in determining the final height of the launch vehicle. When the payload reaches the same mass as the unloaded rocket itself, the height to which the loaded rocket will fly is exactly half the height to which the unloaded rocket could fly. To estimate the height to which a rocket can fly, the total weight of the loaded rocket (payload + rocket) needs to be compared to the total weight of the rocket when its altitude was measured, whether the new total mass is less (so the rocket can fly higher) or more (so the rocket will fly lower).

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Notes:

Payload Rocket

Lesson at a Glance

Science Overview

Conducting the Lesson

Resources

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Conducting the Lesson

Warm-Up & Pre-Assessment

Teacher Materials

Rocket launch picture located in the back of the lesson

Preparation & Procedures

1. Introduce students to Newton's Third Law of Motion that states that for every action, there is an equal and opposite reaction. Show students the picture of the Space Shuttle Endeavour taking off that is located in the back of the lesson. Ask students to describe what is happening. Ask students to identify the action force (the initial force) and the reaction force (what happens due to the action force). (Desired answer: the action force is exerted by the rocket motor propelling hot gases away from the Shuttle; the reaction force is exerted by the pressure of the rocket exhaust pushing against the Shuttle. Some students may give a more detailed answer and note that the exhaust gases apply pressure to the rocket's combustion chamber and push the rocket forward (the action force); the reaction force is produced by the combustion chamber wall resisting the pressure of the hot exhaust gas molecules, deflecting them out the open end of the combustion chamber. "Action" and "reaction" simply indicates that for each identified force, there is an opposing force.) Ask students how they think the mass of a rocket affects how much propulsion it needs. (Desired answer: the heavier the rocket, the more propulsion it will need to get off the ground) What might add mass to a rocket? (Desired answer: e.g., extra fuel, people, scientific instruments) Ask students how engineers compensate for this added weight. (Desired answer: through rocket design, engineering, and making bigger rockets) If we wanted to determine how mass affected a rocket, what could we do? (Desired answer: experiment) Tell students that you just happen to have an experiment written up for them to do just that--experiment with different rocket masses.

2.

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Notes:

Payload Rocket

Lesson at a Glance

Science Overview

Conducting the Lesson

Warm Up & Pre-Assessment Activity: How Does a Payload Affect a Rocket? Lesson Wrap-Up

Resources

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Activity: How Does a Payload Affect a Rocket?

In this activity, students will investigate rocket design by constructing a rocket out of a balloon and using it to carry a paper clip payload.

Teacher Materials

Blackboard or Whiteboard

Student Materials (per group)

Student Worksheet 1 Large long balloons (several per group) Lightweight monofilament fishing line (approximately 50 cm) 1 clothes pin or small binder clip Tape A supply of small paper clips An assortment of straws Marker

Preparation & Procedures

1. 2. Place students into cooperative groups of three or four. Attach one fishing line per group to the ceiling or as high on the wall as possible. Try attaching a paper clip to a fishing line and hooking it on to the light or ceiling tile braces. Allow the remaining line to hang down to the floor or a countertop, and cut any excess. Have students mark off the fishing line in meter intervals with a marker to help them determine the height their rocket traveled. Before students construct their rockets, review the basic principle of rocket propulsion. You may use the following strategies with your students. On the blackboard, draw a cross-section of a balloon with the end tied shut. Ask students to indicate the direction the air is pushing on the inside of the balloon. Ask students in what direction this balloon will move. (Desired answer: None, all of the forces are balanced)

3.

4.

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Draw a cross-section of a balloon with the end not tied shut. Ask students to indicate the direction that the air is moving. (Desired answer: the air is moving out of the neck of the balloon) Ask students in what direction this balloon will move. (Desired answer: in the opposite direction as the air leaving the balloon) Ask students if this is an example of Newton's Third Law of Motion. (Desired answer: Yes, Newton's Third Law states that for every action there is an equal and opposite reaction) Ask students to identify the forces on the balloon and air. (Desired answer: the action force is exerted by the inside wall of the balloon pressing on the air inside the balloon, and the reaction force is the one exerted by the air inside of the balloon on the side of the balloon opposite to its neck. Students may identify the exact opposite situation, which is equally valid.)

Payload Rocket

Lesson at a Glance

Science Overview

4. Tell students they will be using balloons and the principles that they just observed to determine how the mass of various paperclip payloads affects a balloon rocket's ability to launch from the floor to the ceiling. The paper clip payload is a model of the scientific instruments that a real rocket would carry. Instruct students to follow the directions in Student Worksheet 1.

Conducting the Lesson

Warm Up & Pre-Assessment Activity: How Does a Payload Affect a Rocket? Lesson Wrap-Up

Reflection & Discussion

Have students share the data. Ask students, based on their observations, to describe how the mass of the payload affected the rocket's ability to launch from the floor to the ceiling. Ask students if anything surprised them about their data.

Resources

Transfer of Knowledge

In order for students to apply what they have learned, challenge them to a rocket race. Have them use their data to choose the optimal payload size. Test their decision by seeing whose rocket travels the highest. Ask students to write their payload size and an explanation of their choice on a piece of paper and turn it in for assessment.

