How to Launch a School Weather Balloon
In May 2013 we sent a weather balloon into the stratosphere, carrying a digital camera and GPS tracker so that the camera could be retrieved when the balloon came back down to Earth. We got some amazing images of the Earth and its atmosphere.
Here are some basic instructions if you want to have a go!
What do you need?
Weather balloon: These are very easy to come by, as a quick internet search will show. The bigger the balloon, the heavier the payload you can put on it (ours was a 350g balloon for use with a payload that weighed 540g). The more gas you put in the balloon, the faster it will rise but the lower it will be when it bursts. You’ll also need helium to inflate the balloon. You can calculate how much, once you know the size of balloon, weight of payload and how high you want it to go, on a website such as habhub.org – use the burst calculator. The typical cost of a balloon is around £50 and helium will cost around £20.
Digital camera: The lighter the better. You’ll need to check that the camera stays on, recording for at least 2 hours. The camera will need to withstand temperatures around -50C for about an hour. Even though the camera generates heat, you will need to insulate it – for example in a polystyrene box with holes for the lens. Test it in the freezer! Think about which way you want the camera to point – up to see how the size of the balloon changes, sideways so that you get nice images of the Earth’s curvature and atmosphere, or down to get good images of the Earth. We used a camera with a fisheye lens to maximise what we saw. It cost around £70.
GPS tracker: To help you find the payload once it has come back to Earth, this sends signals to a mobile phone. You will need to include the cost of buying credits – these let you contact the tracker and find out where it is. Our tracker cost around £100 and weighed 58g. The tracker is out of range while it is high up in the atmosphere, so you won’t get a complete track of where your balloon went from it.
CAA permission: You must have CAA permission before launching a weather balloon, as the balloon will almost certainly go into controlled air space – just think of the damage it could do to an aircraft. This should be obtained at least 28 days before the launch but, as the weather forecast will not be known that far in advance, you can specify a window of a few days. The CAA issue a NOTAM to air traffic. To obtain permission, contact the CAA on 020 7453 6599 or email AROps@caa.co.uk. The maximum weight of the payload must not exceed 4kg (but you’ll probably want it substantially less than this to maximise how high it goes).
We also included a radiosonde. This is the bit of kit weather observers use to measure temperature, humidity, pressure and velocity as the balloon travels through the atmosphere. However, it can only be used in conjunction with a receiving station – only people like the Met Office and some Universities will have one of these. Simpler instruments could be used instead.
A parachute so that the camera doesn’t come down to Earth too fast. This needn’t be much more than a circle of plastic and some nylon cord. The brighter the parachute, the easier it’ll be to find. Our parachute also had a circle of wire beneath it to keep the parachute open, which we strapped the payload to.
Do you also have or need public liability insurance?
What else will you need to do?
Check the weather forecast!
You’ll get the best images of the Earth if its not too cloudy. If the launch is going to be a public event, you don’t want it to be raining. Also, it can be hard to launch a balloon in windy conditions.
Importantly, you’ll want to make sure that the balloon lands somewhere you can retrieve it before the tracker runs out of battery – not too far away, and not in the sea! To have a look at a trajectory forecast, go to habhub.org and enter your launch site details. Most weather balloons rise/ drop at 5m/s but you should check the specifications of the balloon you have bought. Your CAA permission may well specify which way the wind should be blowing for the launch to go ahead, to avoid major flight paths. When calculating how much helium to put in your balloon, you want to maximise the height the balloon will get to, but minimise the length of the flight (so that it hasn’t got time to travel too far from the launch site). There are some times of year – when the jet stream is usually over the UK – when the balloon is likely to travel further than others.
Remember that the forecast will get more accurate the closer you get to launch date.
Your school may be in a location where you are very unlikely to be able to get CAA permission (e.g. if you are close to an airport) so that you have to consider launching from elsewhere.
Science Tasks: As well as sending a camera and GPS tracker up with the balloon, something fairly light can be sent up as well. This is an ideal opportunity for a science project. You could send up instruments to measure temperature, pressure etc. or you could test a design – could you protect an object from the cold temperatures in the stratosphere (in which case you’ll need a max/min thermometer in there too), or from the extra UV in the atmosphere, or from the impact on landing and general buffeting on the way up?
Some information about linking a balloon launch to the primary science curriculum from Jon Chippindall.
YouTube film of the highlights of our balloon launch with camera footage and the measurements the radiosonde made.
Here is a trajectory forecast activity suitable for a science club preparing a balloon launch.
A lovely balloon launch activity with data from Discovering Antarctica.
An article from Catalyst magazine about the balloon launch.
Balloon news – a website for people launching weather balloons.
A mini temperature logger from mindsets.
Examples of Recent Balloon Launches:
A balloon launch from Greece which used a very fast shutter speed to capture an image of the balloon bursting