KERAUNOS: a world-first in space-to-ground optical communications
A world first in optical satellite communications
In summer 2024, the KERAUNOS project achieved a major milestone in the field of optical space-to-ground communications.
For the first time, a stable high-speed optical communication link was established between a nanosatellite in Low Earth Orbit (LEO) and a commercial Optical Ground Station (OGS). During the experiment, the ground station successfully tracked the satellite, acquired the optical signal and maintained a closed-loop laser communication link for several minutes.
This achievement demonstrated that satellite-to-ground optical communications can move beyond laboratory environments and operate under real-world conditions. More importantly, it validated not only the performance of the optical terminal onboard the satellite, but also the operational capabilities of the Optical Ground Station itself.
For Cailabs, this milestone represented much more than a successful demonstration. It marked a key step in the transition of Optical Ground Stations from experimental systems to operational infrastructure capable of supporting future space networks.
The origins of KERAUNOS project
The rapid growth of Earth observation and space-based data services is creating unprecedented demand for high-capacity downlinks. While optical communication terminals onboard satellites have reached industrial maturity, the ground segment remains one of the major challenges preventing large-scale deployment. Building an Optical Ground Station capable of maintaining reliable communications through the atmosphere is significantly more challenging than deploying an optical terminal onboard a satellite. To address this challenge, the French Defence Innovation Agency (AID) selected Cailabs and Unseenlabs to collaborate on the KERAUNOS project.
The objective was clear: demonstrate a complete end-to-end optical communication chain between a nanosatellite in Low Earth Orbit and an Optical Ground Station representative of future operational deployments.
Building an end-to-end optical communication system
Establishing a reliable optical link between space and ground requires much more than integrating a laser terminal onboard a satellite. A ground station must continuously track a spacecraft travelling at more than 7 km/s, accurately acquire the optical signal, maintain the communication link throughout the satellite pass and compensate for atmospheric disturbances that can severely impact signal quality.
The KERAUNOS project was built on the complementary expertise of two French New Space companies:
- Unseenlabs, responsible for the space segment, integrating and operating the optical payload onboard its nanosatellite platform, and;
- Cailabs, responsible for the ground segment, including pointing, tracking, acquisition and optical reception capabilities.
For Cailabs, KERAUNOS was far more than a communication demonstration. The project enabled the validation of the operational building blocks required to establish resilient space-to-ground optical communications under real deployment conditions.
The campaign validated the successive operational steps required during a satellite pass:
1. Satellite acquisition
Using the satellite ephemeris, the dome opens automatically and the telescope points toward the horizon.
2. Coarse tracking
The OGS detects the flashes emitted by the optical communication terminal (OCT) and initiates coarse tracking. At the same time, uplink beacon laser signals are also pointing towards the satellite to allow the OCT to lock onto the ground-based optical station.
3. Fine tracking and communication link
The OCT locks onto the uplink beacon lasers and the OGS switches to fine tracking mode. The modem successfully detects the signal starting at 14° elevation.
From KERAUNOS to operational Optical Ground Stations
As part of the project, Cailabs designed, manufactured and operates its own Optical Ground Station from its headquarters in Rennes. Developed for operational deployment from day one, the station combines an 800 mm telescope with an architecture optimized for high data rates, low-elevation satellite passes and challenging atmospheric conditions.
Beyond the successful establishment of a space-to-ground optical link, KERAUNOS enabled Cailabs to validate the key operational building blocks of an Optical Ground Station under real deployment conditions. The project demonstrated the complete operational chain, from satellite acquisition and tracking to optical link establishment and communication through the atmosphere. The technologies, expertise and operational know-how developed throughout the project directly contributed of TILBA®-OGS, Cailabs’ turnkey Optical Ground Stations.
More than a world-first demonstration, KERAUNOS showed that optical ground stations can transition from research projects to reliable operational ground infrastructure supporting the next generation of optical space communication networks.