ERMIS-3: Greek Nanosatellite Makes First Laser Link to Earth

Why use lasers

Radio frequencies are a scarce resource with limited capacity, while satellites keep multiplying and producing more data. Laser and radio signals both travel at the speed of light, but a laser can carry far more data at once, meaning greater bandwidth.

For ERMIS-3 this matters because of its hyperspectral camera, which splits light into many colour bands to monitor, for example, the condition of crops. The ESA mentioned that use when the satellite launched in late March. The high-resolution images are very heavy and hard to send down by radio.

Hard to aim, sensitive to weather

Lasers come with drawbacks. The beam is very narrow and must hit a ground receiver precisely while the satellite moves at several kilometres per second. Both terminals must find and then track each other during the satellite's brief pass. A single cloud can cut the link, and atmospheric turbulence degrades the signal.

The ESA did not disclose a data rate for ERMIS-3. The Greek test was meant first of all to show that the satellite could aim at the ground station, find it and track it.

Other CubeSats have already reached much higher laser speeds. In June 2023, NASA's PTD-3, carrying the TBIRD laser payload, transmitted 4.8 terabytes of data in a single five-minute pass, at 200 gigabits per second.

The ERMIS-3 result therefore marks a pointing and tracking milestone for Greece rather than a speed record, and it lays groundwork for moving heavy Earth-observation imagery faster.