Building and Testing (part 2) - launching a High Altitude Balloon

Author: Jacob Smith -

Welcome to part 2 of 'Building and Testing' - things are getting even more exciting now!

The payload box

Once I had successfully tested the tracker and cameras, next on the list of things to do was to create something to safely carry them up on the balloon! A polystyrene box is by far the most common method of housing the components due to its low weight and good insulating capability, so this is what I went for.

The most important thing when fitting the components is to make sure they are really secure because one, you don’t want cameras moving around during flight, and two, landing speeds can be about 10mph. So with this in mind I created a layer of polystyrene with cut outs into which the components would snugly fit. I will also secure them with cable ties just before launch. You can see this layer in the top right of the right hand picture below.

Using a spare polystyrene box I practised cutting different shapes and angles for placing the cameras. I spent the day making a huge mess…thankfully it was in my parents’ garage, but I still had to clear up! You will notice in the final arrangement below that the cameras are angled slightly down from the horizon which I hope will make for better images. What I didn’t think of though was that I have ended up with an unbalanced payload with a lot of the mass on one side. To account for this my Dad came up with the great idea of using different length lines on each corner of the box that attach to the balloon, hopefully making the box level for flight.

Field testing

With the payload box complete my Mum and I took the box and tracking equipment to the park to play an alternative version of ‘hide and seek’. In the middle of a field I set up a tracking station, using my antenna and tracking software on my laptop to track the movements of my mum carrying the payload box. We put the box in a bag just so we could easily attach a bamboo cane to give some elevation to the tracker, as theoretically it needs line of sight to the radio receiver to work (it wasn’t just to make people give her weird looks!)

You may notice something on the underside of the box. This is a ‘1/4 wave ground plane antenna’ that is needed to transmit the radio signal over large distances. In English, that’s a main radiating element that points down towards the Earth with four ‘radials’ at right angles on the bottom of the box to reflect the signal equally in all directions. ¼ wave just means the length of these elements is ¼ the length of the radio wavelength at my transmitting frequency. It was quite simple to make and what you can see are the blue straws that I placed over the elements to keep them relatively straight. In the previous picture of the payload box you can see the other end of the main radiating element cable coming up through the bottom of the box and plugging in to the tracker.

The moment of truth

So, to the game of hide and seek…It took a short while to set the frequency and bandwidth of the radio software that allowed me to correctly receive the radio transmission from the payload tracker, but soon enough I was decoding the data into location coordinates. I then asked my mum to walk to the end of the field, and I was still able to get the signal. A good start. As she moved around I was fully decoding about one in two transmissions, losing some data when she went over a hill or past buildings. However, I learnt how to alter the parameters in the radio software that allowed me to increase the signal strength again which will be very helpful for the actual flight.

My mum then kept walking, and walking, and walking…eventually stopping and challenging me to come and find her. Having picked up signal I accepted the challenge, packed up my gear, headed out the park, and found her! All these successful tests left me amazed with what I had created, and much more confident about the final balloon flight.

Next steps

I’m getting much closer to being ready for launch. Now that I have finalised my components and successfully tested them all I can start looking at choosing the correct size balloon and parachute for my payload. I will also start researching and buying all the other things that will be needed for the launch day, most importantly finding a Helium supplier. By the time of writing my next post I hope to have the launch organised so I can describe how it’s going to go, and then it will be fingers crossed…stick around as we get to the most exciting part!