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					Physical Science

Space Shuttle Safety: Redundant Systems – Teacher Notes Time Requirement: 50-90 minutes This activity uses a problem based learning format to introduce circuitry. The lesson introduces the definition of a circuit as an unbroken conductive path, simple circuit diagrams, current flow, and series and parallel circuits. You can either have small groups work through all of the steps, or use a “jigsaw” format and have different groups working on steps two and three. Then, reform the groups so that each group has at least one member that has built each type of circuit. Depending on the amount of materials that you have, you may need to increase the group size for the final circuit. As an introduction to this activity, you may want to show the electronic video clip titled, “STS_Launch.” Materials (Steps 1-3): • Battery holder and battery • Socket • Light bulb • Wires (at least 10) • Switches (at least 4) Materials (Step 5): • Battery holder and battery • Socket • Light bulb • Wires (at least 20) • Switches (at least 10) Procedure Introduce the lesson by discussing the complexity of NASA’s space shuttles. Describe what redundancy is and why it is important. A good “Earthbound” analogy is that of a car and spare tire. The spare tire is a backup, or redundancy. If you have one spare tire, you have a single fault (you can get one flat) redundancy. Would you drive through a desert with any less than one spare? The shuttle also has many redundant systems so that critical failures will not jeopardize the mission and crew. Step One Students will build a simple circuit consisting of a bulb, battery and switch. They will also sketch the diagram. Have the groups share their diagrams with the class. At this point, do not expect them to draw formal circuit diagrams. This will be introduced in step four. A circuit diagram for step one is located in figure 2. Step Two In this step, students will construct circuits with switches in series. Figures 3 and 4 show the proper circuit diagrams for single and double redundant circuits. Test student circuits

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Physical Science by closing one or two switches and only letting them operate the other switches to turn off the light. Have students share their diagrams. Step Three In this step, students will construct circuits with switches in parallel. Figures 5 and 6 show the proper circuit diagrams for single and double redundant circuits. Test student circuits by picking one or two switches that have “failed” open. The students must then be able to operate the light with the remaining switches. Step Four In this step, students will draw formal circuit diagrams for the circuits that they built in earlier steps. Show them examples of circuit components and their symbols. Example symbols for the components used in this activity are located in figure 1. Additionally, the arrows that have been drawn in each circuit diagram show the conventional flow from + to – as used by many electricians and engineers. This is NOT the same as the direction of charge carrier (electron) flow that is from – to +. Step Five In this step, students will build a complex circuit that includes switches in both series and parallel. Figure 7 shows the circuit diagram for one possible solution. Test the circuit by choosing two switches that fail in either an open or closed position. Students should still be able to operate the light. Discuss with students how redundancy adds complexity to a system, but is necessary. You may also want to add that in a circuit like this on the space shuttle, each switch would also have a sensor attached so that engineers could tell if it failed or was working. This means that a double-redundant system for something as simple as turning on or off a light would have 18 parts instead of just 1!

Battery

Switch (open)

Lamp

Figure 1: Common Circuit Diagram Symbols

Figure 2: The circuit diagram for step 1

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Physical Science

Figure 3: The circuit diagram for a single fault closed circuit.

Figure 4: The circuit diagram for a double fault closed circuit.

Figure 5: The circuit diagram for a single fault open circuit.

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Physical Science

Figure 6: The circuit diagram for a double fault open circuit.

Figure 7: The circuit diagram for a double fault open and closed circuit.

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