Presently, the farthest CubeSats have gone into deep space was via a piggy-back ride to the orbit of planet Mars where a twin-6U CubeSats (MarCO-A & B) in formation provided X-band (8.425GHz) radio-frequency (RF) communication relay support between the Insight Lander spacecraft and the NASA Deep Space Network (DSN) receiving system on Earth at about 8Kbps data rate. Subsequent planned interplanetary CubeSat missions (such as the ESA Asteroid Impact and Deflection Assessment collaborative mission) seeks to leverage on and improve the capacity. The increasing demand for higher network bandwidth and system data-throughput has led to the utilization of higher frequency bands in the electromagnetic spectrum and increase in transmitter power for long range scenarios. Operating at higher frequencies (or shorter wavelengths) provides an expanded channel capacity and reduction in the transceiver components sizes comparable to the lower frequencies (VHF, UHF) counterparts. However, RF signals are highly susceptible to divergent spreading, atmospheric absorption and attenuation, severely limiting the communication system performance and efficiency. The RF spectrum is also fast becoming congested with severe signal interference problems especially in collocated and multi-node systems. On the contrary, the optical bands are currently underexplored, less regulated and without licensing complications. Free-space laser communication represents a paradigm shift in modern high-rate data link and information processing capability enhancement. Laser signals have very high directivity, significantly increasing the transmitter’s effective isotropic radiated power (EIRP) and improving the received signal to noise ratio in a long distance link such as direct deep-space satellite to ground communication system. Compactness of opto-electronic components is likewise attractive for very low-resource (size, weight and power) small satellite platforms, especially CubeSats. On the contrary, the suiting benefits of the narrow laser beamwidth simultaneously give rise to misalignment challenges, pointing and acquisition, tracking (PAT) problems, resulting to pointing errors between the communicating nodes. Platform disturbances and micro-vibrations from satellite onboard subsystems and deployable appendages also contribute to the laser signal pointing instability. A small satellite in deep space establishing an optical link with the ground will require a very strictly precise attitude determination and control system working together with a rapid response beam stabilization system having a high level of reliability and accuracy. Lean or small (commonly used interchangeably) satellite philosophy is gaining prominence in defining the current and future architecture of space exploration missions. In recognition of this, the International Academy of Astronautics constituted a Study Group to define the industry standards and requirements of small satellites. The lean satellite approach seeks cheaper, quick development and delivery of small satellite missions, utilizing commercial-off-the-shelf components, smaller human resource and faster mission turn-around time. CubeSats are getting more roles and are consistently been considered for demanding tasks which were once the domain of traditional satellites. However, there exists a number of technology gaps that must be filled before the full potentials of CubeSat applications for very high throughput missions and deep space exploration can be fully harnessed. Gigabytes rate communication transceivers, compact propulsion system, interplanetary guidance and navigation systems are a few of the current technological gaps. This research is focused on tackling the problems of laser communication adaptability on small satellites in considerable range with Earth-bound optical ground systems. To this end, the systematic design of an example theoretical mission described in this thesis adapts lean satellite initiative, use of COTS components and scalability. A new approach of utilizing Photodiode Array (PDA) as an optical feedback sensor applicable to a MEMS Fine Steering Mirror (FSM) based laser beam fine pointing and control system is introduced in this thesis. Analyses and experiments demonstrated that the PDA have a much improved frame rate, eliminating the feedback delay experienced in the use of CCD cameras for laser beam position control. This presents a useful improvement in the performance of optical beacon tracking and fine pointing systems for laser communication modules in small satellites. Experiments on characterization of platform jitter spectrum and beam steering system mitigating the jitter effects in a 6U CubeSat platform is also presented in this thesis. CubeSats and Unmanned Aerial Vehicles (UAV) are identical in terms of “leanness” or “scarcity” of onboard resources and are both considered as viable host platforms for laser communication devices in a ubiquitous optical communication regime. As a derivation of this research, the activities of the Japanese’ National Institute of Information and Communications Technology, NICT-Kyutech collaboration on the development of a Drone 40Gbps lasercom fine pointing system is discussed. The Drone lasercom project sought to advance the state-of-the-art in UAV communication capabilities, with the agile optical coarse tracking, acquisition and fine pointing system playing a very critical role. In conclusion, the work done and reported in this thesis contributes to the advancement of free-space laser communication technology on small satellites in both near-Earth and deep space scenarios.九州工業大学博士学位論文 学位記番号：工博甲第537号 学位授与年月日：令和3年12月27日1. Introduction |2. Background and Literature Review |3. Lunar Cubesat Lasercom Design Reference Mission |4. Photodiode Array Aided Laser Beam Steering Experiment |5. Cubesat Jitter Effects on Lasercom Beam Pointing Stability |6. Drone 40gbps Lasercom Project |7. Conclusion and Recommendations九州工業大学令和3年
