Earth-to-Orbit Design Challenge
March 25, 2002
Re-printed with permission from the November/December 2001 issue of Connect MagazineDesign challenges are exciting and rich opportunities to engage middle school students in the problem-solving processes that engineers and scientists use every day. While building scientific habits of mind, design challenges also broaden horizons by simulating experiences that students will likely face in an increasingly technical workplace.
The Thermal Protection Systems (TPS) Challenge, part of the NASA Earth-to-Orbit curriculum, presents students with a real-life problem faced by NASA engineers: construct a heat shield that will protect a spacecraft from 3000° F re-entry temperatures as it returns to Earth. In the TPS challenge, students must design a heat shield model that can also withstand extreme temperature conditions. My middle school students get hooked immediately. As they build several successive models, students become immersed in a rewarding process of improvement that is fueled by their original thoughts and critical reflection.
Designing the model
The heat shield models are built of dowels, machine screws, low-temperature hot- melt glue, hex nuts, washers, copper screen, and foil. These supplies are readily available at most local hardware stores. The dowel-and-screw model is meant to represent the nosecone of a spacecraft. The dowel and the glue are the spacecraft’s inner cabin. The screw represents the skin of the spacecraft; students must attach their heat shield to this "skin." To simulate the effects of re-entry, we position the model a short distance from a small, propane torch (to be used only by the teacher). The goal is for students to design a shield that protects the glue from the heat of the torch. Safety considerations are clearly addressed in the curriculum guide; read the guide carefully before proceeding with this project.Students gasp when I present them with the minimal supplies they are allowed to use for the first round of designs. To begin, I give students the dowel and screw (glued together), 2 hex nuts, 2 washers, and a 3" square piece of copper screening. At first, it is hard to imagine how a tiny piece of screen filled with holes could protect the glue at all. Students know their success will be judged by how long the screw stays on—in other words, how long the glue lasts.
Intense discussions between student partners begin immediately:
"We can make a coat around the screw and that will stop the heat."
"LetÂ’s make a wall to push the heat back."
"We should put the shield at the top of the screw, not at the bottom . . ."
Typically, their first-round designs are relatively simple. Many students look at the problem based on their own lives, without considering the properties of the materials they have to use. For example, several students usually wrap the copper screen around the screw thinking that it will act like a firefighterÂ’s jacket. Others attach the square screen directly to the end of the screw thinking that it will act as a deflecting shield. In general, students use the screen just as it has been given to them; they do not immediately consider all the ways in which it could be altered, connected, or manipulated.
Before testing
Students fill out a "spec sheet." They have to include a detailed drawing of their model and an explanation of how it is supposed to work. As each model is brought up to the testing area, teams of students present their ideas. Getting students to articulate their ideas usually proves to be challenging. As the presentations proceed, we generate a list of words to explain how the shield works, such as block, bounce, and soak up. These are not scientific phrases that I provide; instead they are words that come out of studentsÂ’ own working theories. Later, I introduce them to more sophisticated terminology to describe the same ideas they are talking about.
I urge students to be precise in their explanations. When I first ask them to describe how their model will work, they often provide a vague explanation, "ItÂ’s just going to stop the heat." They soon realize that, instead of using the word "it", they have to refer to specific elements of their designs. If students need prompting, I ask them, "WhatÂ’s going to happen when heat comes into contact with this part here?" In this way, they begin to see that a TPS model can have several different parts, each designed to protect the glue. Students also begin to see the need for naming different design elements, and we start to classify designs into types. When they say, "HereÂ’s another jacket-type model," it gives me a chance to ask, "How is it different from the one we tested earlier?" Soon, they are posing and answering these systematic analysis questions before I can even ask them.
Testing
Students usually gather around the testing set-up with intense anticipation – eager to see whether their theories hold true. During testing, I stress that designs which fail are part of the normal design process. We emphasize improvement over competition; I tell students that they are competing against themselves, always trying to better their time from the previous model. To that end, we focus on how the shield actually works and how it could be improved. My role is to ask guiding questions, such as:
"How did the heat get from the flame to the glue? Describe the pathway."
"Where was the model glowing during testing? What could that mean?"
"What design elements could you change to better protect the glue?"
The first round of testing typically ends quickly; most models last 20 seconds or less until the glue melts and the screw drops off. Students quickly realize that the material — the metal screw and screen — do not behave as they expected. They demand to know more about how heat travels through metals. At this point, we usually take a two-day detour from the NASA curriculum to learn more about conduction. To do this, we use instruments called conductometers, which include five spokes, each one made of a different metal. The end of each spoke has a tiny well that students fill with candle wax. These spokes are attached to a central hub, which is heated over a burner. By measuring the time it takes for the wax to melt from each spoke, students can compare the different rates of heat transfer along different metals. After we collect our data, I encourage students to conjecture how the TPS trials would go differently if we used screens and screws made out of different metals. We return to the NASA challenge with a new understanding of heat transfer, and new ideas about how to limit pathways of conduction to the glue in our models.
Redesign
Students begin work on their second model using the same materials as their first. By this time, they are intensely engaged in construction and excitedly exchange and debate ideas about how to build a "top performer." Many students now realize that they can pull out individual threads from the copper screen and use them to connect the screen to the screw and thereby restrict conduction to the glue. They also realize that they can cut, fold, bend, and twist the screen into any shape they want. The second round models are typically much more complex. Once their latest models are complete, students again fill out spec sheets. Students compare their first and second round spec sheets and we discuss how they have improved in their thinking, writing, and drawing.
During the second round of testing, many students improve their first round time by two minutes or more. Each student takes great pride in beating his or her own first round time; we celebrate and display our results using graphs and percentage improvement calculations. On their spec sheets, students write conclusions that analyze which parts worked well and why, and which parts still need improvement.
A continuing process
The NASA curriculum suggests several places to go from here. My students frequently go on to a third model, this time using copper screen and a 3" square of aluminum foil. Teachers can challenge students to build the longest-lasting model for the cheapest price and contact local engineers to come and speak with students about their work. In the past, we have sent materials to make a heat shield model to area engineers, and they have sent them back to us for testing. My students are always extremely excited to see how the engineersÂ’ designs will stand up to theirs!
Through the iterative process of design-test-redesign in this unit, students get a real flavor for the analytic process that engineers and all scientists must go through in their daily work. I use the unit to kick off the school year because it builds habits that underlie effective problem-solving in science. Additionally, students develop data analysis and presentation skills, lab report skills, and measurement skills in a context which is exciting and meaningful to them.
Because the TPS curriculum presents a real problem that professional scientists and engineers face, students get authentic exposure to the demands and excitement of the technical workplace, and experience the joy inherent in learning, conceptualizing, and applying ideas. Students actually ask me throughout the unit, "Would it be possible for me to do something like this for a job when I grow up?" In a very real way, the TPS curriculum broadens horizons; students revel in the power of their own creative thinking, and all that they can accomplish with it.
The NASA Earth to Orbit Design Challenges curriculum was sponsored by NASA and designed by TERC.
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