ABSTRACT
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Space optical communications from small satellites need to be developed for the high-data-rate communications page link to the ground. The requirements for the onboard resources are discussed with respect to the antenna diameter, the mass, and the consumption power. The development for a small optical transponder has begun and the data rate will be on the order of several ten-Mbps. The mass of the small optical transponder will be about 5 kg, which can be embarked on 50-kg-class small satellites as the piggyback of launch vehicles.

a 50 kg-class satellites can reduce production cost and time compared to larger satellites. On the other hand, the communication capacity in radio frequency for 50 kg-class satellites is limited, however it can be improved by using optical communications. The National Institute of Information and Communications Technology (NICT) Japan has begun to develop a Small Optical TrAnsponder (SOTA) onboard a 50 kg-class satellite, which project is called the Space Optical Communications Research Advanced Technology Satellite (SOCRATES). We will introduce the SOTA onboard the 50 kg-class small satellite.