Extensions

Have students complete the same experiment again, except have the rocket travel horizontally (sideways) instead of vertically. The rocket should be able to move weight that it could not lift. Have students research why. Encourage students to pursue flying model rocketry outside of class using model kits. Encourage them to use geometry to measure the altitude of the rockets.

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Assessment Criteria for Activity

4 Points Student accurately constructed and tested their balloon rocket. Student thoroughly recorded all observations in Data Table 1. Student accurately answered all questions and displayed thorough understanding of all 3 Points Student accurately constructed and tested their balloon rocket. Student recorded most of their observations in Data Table 1. Student accurately answered all questions and displayed thorough understanding of the major concepts. 2 Points Student constructed and tested their balloon rocket. Student recorded some observations in Data Table 1. Student answered some questions and displayed an understanding of the major concepts. 1 Point Student constructed and tested their balloon rocket. Student recorded a few observations in Data Table 1. Student answered a few questions and displayed a limited understanding of major concepts. 0 Points Student did not turn in any work.

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Notes on Activity:

Payload Rocket

Lesson at a Glance

Science Overview

Conducting the Lesson

Warm Up & Pre-Assessment Activity: How Does a Payload Affect a Rocket? Lesson Wrap-Up

Resources

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Lesson Wrap-Up

Lesson Closure

Discuss with students how the testing they conducted compares to the testing done by scientists and engineers. What are some of the things scientists have to consider when planning a mission to space?

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Notes:

Payload Rocket

Lesson at a Glance

Science Overview

Conducting the Lesson

Warm Up & Pre-Assessment Activity: How Does a Payload Affect a Rocket? Lesson Wrap-Up

Resources

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Resources

Internet Resources & References

Student-Friendly Web Sites: NASA's Beginner's Guide to Model Rockets http://www.lerc.nasa.gov/WWW/K-12/airplane/bgmr.html PBS Kids - Model Rockets http://pbskids.org/dragonflytv/show/modelrockets.html Rockets Away http://cse.ssl.berkeley.edu/AtHomeAstronomy/activity_06.html Teacher-Oriented Web Sites: 3-2-1 Liftoff http://spacelink.nasa.gov/products/3-2-1.Liftoff/ Challenger Center http://www.challenger.org/journey/ Pencil Rockets http://www.grc.nasa.gov/WWW/K-12/TRC/Rockets/pencil_ rocket.html National Association of Rocketry http://www.nar.org/ Journey through the Universe http://www.challenger.org/journey

Acknowledgments

Adapted from Rockets: An Educator's Guide with Activities in Science, Mathematics, and Technology, NASA EG-2003-01-108-HQ.

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Teacher Answer Key

1. 2. 3. Answers will vary. Answers will vary. You could make a bigger rocket by blowing up your balloon bigger or adding a second balloon. Lesson at a Glance Payload Rocket

4. Reaction Force Science Overview

Action Force

Conducting the Lesson

Resources

Internet Resources & References Teacher Answer Keys

Student Worksheet 1 Rocket Team _____________________________________________ Date ___________ Materials:

Large long balloon Fishing line (approximately 50 cm) 1 clothes pin or small binder clip 20 small paper clips Tape Straw Marker

Procedures:

1. Blow up a balloon. Measure the circumference of the balloon (distance around) with a piece of string and use the marker to mark the circumference on the string. Each time you blow up the balloon, use your string to make sure it always has the same circumference for consistency. Hold it shut with a clothes pin or clip. You will remove the clothespin before launch. Tape a paper clip to the side of the balloon. The paper clip payload is a model for the scientific instruments that a real rocket would carry. Attach a straw to the side of your rocket (balloon) using tape. Be sure that the straw runs lengthwise along the balloon. This will be your guide and attachment to your fishing line. Thread the fishing line through the straw and attach one end of the fishing line to the ceiling or a high place. You will launch the rocket by removing the clothes pin. NOTE: The fishing line should be taut for the rocket to travel successfully up the line, and the clipped balloon nozzle must be untwisted before release.

2.

3.

4.

www.challenger.org/journey

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5.

Predict how many paper clips you think your rocket can lift to the ceiling. (2 small paper clips = approximately 1 gram) Record your prediction in the space below.

6.

Test your rocket. First tape no paper clips onto the balloon. Launch your rocket by releasing the clothes pin. Observe how high your rocket climbed up the fishing line and record your observations in Data Table 1. Continue launching your rocket, but increase the number of paper clips each time. Record your data in Data Table 1. Graph the results of your experiment and answer the questions on the next page.

7.

Data Table 1 Number of Paper Clips

0 1 2 3 4 5 6 7 8 9 10

Height Reached

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Questions

1. What was the highest altitude your rocket reached?

2.

What number of paper clips allowed your rocket to travel the highest? Were you surprised by your observations? Explain your findings.

3.

What other ways could you increase the lifting capacity of your rocket?

4.

Newton's third law of motion states that for every action there is an equal and opposite reaction. Draw a sketch of your rocket and indicate with arrows and labels the action force and the reaction force.

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