Double Pack Qualatex Floating at 9200 m

DL7AD-12 is the callsign of our (Sven and myself) next long duration mission attempt. The two 91 cm standard foil balloons were carefully balanced for a predicted lift of 3g at the 12.5 g heavy, solar powered tracker with LiFePO AAA size battery. After attaching the two ballons together with 6 strips of Tesa (Made in Germany Scotch tape) we had approximately 2 g lift. The advantage of this assembly is that the balloons don’t scratch on each other and the tandem has a much higher ascent rate because one balloon is in the (vertical) slipstream of the other. We were planning for a higher altitude, but we didn’t expect 9200 m of day float. This is a good thing and a bad thing. Good because we are above most clouds and humidity is significantly lower (promising a more stable float). The bad thing is that we’re pretty close to the 10,000m cruise altitude of commercial airliners. I don’t think we’ll try this exact constellation again and we hope to drift soon into more remote areas. However this experiment shows that with 2 balloons you can reach stable float and at the same time increase the lifting capacity. Because our usual supplier of uBlox GPS receivers was out of stock, we bought some MAX7c modules on ebay from China. On the Pecan 6 PCB which was tested & working with MAX8, we were not able to switch off the GPS with the p channel MOSFET. Very strange… Only 3 hours later we have found that our (possibly counterfeit) cBlox modules have an internal 0 Ohms connection between VCC and VCC_IO (pins 7 and 8). Cutting the trace below pins 6 and 7 resolved the issue. Being worried that those modules were fake, we’ve tried to simulate high altitudes with Sven’s new HackRF and GPSSsim. However everything worked, so we decided to leave the module on the tracker for this launch.

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