The last few months I have been providing engineering assistance to Wirral Grammar School for Girls in their project to launch a helium balloon into the stratosphere. This first chapter of the project was brought to a stunning conclusion yesterday when we successfully launched and recovered a camera payload, lifting it to a final altitude of 35.5 km (116500 ft).
Telemetry from the balloon was transmitted back to the ground using a pair of trackers made from a modified version of my sensor boards. The two trackers were configured on different bands using a 433 MHz and 868 MHz RFM22B module respectively, and custom firmware was written to communicate with a uBlox GPS receiver and transmit coordinates via 50 baud RTTY. The primary downlink was on 434.3 MHz and was received as far away as Belgium and The Netherlands (thanks to all who helped out).
The downlink was received and decoded in real time from a chase car, with a rough landing site being obtained before the signal was finally lost. Initial indications placed the landing worryingly close to a quarry, although a search with a 7 element yagi turned up an extremely weak signal which was enough to give us a bearing to follow – it turned out to be a further mile and a half away and behind a ridge, which is pretty good going for a 10 mW transmitter lying on the ground. A short drive further and another wave of the yagi yielded a GPS fix which turned out to be 50 yards into a field about a mile further down the same farm track. Recovery was quickly affected by DFing the 868 MHz tracker for the final few meters using the much more portable yagi we had for this band. The camera was still snapping, and had shot over 1300 images.
Many thanks to everyone on #highaltitude on Freenode IRC for their valuable advice, and especially to those involved in the provision of the tools at habhub.org and spacenear.us.
Update 25/10/2013: Some images from the flight are now available on the new gallery