Using an inter-satellite optical communication system, dubbed LUCAS, the pair were able to transmit data between ALOS-4 in low Earth orbit and the Optical Data Relay Satellite in geostationary orbit at speeds of 1.8 Gbps across 40,000km.
By using LUCAS, JAXA and NEC were able to significantly reduce the time it took to transmit Earth observation imagery covering areas such as the Arctic, Europe, and Africa in just 30 minutes — a process that would traditionally require multiple transmissions when sent directly to ground stations.
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The pair leveraged laser light, operating in the 1.5 μm optical wavelength band, to relay the data. The use of laser light allowed the satellites to transmit significantly more information compared to traditional radio wave-based systems.
The LUCAS system required precise optical systems to maintain a focused laser connection between satellites which were moving at high speeds.
Laser light uses highly focused beams with minimal risk of interference, enabling JAXA and NEC to achieve high-speed transmissions between the two satellites at rates 7.5 times faster than the 240 Mbps achieved by the space agency’s now-defunct KODAMA satellite, which relied on radio waves.
“The success of this data transmission utilising LUCAS enables immediate downlinking of a large amount of observation data, which is difficult to achieve through direct communication to ground stations in areas lacking accessible ground stations,” the pair said in a press release.
JAXA and NEC have been working together on optical communications since the 1990s, with the pair planning to further develop optical inter-satellite communication beyond the initial LUCAS tests to “contribute to the advancement of Japan's space”.
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