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Add the Micro to Gravity!

Information for Teachers and Parents

This page provides information on how to engage your students in the PSA Microgravity Challenge and ideas for possible solutions to the challenge. You may implement one of the solutions we provide, or come up with your own ideas. We encourage you and your students to engage in the design process and come up with your own creative solutions.

The Personal Satellite Assistant (PSA) is a small round robot that is being designed to float in the microgravity environment of the International Space Station (ISS) and help the astronauts with their chores. If your students are not familiar with the PSA, have them go to the PSA Education web site to research information on this robot. If you do not have Internet connections in your classroom, print pictures of the PSA and the ISS. Discuss with your class the purpose of this robot that is being designed and built at NASA.

We encourage students to work on the challenge in teams and follow the steps in the design process:

A. Define the problem
B. Generate ideas
C. Test the ideas/solutions
D. Modify the solution
E. Present the results

Define the problem

Here are the basic requirements for the challenge:

  1. Use a tennis ball for the PSA, with an approximate diameter of 6.5 cm and mass between 55 and 60 grams. The tennis ball can be new or used and of any color.
  2. The PSA must be suspended by some device and stay in the suspended position without being held by a person.
  3. You must be able to move the PSA (manually or mechanically) 3 inches up or down to a new position and have it remain in that new position. Your PSA cannot roll.
  4. You must be able to push or pull the PSA and have it keep moving (after you have finished pushing or pulling it) for 3 seconds.

Discuss each of these requirements with students and have them restate and write the problem in their own words so you know that they understand the requirements.

Generate Ideas

Have students brainstorm and discuss their ideas. Here are some of our ideas:

Attach strings, straws, wires or anything else to your PSA, then hang your PSA from one or more balloons, attach a pulley, or a use an equal-arm balance. Students may want to construct a type of mobile. You could immerse your PSA in water and weigh it down with something. Every idea will have drawbacks - there are pros and cons to every design. Students should understand this and come up with ways to minimize the drawbacks. There is no perfect design.

Test the Ideas or Solutions

Have students pick one or more ideas to test. The whole class can test one idea or each team can test a different idea. When you test an idea, remember that requirements 2, 3 and 4 must be met.

If you use the balloon solution, consider asking students to calculate how many balloons they would need and of what size. You might want to have them think about the forces involved. The force of gravity acts downwards on the PSA, so the balloons must provide an equal upward force. Students can also use trial and error to find the size and number of balloons. Instead of using the tennis ball for testing, use a polystyrene (similar to Styrofoam™) cup and add pennies to it till it reaches the weight of the PSA/tennis ball. Remember that you should be able to move the PSA up or down and have it stay in that position. A string may be too flexible for requirement #4. You may need to use something rigid like a straw or piece of lightweight metal or plastic.

You could attach a pulley to the PSA, or hang the PSA from an arm of a balance. A suitable weight must be selected to balance the PSA and it must be able to move vertically up and down. You can find equipment for this in a school physics lab, or ask if a student has a toy construction kit that you can use. Pulleys can be created with strings, rods and wheels. Students may discover how an equal arm balance works. The fulcrum is the point at which the arm balances, and a lighter weight must be placed farther out, away from the fulcrum, to balance a heavier weight closer to the fulcrum.

You could immerse your PSA in water. You will need to attach a weight to the PSA. Instead of attaching a weight, you could punch a small hole in the PSA and put sand or some other substance inside it. Simply weighing the PSA down will not enable you to meet requirements #3 and #4. Students can learn a lot about buoyancy in this exercise.

Keep in mind that there is no perfect solution, and part of the design process is figuring out how to minimize the disadvantages of a particular solution.

Modify the Solution

Have the class share their tests and results. You can use the forum/chat room to discuss your solution and ask for advice. Another team may have solved your problem and may be willing to share their solutions. Sometimes it is helpful to simply see what did not work for others and why.

Have the teams come up with modifications to their solutions. They may decide to test using helium balloons instead of air, or try a water solution after having tested in air. Have students test and modify their solutions as many times as the schedule allows.

Present the Solution

Take a digital picture of your solutions and send them in to lconrad@mail.arc.nasa.gov. Include a written description of how the problem was approached, the tests that were carried out and the modifications that were made, and why the eventual solution was chosen. More information can be found here >>


If some students come up with a solution they are satisfied with and want to do more, ask them the figure out:

  • What happens to the setup if the weight changes, for example, if gas leaks out of the balloons, or some substance leaks out of the PSA? How would you modify your setup to account for this change?
  • This challenge looks only at the up and down (vertical) movement of the PSA, since the force of gravity acts in that direction. Suppose we wanted the PSA to be able to turn as well? How would you modify your setup to enable the PSA to turn?
  • Ask students to consider the difference between their solution and conditions on the ISS. Tests are conducted with prototypes in simulated situations. How is the real situation different?

Helpful Links

Learn more about microgravity >>
Education standards >>


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