Figure 1 20-year evolution at NICT of transmission speeds and mass of onboard equipment for optical communication with low-earth orbit satellitesFigure 2 The CubeSOTA mission’s demonstration experiment plan: Direct communication with the ground (center) and CubeSat to ground communication via a data relay satellite (left and right)CubeSats, and optical communications are ex-pected to open up a whole world of new pos-sibilities for them.■NICT’s advantageous positionNICT has a long history of research and development in the eld of optical satellite communications. With regards to only low earth orbit (LEO) satellites, in 2006, NICT succeeded for the rst time in the world in demonstrating optical communications be-tween LEO and the ground at 50-Mbit/s using the Optical Inter-orbit Communications Engi-neering Test Satellite (OICETS), and less than 10 years later, NICT developed the world’s rst laser-communication terminal for micro-satellites called Small Optical TrAnsponder (SOTA), with 5-kg of mass. The SOCRATES satellite, equipped with SOTA, conducted a variety of experiments since 2014, such as 10-Mbit/s optical communication with the ground, and basic quantum-cryptography ex-periments. Currently, we are aiming to reduce mass and increase communication speeds with a LEO optical-communication terminal called CubeSOTA, designed for the CubeSat platform. As shown in Figure 1, it is expected that communication speeds will be increased by two to three orders of magnitude and that mass will be reduced by more than one order of magnitude.CubeSats can be put into orbit by launch-ing them on a rocket, or they can be released into space from the International Space Station (ISS). Japan is in an advantageous position because it has its own mechanism to release CubeSats from the ISS’s Japanese Experiment Module (JEM) using a robotic arm. The ad-vantages of using the ISS are frequent launch opportunities (approximately 6 times a year), that vibration can be reduced by a dedicated container, and that CubeSats can be checked in advance by an astronaut before their re-lease. The disadvantage though is that the ISS’s low orbit (approximately 400 km) lim-its the satellites to a lifespan of approximate-ly one year, which is sufcient for technical demonstrations.■Current research and development eorts at NICTBased on the experience miniaturizing SOTA, we are developing an even-more-com-pact communication terminal for CubeSats, which will demonstrate, in cooperation with the University of Tokyo, multi-gigabit com-munication using two CubeSOTA satellites (Figure 2). The rst one will carry out direct communication with the ground, and for the second one, we are considering a system that can perform intersatellite communication via a data relay satellite in GEO orbit.Challenges in development include min-iaturizing optical ampliers, telescopes, pre-cision tracking, and modems. As a rst step before launching the satellite for the purpose of demonstration and experiments, we are considering the use of high-altitude platform systems (HAPS), that can y as high as 20 km, well above the clouds just like satellites, but in a less-strict environment. We are also re-searching to develop portable ground stations that enable experiments in various locations at a low cost, and we are also conducting re-search and development on ground technol-ogies that can be easily deployed to support high-speed CubeSat communications at a more-affordable cost.At NICT, we are not only demonstrating the feasibility of high-speed communications for CubeSats, but also aiming to popularize it by miniaturizing optical-communication equipment, with the goal of developing an NICT prototype device based on a design that allows transfer of its technology to the pri-vate sector for future commercialization. It is hoped that enabling high-speed communica-tions for microsatellites will promote innova-tive scientic research and the development of completely new applications.11NICT NEWS 2021 No.1
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