### Overview

In this activity, students will design a balloon and gondola system capable of supporting weight. Students will then determine the mass needed to cause the balloon to ascend at a given rate, descend at a given rate, and/or maintain a constant altitude over a set period of time.

### Management

• Have a few extra helium balloons in case some pop.
• Keep the activity indoors to prevent balloons from floating away and contributing to ground and water pollution.
• Consider taping measuring strips against a wall or flat surface so students can see their balloon’s altitude.
• Older students may calculate the buoyant force (see Extensions) before testing to determine the mass needed for the challenge(s).

### Background

When people think of NASA, they don’t usually think of balloons. However, NASA’s Balloon Program Office at Wallops Flight Facility in Virginia has been launching balloons since 1983. The Balloon Program Office launches 10-15 balloons a year from locations around the world for technology development, scientific research, and education purposes.

This illustration shows a balloon ascending into Earth's upper atmosphere while carrying a small scientific device. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab/Michael Lentz | + Expand image

Balloon missions are not only cheaper to operate than space missions, but they also take less time to plan and develop than space missions. Because of this, they can use higher-risk new or state-of-the-art technologies that haven't yet flown in space.

Helium balloons float thanks to the buoyant forces outlined in Archimedes Principle, which states:

Any object, totally or partially immersed in a fluid or liquid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

In the case of balloons, the fluid they displace is air. Because air is heavier (more dense) than helium, the buoyant upward force pushing on the balloon is stronger than the gravitational force pulling down on the gasses in the balloon, which causes it to float. (In this case, the weight of the balloon is negligible and does not stop the balloon from floating up.)

NASA’s Balloon Program Office currently uses two different types of balloons to lift payloads into the atmosphere: zero-pressure balloons and super-pressure balloons. Both types of balloons are made of thin plastic film, called polyethylene, with a thickness similar to that of plastic sandwich wrap. Zero-pressure balloons are typically used for short-duration balloon flights (a couple hours to a few days), while super-pressure balloons are required for long-duration flights (up to 100 days). For more information on these balloon types, visit NASA’s Scientific Balloons site.

NASA’s use of balloons varies. In 2014, the agency used a balloon as part of a project designed to test Mars landing technology. The project's Low-Density Supersonic Decelerator was lifted to an altitude of 119,000 feet (36,270 meters) by a balloon, then boosted by a rocket to an even higher altitude, where the environment is similar to Mars' thin atmosphere.

Ian Clark, principal investigator of the Low-Density Supersonic Decelerator, gives a play-by-play of NASA’s 'flying saucer' Test in Hawaii, using high-definition video shot from cameras on board the test vehicle. Credit: NASA/JPL-Caltech | Watch on YouTube

In 2019, the first detection of an earthquake from a balloon was made using sensors floating about 16,000 feet (4.8 kilometers) high. In the future, NASA hopes to use balloons floating in Venus' atmosphere to detect quakes – something that can’t be done on Venus’ incredibly hot, high-pressure surface.

In 2024, NASA plans to launch a stratospheric balloon-borne radio-telescope called ASTHROS, or Astrophysics Stratospheric Telescope for High Spectral Resolution Observations at Submillimeter-wavelengths. Lifted by a 400-foot (120-meter) diameter helium balloon, the mission will spend three to four weeks floating about 130,000 feet (40,000 meters) above Antarctica, observing star-forming regions of the sky in far-infrared light as well as planets forming around newborn stars.

In this one-hour education webinar, NASA experts discuss infrared astronomy and the ASTHROS mission, a balloon-based telescope that will study star-forming regions in the Milky Way galaxy in far-infrared light. Credit: NASA/JPL-Caltech | Watch on YouTube

The Balloon Program Office, in collaboration with other NASA centers and private industry, continues to investigate the feasibility of balloon missions on other planets and space bodies as well. Possible NASA missions of interest are targeted for Mars, Venus, and Saturn's moon Titan, where balloons could enable measurements at different altitudes that are currently not feasible with other platforms such as satellites, landers, and rovers.

### Procedures

1. Tell students they are going to simulate a scientific balloon mission by designing a balloon and gondola system that will ascend or descend at a designated rate or maintain a steady altitude while supporting mass in a container.
2. Share some images of scientific balloons and describe some of the ways NASA uses or plans to use high-altitude balloons as described in the Background section.
3. Ask students to describe the forces they will have to consider while completing the challenge(s). Explain terms (e.g., gravity, weight, buoyancy, lift) as necessary, depending on student knowledge.
4. Consider having older students complete the force calculations as described in the Extensions section.
5. Have students sketch their balloon design. Credit: NASA/JPL-Caltech | + Expand image

Have students choose the mission they would like to complete. Credit: NASA/JPL-Caltech | + Expand image

Have students build their balloon and gondola system. Credit: NASA/JPL-Caltech | + Expand image

Have students test their predictions. Credit: NASA/JPL-Caltech | + Expand image

Have students record the mass of their gondola. Credit: NASA/JPL-Caltech | + Expand image

6. Have students come up with and sketch a design for their balloon and gondola system that uses string, tape, a cup and a balloon. Remind them they will need to design a way to hang their gondola from the balloon so that it will support items placed inside it.
7. Ask students to predict how much mass in kilograms (or how many of a certain item) will be needed to accomplish one or more of the following challenges:

• Maintain altitude: Students must find the appropriate amount of mass to place in the cup that will cause the balloon to float and maintain a steady altitude of approximately 3 feet (1 meter) for 30 seconds. (Fb = Fg)
• Controlled ascent: Students must find the appropriate amount of mass to place in the cup that will cause the balloon to ascend at a rate between 10 and 20 inches per second (0.25 to 0.5 meters per second). (Fb > Fg)
• Controlled descent: Students must find the appropriate amount of mass to place in the cup that will cause the balloon to descend at a rate between 10 and 20 inches per second (0.25 to 0.5 meters per second). (Fb < Fg)
8. Students should build their balloon and gondola system according to their design and place several items in the gondola as it hangs from the balloon to ensure the items stay inside. Students should adjust their design(s) as necessary to ensure they can support items placed in the gondola.
9. Once a stable design has been developed, students will add objects to the gondola in order to successfully complete their selected challenge(s).

• Tape a meter stick against a wall, or put height markings on the wall that students can use to measure the height of their balloons.
• Students can use a stopwatch to measure the time it takes to ascend or descend and calculate the rate (centimeters / seconds).
• Students can also use a mobile device to record their balloon’s ascent or descent and calculate the rate using timing information from the video file.
10. Students should record the mass (or number of items held by the gondola) required to successfully complete their challenge(s) and then compare it to their prediction.
11. See Extensions for additional steps involving force and acceleration calculations.

### Discussion

• What did you observe? How did this compare to your expectations?
• If you completed more than one of the challenges, compare the forces acting in each challenge.
• Draw a Force Diagram that describes what forces are acting on the balloon and the mass in the gondola.

### Assessment

• Student designs should support the gondola hanging under the balloon with the gondola holding the required mass.
• Students should be able to determine the mass needed to maintain altitude, control descent rate, and/or control ascent rate.
• Students should be able to measure the appropriate times and calculate rate, as needed.

### Extensions

1. Calculate the approximate buoyant force being exerted on the balloon.

Fg = mg
Fb = pgV
Fg - force of gravity (N)
Fb - buoyant force (N)
m = mass (kg)
p = density of fluid (air ~ 1.225 kg/m3)
g = acceleration due to gravity (m/s2)
V = volume of object

If students are unable to accurately measure the volume of the balloon, have them measure the small diameter and assume a spherical balloon shape.
2. Calculate the acceleration of the balloon as it ascends or descends. Remember that acceleration is the change in velocity over time. Students may need to use technology, for example, to record the motion of the balloon over time, to first calculate their velocity, and then how the velocity is increasing or decreasing per unit of time.