The day before the launch, we discovered a frequency clash with another payload being launched from EARS, and had to move the launch time from our planned 10:00BST to 8.30BST. After getting everyone out of bed at 5.30am we were at the launch site by 6:30 and final payload rigging, testing and setup were done. We had some electronics problems and it was not until 8:30BST we were ready to move out onto the field, and with filling taking a bit longer than expected we did not launch until approx 9.15BST. The weather was very windy and made filling quite a challenge. We went for neutral buoyancy at 4kg neck lift with a 1500g balloon so it was set to be a really quick ascent. The CUSF balloon calculator predicted a burst at 31-32km altitude.
We launched and suffered from this fast ascent in that temperature dropped very rapidly and caused serious frequency drift of the radio. The break in radio transmissions for approx 20s per minute was the uplink window, as the transceiver on the balloon was only half duplex. This combination of these two, and the fast that I’d forgotten to mention in my email that the payload was LSB, caused a lot of difficulty for people decoding across the country with the distributed listener system. On the plus side, the 300 baud transmissions worked extremely well and proved to be very decodable, even at altitude. Next time we will be re-thinking the transmission regime to increase decode-ability, and we will not use such a high ascent rate as this causes drift too severe for fldigi.
After launch, the minibus stayed at Churchill and tracked the payload with team members on the roof with a Yagi mounted on a camera tripod. Meanwhile, the chase cars drove to the predicted landing zone and continued tracking from there. The distributed listener system worked perfectly and Packet Handler retrieved information from it that we had missed whenever we had internet connection. We unfortunately made a mistake in the flight XML that we only recognised halfway through the flight, so the mapping part of the DL was not active for the whole flight.
At an altitude of just under 31km (30958m), at 10:41BST, the balloon burst and the payload began its descent. Initially everything seemed to be fine but at around 10km altitude the balloon probably tangled around the shroud lines and the payload headed to the ground at 10m/s. Luckily it landed in a cornfield and encountered a very soft landing.
We had frequency interference issues with another payload in the air, but luckily managed to receive a valid packet at 11:12BST at 339m altitude before we lost the balloon behind some trees. We quickly jumped in the cars and set of towards that location. As we got near, we heard the balloon with a whip, and eventually got close enough to decode another packet, and found its true landing location. It was in the middle of a large cornfield near the A11, with a small dirt track leading to the bottom end down which we managed to get the vehicles:
Once the payload was retrieved from its landing spot it was carefully disassembled for inspection. The soft landing meant the payload package had suffered very little damage apart from the antenna being bent out of shape, but this was soon rectified. We discovered that the camera pointing at the horizon had unfortunately been left in video mode and so CHDK had not been able to take any photographs. Happily, the other camera had been fine and had taken lots of pictures of the ascent. It had stopped photographing at around 21km altitude and the cause of this is as yet unknown.
We gathered a lot of very interesting information from the onboard sensors (raw data is here and graphs are here) and having recovered the payload, we were able to retrieve a full telemetry log from the onboard flash on the flight computer. The ionising radiation detectors were a broad success, although one did not work. The other cut out at 20.6km altitude and recovered on descending below 16km – the cause of which is again unknown. The landing prediction software proved extremely accurate and invaluable to the assessing the situation before deciding whether or not to launch. The final landing spot was within a few kilometres of the predicted one.
Overall we considered the flight a huge success. We successfully retrieved the payload which had broadcast faultlessly for the entire flight. We got some fantastic pictures, successfully flew and decoded the 300 baud transmissions, and we plan to carry out a lot of improvements and bug fixes, and then relaunch the payload in the near future.
We as a team would also like to thank everyone involved with this project for all their help, without which we would certainly not have been as successful as we were. Some notable people are listed below but this is by no means an exhaustive list:
- Ed Moore – for help and advice with the launch and filling, amongst other things.
- James Coxon – for his exceptional work on dl-fldigi and the special quick-switch baud version he released for our chase cars.
- Everyone who tracked the payload and submitted data to the distributed listener.
- Battery Force – for sponsorship in the form of the batteries that powered the payload successfully for the entire flight.
- Centronics – for generous provision of the Geiger-Müller tube ionising radiation detectors.
- Institute of Physics – for project funding to get Apex II off the ground (literally!).
- Dorking District Radio Society (DDRS) – for funding for the two Yagi antennas.