This is our first launch with a Pecan Femto 3 tracker. With broken off pin header the weight of the complete PCB is 0.91 g (0.032 oz). However there is a big LiPo battery (11.5 g, 560 mAh) on board this time. The total payload weight including solar cells and mounting was 14.34 g. The balloon was custom made by Uta (1.40 m x 2 m). Total lift 12.3 g. Track DL7AD-12 in aprs.fi or at tracker.habhub.org .
During the night the temperature dropped below -52 degrees Celsius. Obviously the LiPo battery didn’t make it and first the GPS stopped and later the transmit ceased entirely. We were lucky enough that the balloon came back to life in the morning at rising temperatures. We were happy to observe a further ascent up to 14.5 km altitude. The balloon appears to have a tiny pinhole because it slowly descended and landed in the mine fields near Sarajevo (Bosnia Herzegovina). Do not recover this payload!
Sven (DL7AD) has designed another miniature tracker board and we have soldered two PCBs last week. We have still two minor hardware issues that could be patched and the software needs to be re-written due to the new micro-controller. Current state is that on one board the GPS is unresponsive and on the other board the transmitter is broken. However that’s enough to work on the software for now. We’ll solder up some more boards next week and hopefully we’ll get a full working tracker soon.
Sven was trying an experiment with a foil balloon where he used concentrated sodium hydroxide to wipe off the aluminum layer from a Qualatex 90cm balloon. The removal of the aluminum worked fine, but we couldn’t measure any weight loss. At least it was below 0.05g. Still we wanted to launch this balloon to see if there is any difference. At our typical night launch we have lost visibility of the transparent balloon already after 200 meters. Usually you can see the reflections of the metallic foil balloon even after a mile at a regular launch, but this time it disappeared after a minute already.
The flight path during the night was unexpectedly low. There must have been a cloud layer that pushed the balloon back down at ~2700 m altitude. Possibly there was some little rain involved. In the morning hours when the sun came and dried the balloon, it finally continued the ascent up to 6521 m. Then the signal was lost just before the Russian border.
We’ve used a tiny Pecan Femto tracker powered by an AA Lithium Ultimate Energizer battery. When the balloon was lost, it certainly had still enough power. Many APRS packets were lost which indicates that the transmission was certainly not optimal. We’re investigating about the reason, but this was the first Femto flight with APRS software (Femto was originally RTTY only). Despite the small tracker, the payload weight was still ~20g due to the heavy AA battery.
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.
Launch in the early morning hours at full moon wih special guest Stefan (DK3SB). We’re testing a new AFSK modulation technique where the (rectangular) output of the micro controller is directly sent to the Si4464 chip through a GPIO pin. A digital (“GFSK”) filter inside the Si4464 is shaping the audio more smoothly. It seems however that several igates still have trouble decoding this signal. Only two solar panels seem to work fine (no difference to 4 panels). Time stamp issue from last flight is definitely fixed. GPS high altitude mode was verified to work with a GPS simulator.
Track DL4MDW-11 through APRS.fi or HABHUB
An amazing little kid’s balloon has visited 3 continents already and shows up now and then on the tracker maps. Here is the path so far: Germany > Poland > Czech Republic > Slovakia > Hungary > Croatia > Bosnia and Herzegovina > Italy > Lybia (predicted, but unconfirmed) > Greece > Turkey > Georgia > Russia. At the moment we’re likely floating above Kazakhstan or Siberia, but we’re out of range of any APRS igates.
I’m so glad that the tracker decided to wake up again after a stressful night. For some reason the GPS decided to have bad reception, which drained the battery and that in turn made the GPS to receive even worse. So at around 1:30 am the tracker quit sending APRS packages. We thought this was it and the battery is killed. But to our surprise DL7AD-11 appeared back on the map after sunrise had recharged the battery. Interesting turbulence around the Strait of Messina.
Sven (DL7AD) hasimproved the LPC1114 version of the Pecan Pico 6 software. He implemented a Unix like UTC timestamp and cleaned up the GPS coordinate calculations. He has found (and fixed) a bug that arbiarily changed the transmit frequency of the tracker due to false coordinates and the resulting impacts on geofencing. However he introduced a new bug where the APRS timestamp is falsely created when the Unix time crosses UTC midnight.
We’ve launched a floater yesterday evening. The solar powered tracker works fine and transmits positions and telemetry. However the timestamp is corrupt, which causes APRS.fi to reject all position packets. This makes tracking difficult, but we’ve found a couple of workarounds, how DL7AD-11 can be tracked for now:
Telemetry via APRS.fi
Raw Packets on APRS.fi
Position on habhub tracker
Position on OpenAPRS.net (need to find DL7AD-11 manually)
Position & Track on FindU
Position & track on www.DB0ANF.de
Back in Berlin Sven was already waiting for me to continue with exessive ballon launch sessions. First I tried to get an update on the legal framework in this country. From a non-lawyer perspecive I thought that the Luftverkehrs-Ordnung was applicable.
§ 16a Besondere Benutzung des kontrollierten Luftraums
(1) Bei Inanspruchnahme des kontrollierten Luftraums ist von der zuständigen Flugverkehrskontrollstelle eine Flugverkehrskontrollfreigabe einzuholen für
4. Aufstiege von unbemannten Freiballonen (insbesondere Wetterballonen) mit einer Gesamtmasse von Ballonhülle und Ballast von mehr als 0,5 Kilogramm,
This means that unmanned balloons below 500 grams total weight do not require a NOTAM to the German flight control.
Also note that a few lines above they mention:
1. Fallschirmsprünge und den Abwurf von Gegenständen an Fallschirmen;
This means that for legal reasons you DON’T want to use a parachute, else you need to report this in an official NOTAM. The restriction to 500 grams is actually an interesting challenge and with today’s electronics it’s entirely possible to launch all kind of interesting payloads below this weight limit. In fact I’ve ordered a couple of 150 g balloons and we built our own “Pi in the Sky” with the help of Dave Akerman‘s great descriptions, experience and software. Instead of a MTX2 we used a modified Pecan 144.600 MHz transmitter at 1000 Hz shift at 600 Baud RTTY. At a total payload weight of 125 g and a 150 g latex balloon we were far below the 0.5 kg limit, but still we’ve got an impressive flight with ssdv pics up to an altitude of 23.5 km and of course: Landing in a tall tree…
Launch from St Arnolds brewery went smoothly with low winds and not much trouble. I simply adjusted the lift to ~1-2 g at home, put the complete balloon and tracker in my car and launched it at the brewery.
In the mean time we have reached float altitude at 25000 ft. I hope the battery will survive the night. Once we get some sun the battery will charge up fast. However if the battery dies, the tracker won’t start up by itself. The GPS draws too much current at start up. I have to add a transistor to actualy switch the GPS off until the battery charges up to an acceptable level.
But we’ll see. Maybe everything works out fine. Prediction says that the balloon will got to Mexico and come back over Texas to continue East when the jet stream picks up. Track KT5TK-11 on APRS.fi