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We used the CUSF Landing Predictor extensively throughout the week before the launch to follow how the weather conditions developed. The predicted flight path we got on Monday (5 days before launch) was only slightly off from the final prediction on the launch day, which was indeed very impressive.

However, as we got closer to the launch day, the wind direction in the upper atmosphere (between altitudes of 10 and 20 kilometers) shifted slightly towards north, which could make the balloon land on an area with several large lakes. This was obviously something we would like to avoid, so that we could safely recover the balloon payload hardware.

We even considered using an alternate launch site some 20 kilometers south from Hämeenlinna, but eventually ended up with a plan to fill up the balloon with slightly more hydrogen. This would increase the balloon ascent rate from the original plan of 5 m/s to over 7 m/s so that the balloon would simply rise up and burst sooner and avoid the areas with lakes. Our plan to use a higher ascent rate worked perfectly and even the maximum altitude of 28.3 kilometers was higher than the estimate burst altitude of 27 kilometers!

While APRS on the 2-meter band (144.800 MHz) was the main method of tracking the balloon, we only had a 70cm APRS IGate / receiver. This is because we have a very good APRS repeater and IGate coverage in Southern Finland that basically eliminates the need to set up your own receivers. During balloon descent, the last balloon position reports that reached the aprs.fi service had an altitude of under 300 meters, which confirms the APRS coverage.

The APRS tracker on the 70cm band (432.500 MHz), based on a Vaisala RS41 radiosonde, had quite a lot of issues with inaccurate GPS position information in high altitudes of over 10 kilometers. We do not yet know the exact reason for this, although we suspect it could be a result of some configuration setting for the RS41 GPS chip. After all, the firmware we used in the radiosonde had never been tested in high altitudes. Alternatively, the RF transmissions from other trackers could have interfered with the radiosonde GPS receiver.

The LoRa tracker was our backup tracker that we could use in case both of the APRS trackers failed for some reason. The Embedded Radio Tracker software, running on a Raspberry Pi model A+, also handled recording of sensor data and taking of still photographs using the Raspberry Pi HQ camera.

The LoRa modulation performs particularly well in low signal strength scenarios, such as the low-power transmitter in the balloon payload. The map below indicates the RSSI reading for calculated successfully received LoRa packets. The receiver antenna was a simple Diamond AZ-510 dual-band VHF/UHF whip mounted on top of car roof with a magnetic mount.

The LoRa receiver was located at the launch site all the time until the balloon landed. Before losing reception, the last LoRa RSSI readings dropped well below -120 dBm when the payload was over 50 km away and its altitude was below 5 kilometers during landing.

The DVB-S1 live video reception at the launch site worked really well considering this was the first time ever we had used such transmitter on a flight. The video reception was intermittent at times when the payload was spinning and swinging more heavily because of wind, but we did get really smooth video playback during the launch and even from altitudes near 20 kilometers where the wind speed was quite low.

Michael OH2AUE, located in Padasjoki, Finland, has shared the following videos about DVB-S video reception.

Video content received directly from the balloon DVB-S transmitter:

Michael’s setup for receiving the DVB-S transmission: