The Japan Aerospace Exploration Agency (JAXA) reported that it has conducted a series of successful experiments on organizing optical communications in near-Earth space. The data was transmitted from a satellite in low orbit to a relay satellite at an altitude of 40 thousand km. At the same time, a record transmission speed of 1.8 Gbit/s was achieved for the given conditions, which will be reflected in a new level of control of long-range Earth sensing satellites.
On the left is the optical communication module for the relay satellite, on the right is for Daichi 4. Image source: JAXA
The data was collected by the latest spy satellite Daichi 4 (ALOS-4). It was launched into geosynchronous orbit on July 1, 2024. Testing of its operation began on July 4, and testing of the space optical communications module began on August 20. Data via an optical channel was received by the experimental LUCAS satellite in a sun-synchronous orbit at an altitude of 40 thousand km. Then he broadcast them to Earth via a regular radio channel. The maximum achieved optical communication speed between satellites was 1.8 Gbit/s, which became a world record for the conditions created.
Japan will continue experiments with optical data transmission at other altitudes, for example, from the Kibo optical module to the ISS (for LEO 400 km). Optical communication with the transponder will allow Earth observation satellites like Daichi 4 to remain actually transmitting data to Earth longer. In particular, without a repeater, communication from Daichi 4 to a ground station lasts only 1 hour, while through LUCAS it is extended to 9 hours.
It is important to note that the transmission was carried out in the optical range of conventional fiber networks – 1.5 microns. JAXA believes that this is the most promising path for the development of space communications – in the range for which equipment is produced in the greatest volume.