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Laser light has a bandwidth that is orders of magnitude wider than that of radio waves (5 THz in the 1.5 μm wavelength band), allowing it to transmit more information than radio waves. In addition, by using highly focused beams, there is little risk of interference or eavesdropping. The use of laser light is essential for achieving high-speed, high-capacity communications in space in the future. In LUCAS, optical communication has been adopted in the data relay system onboard the geostationary satellite. By using optical communication between the Earth observation satellite and the geostationary satellite, LUCAS enables data transmission from the Earth observation satellite at "1.8 Gbps", that is a speed 7.5 times faster than the "240 Mbps" transmission rate of the Data Relay Test Satellite "KODAMA" (DRTS)(4) using previous generation radio waves. (Figure 3)
There is a distance of about 40,000 km between "DAICHI-4" in low orbit and the Optical Data Relay Satellite in geostationary orbit. The acquisition and communication of the counterpart satellite, which is moving at high speeds, requires precise optical systems and their control technology. Specifically, while the Optical Data Relay Satellite in geostationary orbit at an altitude of about 36,000 km moves at about 3.1 km/second and the Earth observation satellite in low orbit circles at about 7.6 km/second, it is essential to continuously direct the laser beam, which expands only about 500 m, accurately to the counterpart satellite even at a distance of 40,000 km. To achieve this, high-output optical amplification technology for the laser light and acquisition and tracking technology to direct the laser light towards the counterpart satellite are required.
In this project, NEC developed the overall system design of LUCAS and both the laser communication terminals for the Optical Data Relay Satellite and the Earth observation satellite, the key components of LUCAS(5). The use of the 1.5 μm band, which is the hallmark of LUCAS, was based on NEC's development achievements in terrestrial and underwater optical fiber communication systems and was also developed in anticipation of integration with this system in the future. Although the 1.5 μm band is relatively deficient in power efficiency, the recent success in long-distance high-speed transmission between the geostationary satellite and the low earth orbit satellite is expected to accelerate its utilization in space-based optical communication.
"DAICHI-4" also carries SPAISE3 (Space-based Automatic Identification System Experiment3)(6) developed by JAXA and NEC, which particularly observes vessels in crowded maritime areas. Also for the observation data of SPAISE3, the optical communication makes it possible to transmit a large amount of data in real time. Like this, high-speed data communication using LUCAS contributes to the utilization and promotion(7) of not only SAR data but also various data of other satellites, thereby playing a role as a social infrastructure that protects people's lives and safety.
JAXA and NEC have been engaging in optical communication in space since the 1990s. Optical communication in space is also identified as a technology of strategic importance in the Space Technology Strategy formulated by the Japanese government for fiscal year 2023. JAXA has advanced research and development in optical communication as a solution to the increasing capacity and immediacy requirements of data transmission for future Earth observation satellites. NEC has been responsible for designing the LUCAS system, manufacturing laser communication terminals, supporting satellite system tests, and managing the initial functional verification operations of satellite systems. Building on this success, we will continue to contribute to the advancement of
(1) LUCAS: Laser Utilizing Communication System, developed and being operated by JAXA, is a system that enables data relay between an Earth observation satellite (low orbit satellite) and an optical data relay satellite (geostationary satellite) through optical communication in space using invisible laser light with a wavelength of 1.5 micron. www.satnavi.jaxa.jp/ja/project/lucas/ (Japanese Only)
(2) Earth observation satellite developed and being operated by JAXA. This radar satellite expands the observation range up to four times while maintaining the high spatial resolution of its predecessor "DAICHI-2". www.satnavi.jaxa.jp/ja/project/alos-4/ (Japanese Only)
(3) JAXA Press Release on
(4) "KODAMA": Launched by the third H-IIA Launch Vehicle on
(5) NEC develops laser communications terminals for JAXA's Laser Utilizing Communication System, "LUCAS" www.nec.com/en/press/202012/global_20201210_04.html
(6) SPAISE3: SPace-based AIS Experiment 3. SPAISE is an abbreviation for the experiment (SPace-based AIS Experiment) where the Automatic Identification System (AIS) is mounted on a satellite. AIS is a mandatory for all passenger ships, as well as international voyage ships of 300 tons or more, and all vessels of 500 tons or more, in order to ensure navigational safety. www.satnavi.jaxa.jp/ja/spaise/index.html (Japanese Only)
(7) JAXA Space Technology Directorate I Satellite Navigator "Satellite Applications" https://earth.jaxa.jp/en/application/index.htmlShare
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