• String
• 2 foam balls (3-inches [7.6 cm] in diameter)
• Cellophane tape
• Masking tape
• Yard stick and or tape measure (groups can share)
• Protractor (the bigger the better; groups can share)
• Scissors

For helpful background information on how engineers navigate satellites and on the International Space Station, please see the related lesson plans “Not So Lost in Space,” and “Life in Space: The International Space Station.” Also helpful is the Smithsonian Earth From Space online exhibit.

Introduction/Motivation

The International Space Station (ISS) is a very large satellite that orbits the Earth. It is 3,300 sq. ft. in area, and moves in an almost circular low-Earth orbit, about 250km above the surface of the Earth. In this activity, students will learn how to predict and track the ISS’ path using special computer software and how the paths of spacecraft and satellites can be calculated and accurately predicted. Using Skywatch and STSPlus, online tracking software, the unimaginable can be done. To create these programs, you need a college degree in Aerospace Engineering. But, fortunately, middle school students just need access to a computer to use these programs.

Three key terms used in this activity are:

Azimuth – the number of degrees measured clockwise from the northern horizon. An object at 90 degree azimuth is due east. An object at 270 degree azimuth is due west.

Elevation – the height of an object, measured in degrees above the horizon. An object directly overhead is at a 90 degree elevation. An object on the horizon is at 0 degrees elevation.

Range – the distance from where you are located to a spacecraft or satellite.

Other keywords: navigation, space, orbits, satellite

• Gather the materials and equipment needed.
• Run the Skywatch program and pick a day within the next week or so for the students to find and track the ISS. Become familiar with the software before showing it to your students. See Troubleshooting Tips for more details.
• Mark a point in the center of the room that will represent your city. Using masking tape, mark a line pointing north from the city point.

• Click on Start Java Applet.
• Enter your city (or closest city) under Observer Location.
• Notice how Skywatch automatically adjusts to your latitude, longitude, and altitude.

2. Click on Next Sighting to track the next observable path of the ISS.  You may have to click Next Sighting more than once if it is more than 1 week away.

3. Find the day, or night, of interest and have the students print out the predicted points of travel by hitting the Print button.

4. Ask students what questions they have about the print out.

5. Assign each group a different point to model. One group at a time can model the ISS around the city point.

6. Each group should cut a length of string corresponding to the range scaled down by 10 and in inches. For example, if the range was 749 miles, the string would be cut to 74.9 inches long.

7. Have one student in the group hold one end of the string to the city point while a second student holds the other end along the ground facing north. The second student should always have the string pulled tight.

8. The first student should direct the second student to move clockwise around the city and stop when the azimuth is met. For example, if the azimuth is 180°, the second student will have moved in a half circle and be directly south of the city point.

9. Next, using a protractor located at the city point, the first student should instruct the second student to raise the string until the elevation is met.

10. While the second student carefully holds the azimuth and elevation, a third student should measure and record the height and location of the end of the string. This can be done by taping a piece of paper on the ground under the end of the string, marking an X beneath the end, and writing down how high it was next to the X.

11. Finally, when all the groups have marked their Xs and heights, the teacher or designated students should hang a foam ball over each X according to its height. In the end, you should have a 3-D model of the ISS path.

12. Ask two groups to volunteer to present the model to the rest of the class.

• How could a satellite track be traced without computer software? (Possible answers: Extremely hard to track them, manually, with other satellites sending data to a central office.)
• Why do mission managers and engineers want to track satellites? (Possible answers: to predict when they will fall to Earth; to make sure they remain in their correct orbits.)