Success: Optical inter-satellite communication between the Optical Inter-Satellite Communication System (LUCAS) and the advanced radar satellite "DAICHI-4" (ALOS-4) claiming the world's fastest communication speed of 1.8 Gbps

October 8, 2024

The Japan Aerospace Exploration Agency (JAXA) has announced that the Optical Inter-Satellite Communication System (LUCAS)*1 onboard the Optical Data Relay Satellite*2 and the advanced radar satellite DAICHI-4 (ALOS-4)*3 will have a communication speed of 1.8 Gbps. *4 Optical inter-satellite communication has been successful.

Since July 4, JAXA has been conducting initial functional verification operations of DAICHI-4 (checking the operation of various onboard devices in orbit). As part of this work, we started testing DAICHI-4 against LUCAS on August 20. We established mutual acquisition and tracking between the optical inter-satellite communication equipment of DAICHI-4, which is about 40,000 km away, and LUCAS, an optical data relay satellite, and succeeded in transmitting commands to DAICHI-4 and acquiring telemetry from DAICHI-4. As a result, we confirmed that the data transmitted from DAICHI-4 reached LUCAS at the world's fastest communication speed of 1.8 Gbps (communication optical wavelength 1.5 μm band).

This is the world's first successful optical inter-satellite communication (geostationary orbit-low Earth orbit) at a communication speed of 1.8 Gbps in the 1.5 μm wavelength band. This is 7.5 times faster than the 240 Mbps transmission speed of the previous generation of the data relay technology satellite "Kodama" (DRTS)*5. This wavelength band is a general-purpose wavelength used in optical fiber communication networks on the ground, and it is expected to be used in space in the future because of its high performance.

With the successful communication between the low-Earth orbit satellite and LUCAS, it is expected that the communication time will increase.

For example, in the case of communication between a general low-orbit satellite and a ground station, the communication time is about 1 hour per day, but by relaying a geostationary orbit satellite with LUCAS, the communication time is increased to about 9 hours.

As a result, data acquired in areas where Earth observation satellites orbiting in low Earth orbit cannot communicate directly with ground stations can be transmitted to the ground in real time via geostationary orbit satellites. Similarly, in the event of an emergency, LUCAS can be expected to relay geostationary orbit satellites and send commands from the ground to satellites to quickly acquire images.

We will continue demonstration experiments using LUCAS and DAICHI-4 to evaluate how differences in the distance between satellites and their positional relationships affect communication quality, with the aim of putting them into practical use.