Written by Blake Raab (N4BWR)
On July 13, 2019, the West Georgia Amateur Radio Society launched a high altitude weather balloon from the VFW Fairgrounds in Carrollton, GA.
This was a 1200 gram weather balloon, and we used helium. The payload, which weighed 2.5 pounds, consisted of a crossband repeater and an APRS tracker, both custom designed and built by WX4BK. It also included two cameras. They were a Lightdow LD4000 that would point up at the balloon to catch burst on video, and a GeeKam that would point out the side to catch video of the flight.
Flight and Performance
We arrived at 9 AM and began preparations shortly thereafter. Balloon inflation was very easy and quick, thanks to the trusty inflation kit consisting of a hose with a CGA-580 brass fitting on one end, and a plastic piece on the other that fits nicely into the neck of the balloon. I'm still going to need to find a reliable and accurate way to measure neck lift. I needed an amount just under the maximum for the lift scale I was using, and the breezes made it difficult to judge that by providing artificial lift. We ended up with an ascent rate that reached just over 1000 feet per minute at times, which actually worked out well.
We had planned to connect the cameras to external power through the charging port so they could last the whole flight. The camera pointing up turned out to have a bad connection on the charging port, but somehow managed to survive long enough to catch burst and 20 minutes of freefall. I'm still not sure how that happened. The other camera, which did get to be connected to external power, covered the whole flight (and an hour of watching ants and bugs crawl on the leaves and branches that we landed on).
Leading up to launch, we had several minutes of panic, because nobody, even those on-site with equipment, was picking up any APRS telemetry from our payload. We reset the system and it started working. After that, the APRS unit worked flawlessly in flight. WX4BK was able to receive data from his home IGate from right after launch to near landing, while the payload was only transmitting at half a watt. Upon launch, we discovered that the crossband repeater seemed to have a faulty VHF module, so it was quickly decided to stop trying to use it to conserve battery for the cameras.
The balloon burst at 109,872 feet (which we caught on video) and descended rapidly. In the high altitude environment, there is almost no air, and therefore, very little aerodynamic drag to deploy the parachute. Because of this, the payload can tumble and spin wildly, all the way down to 50,000 feet. We had already lost a payload two years ago when it is believed that the antenna ripped off during this tumbling and spinning. We had another moment of panic on this flight when we lost telemetry for three minutes. We believe that the rapid spinning made the GPS briefly lose satellite lock.
Because I had slightly overfilled the balloon, we ascended more quickly, resulting in a lower burst altitude and a shorter flight distance than predicted (Play with the numbers in the CUSF Landing Site Predictor to see how those factors change things). We descended toward rural Alabama and an area where the only roads are county roads. That turned out to be quite an experience.
Some people seem to think that we failed somehow or that we encountered something unexpected when the payload stopped being received by IGates. In fact, this did not even happen until it was around 3000 feet above sea level, which was 1500 feet or less above ground level. This is to be expected. It was only transmitting on half a watt through a wire hanging below the payload. Once we got below the trees, it was not going to be received. This is why we run flight predictions and go to the anticipated landing site. Once we were near the last beacon point, we were within 1000 feet of the payload and could pick up the signal directly. The shape of the flight path stayed the same as the prediction. The only adjustment was to the ascent leg, since we had a higher ascent rate. Here is the predicted flight path compared to the actual flight path. The speed upon landing was within four feet per minute of what I wanted it to be.
Overall, it was a completely successful flight. There were lessons learned, and getting the full flight video and telemetry data certainly helped with that.