Earlier this year, we reported on a ground-breaking experiment by the Université Grenoble Alpes, which planned to track three balloons at high altitudes to test the capabilities of LoRa® (Long-Range) and LR-FHSS (Long Range Frequency Hopping Spread Spectrum) wireless communication technology.
Working in collaboration with an ecosystem of commercial partners, including EchoStar Mobile, Semtech, The Things Network, and the LoRa Alliance® (see partner acknowledgements for full list), the Université Grenoble Alpes set goals to understand how LoRa® signal strength, network latency, and reliability are impacted at high altitudes and to identify optimal network configurations for enhancing IoT applications. Challenges include signal degradation and equipment endurance at significant altitudes.
Detailed data analysis and evaluations are still in progress. However, in this blog, we can share observations made during the experiment and the initial conclusions that can be drawn from it.
The balloons in flight
On 24th May, three specially designed balloons were inflated and launched from the CNES base at Aire-sur-l’Adour, France. As described in part 1 of this blog series, their gondolas carried the EchoStar Mobile EM2050 module, which utilises Semtech’s LR-FHSS (Long-Range Frequency Hopping Spread Spectrum) technology and connects to EchoStar Mobile’s LoRa®-enabled satellite network. They also carried a selection of IoT endpoints, antennas and ancillary equipment, such as battery packs.
Overall, the flights for the balloons went well. The flight duration of the first two balloons was between 1hr 30 and 2 hrs. The third balloon burst at a lower altitude than expected, which shortened its flight time. The balloons covered distances of 42, 41 and 58 kms respectively from the launching point, with all gondolas landing within a 10 km radius. The altitudes reached by the three balloons were 30,798m, 32,156 m and 26,627m. The minimum temperature recorded during the flight was -56°C.
Satellite signal and equipment performance observations
The EchoStar Mobile EM2050 module delivered reliable connectivity, robust signal performance and low latency throughout the balloon flights despite the high altitude and low temperatures. This performance was helped by the balloons having a clear line-of-sight to the satellite, travelling at an altitude high enough to be above the cloud line and any typical land obstacles. The other LoRaWAN® endpoints aboard the gondolas achieved transmissions up to 700 kms to LoRa® gateways operated by The Things Network (Spain and France), Requea (France), Orange (France) and Hélium (Spain and France). In addition, the satellite IoT tracking proved particularly useful for identifying the balloon gondolas’ landing positions in remote areas where terrestrial stations are hidden by surrounding hills or mountains.
Previous experiments, alongside this one, have shown that the external temperature does not vary at altitudes between 10 km to 18 km high, and is minimal (-45°C to -55°C depending on the season). During the slow ascent, both the insulation provided by the material used (2cm polystyrene panel) and the heat produced by onboard electronics/batteries allow to keep the internal temperature just a bit above 0°c). But, as the fall is fast during the first few minutes, internal temperature quickly drops, often down to -20°c, because of massive cold air entry. This can cause battery freezing, or temporary voltage drop.Despite these extreme temperatures, during this experiment, the camera and batteries continued to work, although the batteries’ power drained more quickly. This robust functionality allowed the camera to capture some outstanding images of the balloons and the stratosphere.
Conclusions
The observations and results of the high-altitude balloon tracking experiment are very promising for the application of satellite IoT in challenging environments. Despite the extreme temperatures and altitudes, the LoRa®-enabled satellite technology remained robust, maintaining resilient signal transmission and low latency over long distances. The experiment highlights that this communication can be relied upon for seamless data transmission no matter how harsh the conditions. It also emphasises the benefits of using LoRa®-enabled satellite networks to complement terrestrial networks for LoRa® applications, particularly when operating in remote areas.
As the Grenoble University Space Centre (CSUG) periodically launches sounding balloons for scientific and pedagogical purposes in order to teach STEM by practice, we can continue to learn more about communication technology, such as LoRa® and LR-FHSS, its integration with satellite networks and its wider application for a variety of use cases.
Partner acknowledgements
Thank you to our partners and collaborators for their support and expertise in making this high-altitude LoRa experiment possible:
Université Grenoble Alpes (CSUG, OSUG, LIG, LCIS, CROMA), INSA de Lyon CITI, IMT Atlantique, ANS Innovation, CNES Centre des Opérations Ballons de Aire-sur-l’Adour, REQUEA, Orange, Echostar Mobile, Kineis, Semtech, ChipSelect, Université Clermont Auvergne (LPC), Observatoire du Puy de Dôme.