A new stratospheric balloon was launched by our team earlier this month, collecting valuable data on the interference events happening on the Romanian territory and demonstrating how our GNSS equipment can withstand these stressfull conditions.
Following the weather forecast and the simulation of the balloon’s trajectory, we noticed that it would fly from east to west, with a landing only 30 km away from the launch point. Once the launch day was established, we asked ROMATSA to issue a NOTAM alert, thus ensuring that air traffic participants are provided all necessary information.
The main purpose of this flight was the recording of the radio spectrum in the GNSS bands (GPS, Galileo, Beidou, Glonass), to document jamming and spoofing activities that have been observed in the Black Sea area. This phenomenon frequently affects the weather balloons launched from Bucharest at altitudes above 11,000 meters, but also the planes and maritime vessels in the region. In this context, we equipped the balloon nacelle with two HAPPi HAT GNSS receivers (developed in-house), which recorded the relevant data every second. In addition, the balloon payload included three recovery systems:
1. A Vaisala RS-41 radiosonde reprogrammed with software developed by OM3BC, configured for APRS emissions in UHF (432.5 MHz), RTTY and CW (435.5 MHz).
2. A picoAPRS Lite tracker developed by DB1NTO specifically for the flight of stratospheric balloons, configured to broadcast APRS messages in VHF every 30 seconds.
3. StratoFinder, a tracker with GPS, SMS and LTE/4G, equipped with an independent power system.
The preparations for the launch were intense and focused on the day before the event, involving multiple tests, subsystem integration and battery sizing to meet the 1150g mass limit, as well as the power budget.
The challenges began just before the launch, raising from the coordination with the Boboc airfield, which requested us to advance the launch time. Later on, we encountered some difficulties due to the construction of the A7 motorway, that forced us to move the launch site by about 500 meters. There were also difficulties in starting the equipment from the ground station, but we managed to overcome this issue.
The launch went smoothly without major problems. Filling the balloon with helium, connecting the parachute and the launch were carried out according to plan. The APRS igates network functioned flawlessly, the picoAPRS tracker was constantly received, being connected to one of the HAPPi HAT GPS receivers and providing an unaffected positioning of the GPS jams. The Vaisala radiosonde also worked well, being affected by spoofing only for a short period of 15 minutes, during the descent.
The HAPPi HAT receivers on board the balloon nacella transmitted a maximum altitude of 33.972 meters, followed by the balloon burst and parachute descent. The entire flight took about 3 hours. In the next chart, you can see the altitude measured by one of the HAPPi HAT receivers (marked with the green line) and the altitude measured by the GNSS receiver in the Vaisala radiosonda (marked with orange symbols). Jamming in the L1 and L2 GNSS bands was detected throughout the flight.
The ublox GNSS system included in the Vaisala radiosondes has been spoofed for about 15 minutes during the descent, reporting a position in the Ayvazovskogo airport area of the Crimean peninsula. The spoofing effect can be observed in the graph, through the altitude outliers that show unreliable measurements. at the end of hour 6 UTC. The number of GPS satellites used by the HAPPi HAT receiver for positioning (represented in blue) had a decreasing trend as the balloon’s altitude increased. Thus, after reaching the altitude of 10,000 meters, the number of GPS satellites dropped below 6 and increased above this value only when the equipment fell below this altitude, after the balloon burst. During the spoofing episode, the number of satellites dropped several times to 0, causing the receiver’s position to be temporarily lost for a short time. However, despite the constant jamming and reduction in the number of satellites being tracked, the HAPPi HAT receiver continued to offer a positioning solution for almost the entire duration of the flight. The analysis of the collected data demonstrates the reliability and robustness of the receiver under intense jamming and spoofing conditions, confirming the usefulness of these tests.
We would like to thank all radio amateurs who maintain the APRS network, which is an essential support in tracking and recovering the balloon. We are are determined to repeat this experience, collecting more data for radio spectrum analysis and we invite all those interested to participate in the live reception of data transmitted by the balloon. The launch day will be announced in the amateur radio communities and you can find the technical data necessary for the flight tracking on www.roinspace.com/ham.
