To begin our journey of launching a weather balloon, I started with a quick YouTube search of “weather balloon launch” leading to over 17,000 results. I was amazed at the incredible footage and especially by what people sent to the stratosphere: paint balls, marshmallows, action figures, bacon, crickets, beer, and even a hamburger! You can check out the footage of the “10 Weird Things Humans Have Sent to the Stratosphere” here.
My involvement with the weather balloon launch is part of my job as a STEM Project Director with Communities In Schools of San Antonio. I manage several after-school space and robotics programs for middle school students. At one school, over 50 7th and 8th graders meet each Friday afternoon to discuss a science topic or work on a project. This year, the big activity was a weather balloon launch, and the students have been researching and preparing since October. The program is led by 2 science teachers and myself, and it has been a wonderful experience!
To first introduce the project to the students, we played several videos for inspiration. As I mentioned, almost everything you can think of has been launched, and here are some of my favorites:
- Hello Kitty in Space
- Toy Robot in Space
- Rubber Chicken in Space
- Paint Balls in Space
- Mission to Space- Full GoPro Flight With Arduino & DIY Payload
We also showed these awesome clips of humans jumping from the edge of space:
- Felix Baumgartner's supersonic freefall from 128k' - Mission Highlights
- Alan Eustace - Record-Breaking Near-Space Dive Leaps from 135,000 Feet
Now that the students are excited, the first order of business was to understand the mechanics of the launch and all the components involved. I presented the information through asking students their initial thoughts on topics such as “Why does the balloon float” or “How high will the balloon go” followed by a discussion of the answers. Important topics to address:
Why does the balloon float?
The latex balloon floats once it has filled with an appropriate amount of helium, a gas that is less dense than the air in our atmosphere. In other words, as long as the weight of the helium plus the balloon latex is lighter than the air it displaces, the balloon will float. This can also be explained in terms of a buoyancy force pushing upward becoming greater than the weight of the balloon and helium. A simple animation that shows this can be found here. The concept of density can also be explored with helium having less density than the atmosphere’s main gases of nitrogen and oxygen. Bottom line: we need enough helium to provide enough buoyancy force to lift the payload.
What happens as it moves upward?
As the balloon reaches about 100,000 feet, it will pop! Why? As the balloon journeys upward, it will experience less and less pressure. This causes the helium of the balloon to expand and stretch the latex skin of the balloon. For a deeper understanding, you can introduce the ideal gas law equation (PV=nRT). When balloons rise in the atmosphere, the surrounding temperature decreases and the pressure decreases, so according to the ideal gas law equation, the volume must increase to compensate for the change. And then what happens? The volume continues to increase until a balloon initially 6 feet in diameter stretches to 30 feet and bursts!
How will we retrieve the balloon?
After the burst, the remaining payload will start to plummet back to earth. Without anything to break the fall, everything would hit the ground at a terminal velocity of 124 mph! Such a speed would destroy anything in the payload, so a parachute is used slow the descent. It is attached in such a way that the flight train keeps the parachute shut during launch, but when the balloon bursts and the air rushes past the parachute as it falls, the material will be forced open and slow the fall. A second part to this question is actually finding the balloon. The payload can travel quite a distance, so a reliable tracking device must be installed.
Is it legal?
Yes! The flight of unmanned balloons, rockets (including fireworks), and kites are all governed by the Federal Aviation Administration (FAA) through Federal Aviation Regulations (FARs) Part 101 Subpart A. The most important safety practices are:
- When it comes to tracking the high altitude weather balloons when in flight, no one should use a cell phone for that purpose.
- Payloads should not exceed the 3 ounces per square inch of package weight to size ratio.
- The maximum weight for any payload package is 6 lbs.
- The total weight of all the payloads, the weight of the balloon not included, should not exceed 12 lbs.
- The rope or cable used should not require more than 50 lbs of force to separate the payload packages from the balloon.
- The launch should not create any hazard to other people and property.
- For safety reasons, no one should use high altitude weather balloons to drop objects such as gliders and projectiles.
As stated above, there is a weight limit to follow these conditions. The 6 pound limit per payload will be a key engineering constraint that will impact the equipment on board and any extra materials students want to include.
After this introduction and background information, the fun part begins with designing and building the payload! Next post will describe how our students went from concept to final launch.