Packing a High Altitude Balloon Payload
Below is a set of instructions I used to help some teams launch their balloon payloads in our upcoming HAB flights in Croatia. You might like to consider them a guideline to how you can pack a payload in light weight material for your flight. Of course you can use a Styrofoam box, but that is a bit of an overkill in the world of light weight payloads.
If this helps, then please use the ideas and send us a link on your web page:
Creating your experiment is the hard part, but finding something to put it in can be very difficult too. I have included some idea here that should help. Firstly, let me say congratulations in getting this far. It is great to see so many ready worthy experiments going into the stratosphere.
Let me start this paper by explaining what the out package is meant to do. The balloon will leave the ground and quickly rise in to the upper areas of the troposphere . Here is where jet aircraft fly and if you have ever flown and seen the outside temperature, displayed on the navigation screen, you will know it can get to around -60 C. Hopefully we will only have temperatures of around -50 C. By the time we reach 7km, there is more mass atmosphere below us than above us. In fact way more. This means that the atmospheric pressure is getting very low. At about 20km altitude, we will pass from the troposphere and into the small layer known as the tropopause. Look that up!
The stratosphere is next and it is very warm compared to the temperatures in the jet stream. It may reach -20C or in some places and on some occasions could reach an amazing 5 C. Since the balloon flies with the wind, there is very little force on the balloon during its flight. Even when the balloon explodes, the fall has little impact on the experiments. It is briefly like the “weightlessness” of space. A light foam package may reach speeds of 160kph in the thin air. As the air thickens the parachute slows the payload and we should have a light impact of only around 5m/s or 18kph. Finally what if it lands in water?
So, the main things that we need to combat are:
- Landing impact
A note on batteries. Very cold conditions will cause problems for some types of batteries. Alkaline batteries can be a big problem aand can fail during the flight. We recommend Lithium batteries as these resist the cold very well. They also last about 4 times longer than Alkaline batteries.
Weight is simple, each experiment is meant to weigh only 150 grams, including the packaging, so we are looking for very strong light weight packaging that will fit the size of our payload.
Pressure is less of a problem on the most part. Most things survive pressures close the extremely low pressures of space. We will expect about 1% of the pressure seen at sea level. Pressure does however make it hard to waterproof a payload. Waterproofing usually means sealing things up. That unfortunately will probably create an explosive effect on a large mass of air in any packaging.
Temperature of the payload – or cooling! Heat will leave your experiment quickly and freezing temperatures will probably be experienced at about 3,000m. from then on, your experiment will not return to temperatures above freezing until back on the ground. Check your battery specifications and we have some things that we can do to limit the effects on the battery. More on that later.
Landing Impact is not high. It is easy to cushion an impact of that size. You can run as as fast as that for a short time. The fastest human foot speed on record is 44.72 km/h. The cover still needs to cushion the impact.
Water. We hope to ensure that if it lands in water, we can still recover the experiments. Nothing will keep water out, unless you can make sure that there is no air in the packaging. Then it can be sealed totally. This will be difficult.
Suggestion 1 – Bubble Wrap
Sounds crazy, but bubble wrap can survive in space without the bubbles exploding. It achieves all of the objectives and can even keep water out. it is a good thermal insulator as it has trapped air, it is very light and can cushion impacts as well as floating. It is what I like to use if possible. The electronics for UpLift 16 was wrapped in Bubble Wrap. You can see the wires coming out of the package.
In the above picture, the three wires on the right terminate in a black temperature sensor for the outside air. By keeping it in the shade just beneath the bubble wrap, I was able to measure the temperature of the atmosphere at different altitudes. After landing, it was over 2 weeks before we went to recover the payload and the electronics were intact. In fact we did not even use a parachute. The bubble wrap provided the cushioning for a fall from the stratosphere. It also cause some air braking, slowing the fall. Since the battery was next it the electronics – separated by one layer of insulation tape, the warmth of the payload and the warmth of the battery are used to keep both as warm as possible by each adding to the internal heat. The bubble wrap simply slows the loss of heat.
The one thing to remember when using it is to wrap it three times. Also remember that the bubbles will expand and will apply some pressure to the payload unless loosely wrapped. It should be sealed with a light weight tape.
Suggestion 2 – Food container
Ever had takeaway food in a plastic container? These are very light and strong. If they land hard, they may crack, but that is about it. They are also rather air tight at time. If using these and you do not cut holes for sensors, cameras, wires, etc please remember to add a small hole to allow the air to exit and enter so that it does not blow the lid off the container or crush it. The pin hole will not let in too much water if it lands in a lake, so it will float. You may still need some bubble wrap around the outside, but this is still very light weight. The ones pictured below weigh 33 grams
Suggestion 3 – Paper Towel Roll
These are long and strong as well as light weight. Simply they work well. They are also very light weight – 10 grams. You can tape the ends for both securing the payload and increasing the strength. It is not water resistant, but there is almost no way of protecting your payload for the small possibility the payload landing in water. You can carefully cut the roll to form a smaller holder and lower weight.
Suggestion 4 – Toilet Rolls – Clean and Unused!
Make sure that the roll has not been used in the toilet please! Remove the paper and you will find a short roll about half the size of the paper towel roll weighing about 5 grams. Again, taping the ends will help in securing you payload and increasing strength.
Suggestion 5 – Kitchen and other containers
Look around the kitchen, the bathroom and almost anywhere in your office or home there are a variety of containers. Here are two more:
One is a cotton bud container weighing 20 grams – small but very strong. The other is a fruit container without a lid. You can cover the top with a rectangle of thin plastic – ensure air can escape. The cotton bud container weighs 20 grams and the fruit container weighs also weighs 20 grams but is very large in comparison.
It is important to ensure a secure electrical connection if using electronics. We suggest that all connections be soldered and also make sure that switches are not easily “knocked” to the off position. This can be easily achieved by cutting the top off a lever type switch – even a tiny ones. This means less of the lever to get in the way as well as less leverage. Similarly there are other switches such as slide switches. These can be accidentally knocked too. You can cut these down too. We can use a screwdriver to slide the switch as directed in your instructions. You can also go to your electronics shop and get a switch that may need a screwdriver to operate.
We can also suggest that you tape the switch to the “on” position so that it cannot be accidentally switched off if bumped during packing or during flight.
Alternatively, use a Plug and socket. these are robust. Below is a picture of a battery pack with a connector ready to be plugged into the payload.
These are small and very light weigh.
A few final tips:
- Write your full details on a label on the payload.
- Use a waterproof pen on the container.
- We suggest that you use Lithium batteries and thermal insulation to keep your batteries (and possibly the payload) from freezing.
- Have fun creating your experiment.
- Stand back – we are doing science!
As I said at the start, these are a few ideas for students participating in Team Stellar’s Stratospheric Balloon flight / Balon Stratosfera. I hope that some of this helps with your own balloon projects.