High Altitude Balloon – Success!

Introduction

I remember vividly picking up a copy of MAKE magazine and being captivated by an article on building a high altitude balloon (HAB). For years, I had wished there was some project I could undertake as a hobbyist that would give me a glimpse into space. While a HAB doesn’t reach the altitude technically considered space, they can reach altitudes in excess of 100,000 ft, allowing you to see the blackness of space and the Earth’s curvature.

The project turned out to be much more complex than I thought. Designing electronics that could withstand the extremely cold temps at that altitude required keeping everything in an insulated enclosure. How do you track something 100,000 feet in the sky? What happens if the balloon doesn’t pop? How dyou recovery it? Where will it land? These are all questions that needed to be answered before I could launch the balloon.

Payload

In the Fall of 2014, I finally launched the balloon in a remote part of Wisconsin. The payload included a high definition video camera, a Geiger counter, and internal and external temperature sensors. Below is a picture of all the payload electronics integrated onto a prototyping board. An Atmel microcontroller was responsible for collecting data from the experiments and recording them to an SD card.

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Tracking

Figuring out the tracking of the balloon was the most difficult part. I had invested a lot of money into this project and wanted to make sure that I didn’t lose all my hard work and money. Since I already had a HAM radio license, I decided that APRS tracking was the best solution. Below is the tracking setup. It consisted of a cheap handheld radio, a GPS receiver, and the OpenTracker from ArgentData.

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The OpenTracker’s job was to take the signal from the GPS and convert it to an audio signal which would be fed into the radio and transmitted. The signal would be picked up by any nearby APRS stations and uploaded to aprs.fi, where I could track the balloon online. In case there were no APRS stations nearby, I had a mobile tracking station so I could manually track the balloon myself.

Launching

I used an online balloon flight prediction service to help me choose a day to launch the balloon. It was essential that I launched on a day with minimal winds to avoid having the balloon drift into Lake Michigan.flight_prediction.png The biggest obstacle on launch data was dogs. I chose to launch from a remote park in the countryside. Someone decided to bring their two rambunctious golden retrievers and let them out while I was filling the balloon. Luckily, disaster was narrowly avoided. Considering the tank of helium alone was over $150, I was relieved!

After filling the balloon, it was released to embark on its stratospheric journey. Below are a few pictures from filling and launching.

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Recovery

Recovering the HAB payload proved to be extremely difficult. At first, the signal had cut out so we didn’t really have any idea where it landed. After some time, the signal was picked up by a nearby APRS beacon, providing us with a reasonable estimate of where it landed. Unfortunately, the payload happened to land in an area surrounded on three sides by an artificial canal. After knocking on some doors, we were given permission to go bank in the woods and recover the balloon. It took over an hour to locate the payload but we finally found it in some very dense young forest.

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Results

Here is the video recorded by the HD video camera on board the HAB.

Below are some graphs of the sensor outputs as well as some snapshots from the video camera.

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temp vs alt.png
Note how the external temperature rises once the balloon reaches 60,000 ft (18 km). This point is the end of the troposphere and the beginning of the stratosphere. This is due to the increased ozone concentration which absorbs UV light from the Sun and re-emits it as infrared.

temp vs time.png

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The microcontroller output the total number of ‘clicks’ from the Geiger counter every few seconds. This plot shows that number over time.
rad_rate.png
Plotting the derivative of the Total Radiation Count vs. altitude shows an interesting trend. Once the balloon reached the stratosphere, the radiation count skyrocketed. Since the Geiger counter I used was able to detect only alpha and beta particles, the increased radiation count at higher altitude is likely due to interaction of UV rays with the atmosphere creating these byproducts.
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Altitude is approximately 15,000 ft
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Altitude is approximately 40,000 ft
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At maximum altitude – 82,500 ft
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The balloon track downloaded from the APRS website
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