If you want to find out what happens as you go from the Earth's surface up to the lower mesosphere, this is the project for you! Here, we'll show you how you can configure a simple weather station for launch in a weather balloon up to around 100,000 feet. This builds off of a previous Instructable which shows you how to build a basic weather station which logs to an SD card with a few Adafruit sensors and an Arduino. It's a good starting place and we recommend building it here. Once you've done that you can make a few changes and you'll be ready to gather data as your balloon disappears into the sky!
Our mobile station is equipped with the original contents of our station (minus the anemometer): an Arduino wired to a protoboard with a data logging shield, a DHT22 Temperature and Humidity sensor, and a BMP280 barometric pressure and altitude sensor. In addition to this, we added 2 cameras, different housing, and a few other extras which allow us to protect all of our sensors and cameras.
Note that this is not a guide detailing how to launch the balloon itself, but rather a guide on how to build the case that you launch along with the balloon.
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Step 1: Gather Materials
Start with a simple weather station such as one here with humidity, temperature, pressure, and wind sensors which log to an SD card all contained in a waterproof casing. **Note that it is important to use a 9V battery with the Arduino to power the circuitry. Since ours ended up dying early, we think that better insulation would be needed for extended data collection (although a larger power source could also be helpful).
For our purposes here, we'll need to disconnect the anemometer and remove our materials from the waterproof casing.
In order to modify what's left to fly up into the lower mesosphere, you'll need a few new materials:
- Styrofoam or similarly light and insulating box for circuitry
- Hand warmers
- Tape, preferably something durable such as duct tape
- GPS tracker, such as the Spot Gen 3 Satellite Tracker with subscription
- 2 cameras with video capability and long-lasting batteries or extra battery pack (we used a GoPro Hero 4 with EcstaPro battery pack and an Akaso EK 7000)**
- Defogging spray for the camera housing
- Our Akaso EK 7000 fogged up due to the hand warmers
- 64 GB SD cards (our Go-Pro ran out of memory a little before the balloon popped, and we had a 32 GB)
- 50lb String
**Make sure that the SD cards in your cameras have sufficient memory for multiple hours of footage. Also, it's a good idea to find the settings that will minimize the rate of battery drain on the cameras so that they film for as long as possible.
We used a 6"x8"x10" styrofoam box with small compartments (pictured here) to make it easy to balance weight, insulate, and protect the sensors, but this is by no means the only option.
**Our Go-Pro lasted until the memory on the SD was full, so we had no issues with a lack a battery power. Our other camera only got about thirty minutes of footage, and we think that the changing temperature on the ascent sapped the battery. It is unclear wether better insulation or an additional battery pack would be sufficient to solve this problem.
Step 2: Make Circuitry Durable
Your case is going to get buffeted by wind on the way up. It will then hit the ground at about 5m/s, so you need to make sure your sensors are securely attached to your protoboard. You'll also need to ensure that the temperature sensor is outside of your casing. This will allow it to record the actual conditions of its position, instead of logging the conditions inside the box, where there are heat warmers to keep other circuitry and cameras running.
Step 3: Arrange Within Casing
If you're using styrofoam, cut out holes in the case for your cameras. If using the Spot GPS tracker (Gen 3), make sure that it is antenna side up to be sure that it transmits coordinates. Configure everything so that you can easily add hand warmers near the circuitry, pressure sensor, and cameras. If you're not using a box with cutouts, use either padding (such as cotton balls) or some other structure (like cardboard sheets) to keep everything from moving around or getting knocked into a less optimal position. Just before launch, add hand warmer** to keep circuitry working with full capacity. Consider adding defogging inserts to keep the cameras from fogging as the temperature changes.
**An issue that we faced was the failure of our electronics. Our circuit/data logger cut out very early into the launch, and we didn't end up with any good weather data. Testing the function of the circuitry at different temperatures and finding better methods of insulation will be critical to get this component to work. We simply didn't have time to try again.
Note: Make sure that you don't turn on your cameras / connect anything to the battery until just before launch. The batteries on the cameras will just about last through the flight if you have an extra battery pack, but you don't want to start them before you have to.
Step 4: Prepare for Launch
There are a few things left to do before launch! For one thing, you'll need to either buy or build a radar reflector. This device will reflect radar signals sent by planes, allowing them to see that something is in the sky. Because we wanted a very lightweight reflector, we decided to build it ourselves. All you need is aluminum foil, cardboard, and tape! A link to the Instructable that we used as our template can be found here.
We used a 600g balloon from High Altitude Science and a 5 foot Rocketman parachute, which was perfect for our payload size.
You'll also need to run simulations of your balloon flight to see where it's likely to land and how much helium to use. To calculate our helium needs, we used this site. For our balloon, we needed about 80 cubic feet of helium. This also allows you to determine lift, ascent rate, burst altitude, and flight duration. Once you've done that, use one of thesesites to determine the trajectory of your flight. These simulations are remarkably accurate, and they will let you decide when to launch so that you can retrieve your balloon with minimal fuss.
However, note that if you don't have a good way of measuring the lift of the balloon during launch, you'll only be able to make vague estimates of when it will burst and how far it will go. Our balloon ended up going considerably farther than expected, which landed us in a spot of trouble when it landed in a military base.
Step 5: Launch the Balloon
Time for launch!
We used a tarp to make sure that our balloon wasn't directly on the ground for launch. Make sure that you've got a wide open space for launch and that you aren't too close to tall towers or mountains that your balloon could get caught on.
Step 6: Recover the Balloon and Enjoy the Film!
Here is a little clip we got from our balloon. This is over Big Bear Mountain, Big Bear Lake, and the San Gorgonio Mountain peak (which is 11,000 feet high). We estimate that our balloon reached between 90,000-100,000 feet before it popped. We used the angle of the camera lens and the distance between two points in the video to estimate the vertical height of the balloon.
So, we wish anyone else luck who takes on this endeavor. Let us know how it goes, and share some of the amazing film you get!