The final days of summer are here, why not do something outside while you still have the chance?

Launch a Raspberry Pi balloon!

As Neil Armstrong took a giant leap for mankind, he inspired one boy, watching at home, to send a bear into space.

As an adult, Dave Akerman launched Babbage on a high-altitude balloon with a camera, sending the teddy bear 39 km above the Earth. In a stunt that replicated Felix Baumgartner’s record-breaking skydive, Babbage was released for a free fall.

“At that height, there’s the slight curvature of the Earth, and the thin blue line of the atmosphere separating the ground below from the blackness of space above,” says Dave. “On a clear day, with a wide-angle lens, I’ve had the whole of southern England from Cornwall to Kent in the same shot.”

A high-altitude balloon (HAB) flight works like this: the balloon is filled with hydrogen so it rises at a speed of about 5 m/s. On the line between the payload and the balloon is a parachute, which is pulled closed during the ascent. After a typical flight of two to three hours, the balloon bursts at high altitude, and the payload drops. The parachute opens, and the payload returns to the ground. The payload includes a GPS tracker and a radio transmitter so you can follow its journey from the ground, and be ready to recover it. You can also receive images during the flight.

There are several options for the radio transmissions. Most people in the UK use RTTY (Radio Teletype) transmissions, but some also use LoRa, a proprietary long-range radio system that enables images to be downloaded more quickly. In some countries (but not the UK), APRS can be used, if you have an amateur radio licence.

“In the UK we have a widespread network of other hobbyists who will help during the flight, meaning that even if the chase car loses signal (e.g. it’s in a tunnel or on the wrong side of a hill) then the rest of the receiver network will fill in the gaps,” says Dave. Data from flights is fed into a distributed mapping system called Habhub. “With a well-tested radio tracker, the chance of not knowing where the payload has landed is pretty close to zero.”

Dave started out building his own tracking and transmission systems, but the Pi in the Sky (PITS) kit can now do this for you. Among other things, it enables data from the Sense HAT to be sent back during the flight.

“Some of my flights have had a 3G link at low altitudes (useful for streaming video to YouTube), or have predicted their own landing position during descent,” Dave says. “My current project is to use a gliding parachute or parafoil to land at a particular target location, using wind data measured during ascent to feed the guidance algorithm during descent.”

Dave advises new launchers to read as much as they can to avoid mistakes others have already made. “Read the UK High Altitude Society website, read various HAB blogs, and join the #highaltitude IRC channel on Freenode and introduce yourself,” he says. “Do all three!”

Three things you need to build a high-altitude balloon

Pi in the Sky kit

You can build your own tracking system, but the simplest option is to use the Pi in the Sky kit, which includes the GPS antenna and a radio transmitter.

Camera

Using a Raspberry Pi with the Camera Module, you can program the camera to shoot at certain altitudes only. Don’t use a case: it will trap moisture and ruin your images.

Balloon

The balloon carries your payload. Use the online calculator to work out which size you need: typically 800 g or 1000 g, depending on the weight of your payload.

Get permission

Before flying your balloon in the UK, you need to request permission from the Civil Aviation Authority at least 28 days in advance. Avoid areas near airports and air shows, and send an email to confirm (or cancel) your plans a few days before launch. Outside the UK, try asking for advice on the #highaltitude IRC channel on Freenode.

Don’t launch without permission: you might endanger aircraft!