APPLICABILITY OF FREE SPACE LASER COMMUNICATIONS FOR MICROSATELLITES IN DIRECT AND INTER-SATELLITE LINK SCENARIOS

摘要

In space communications,information is transmitted to distant locations; therefore, radio waves are usually used. However, in recent years, along with the development of optical and laser technologies that have evolved from optical fiber communications, we have entered an era where laser beams (light waves) are used for communication between different types of space systems. Radio waves and light waves are both electromagnetic waves. However, the main advantage of using light waves in outer space arises from the extremely high frequency of laser light and the compact, light-weight, high-speed, and high-capacity equipment associated with it. Recently, there has been much research in the field of microsatellites. However, microsatellites, which weigh only a few tens of kilograms, have limited onboard resources, and thus communication speeds have been limited to about 9.6 kbps using amateur radio. Laser communication devices can be miniaturized, and microsatellites appear to be an extremely promising field of use for such devices. Lasers effectively use frequency resources, have no legal regulations or cumbersome international frequency management, and thus are a promising tool for the future. However, turbulence in the atmosphere must be considered in optical link analysis when performing direct downlink from a satellite to the Earth. In this paper, the applicability of space laser communications to microsatellites is described. Link analyses are conducted for three communication links: low earth orbit (LEO)-to-LEO, LEO-to-geostationary earth orbit (GEO), and GEO-to-LEO scenarios. In optical links through the atmosphere, atmospheric turbulence is considered in the link budget analyses. The onboard resources are also considered and the achievable data rate is presented for each scenario.