Optical technologies demonstrated and required towards the implementation of space optical communication systems between space and ground are described. The objective of this survey is to clarify the required technologies remained in backend segment for the future practice and to present a pathway to implementation by those expected to provide space optical communication services not only in the space development field, but also in the commercial field. We first overview optical communication systems for space-to-space and space-to-ground services respectively. Next, network segments, nodes and links are explained in expected networks. Additionally, technical tasks with lessons learned are revealed with demonstrated technologies, and then, technologies in front and backend segment required for network operations are presented together with remaining operation issues. Finally, the implementation of practical operations is presented based on our experiences with the ground segment development for space networks and low Earth orbit network systems.

The prevalence of serious incidents involving small, unmanned multirotors may escalate when such devices are operated within densely populated regions. The development of system fault detection techniques is required to prevent flight-related mishaps. A method utilizing an ultrasonic anemometer to detect damage to the rotor blade tip of a small multirotor has been introduced. This method can detect blade tip damage by analyzing the downwash speed, calculated by incorporating an extended Kalman filter. However, the efficiency of this approach in system fault detection remained ambiguous. To demonstrate the method's feasibility, a comprehensive investigation of rotor downwash was conducted. Employing smoke visualization, hot-wire velocimetry, and ultrasonic anemometry, the mechanics were thoroughly examined. Utilizing the experimental data derived from a quadrotor affixed to a test stand, a novel damage index value was postulated. This index value was then applied in a simulated scenario where one blade tip of a rotor was compromised during hovering flight. The simulation allowed for the detection of a 2-mm blade tip loss on a rotor with a 228.6 mm diameter. This study verified a technique for blade-tip damage detection predicated on sensing wake flow, thereby contributing to multirotor construction with robust failure tolerance mechanisms.

As the number of small satellites in low-Earth orbit increases, the goal of shortening the deorbit period after the end of operation has been set. Along with this trend, a more effective deorbit system than used to date is required. This paper proposes a deorbit component that combines a method of obtaining plasma drag by interference between on-orbit plasma and an electromagnetic field generated by an electromagnetic coil in a small satellite, and a method of obtaining air drag using deployable membranes. The proposed component uses a deployable membrane structure with electromagnetic coils, and it is possible to mount multiple components on a small satellite. It is possible to obtain greater drag using multiple components. In this paper, the plasma drag is calculated using the two-dimensional Full-Particle-In-Cell method when multiple deorbit components are mounted, and the appropriate coil arrangement is clarified. Furthermore, the deorbit duration is calculated by the total drag of the plasma drag and the air drag, and the performance of the proposed deorbit component is evaluated.

A nano-satellite called the re-entry satellite with a gossamer aeroshell and GPS/Iridium (EGG) was developed as part of the research and development of a re-entry system featuring a deployable membrane aeroshell. The EGG has a size of 3U (11 cm × 11 cm × 34 cm, 4 kg) including the packed membrane aeroshell. This membrane aeroshell consists of an inflatable ring and a membrane flare and can be deployed using a gas injection system installed in the EGG’s main body. The diameter of the deployed aeroshell is 80 cm. The EGG was deployed from the ISS by the JEM Small Satellite Orbital Deployer (J-SSOD) in January 2017. The aeroshell deployment sequence was successfully executed in February 2017. Images of the deployed aeroshell were captured by onboard cameras. After the deployment of the aeroshell, the EGG gradually lost altitude owing to the aerodynamic force acting on the aeroshell. This trend of orbital decay was confirmed by the GPS data. All flight data right until re-entry were acquired via the Iridium satellite network. Therefore, the EGG became the first satellite to rely solely on the Iridium satellite network for telemetry and command.

The revolution in the design philosophy of space systems has stimulated the growth of demand for replenishment, particularly in sustaining the continuous service of small satellite constellations. However, it is still unclear whether it is economically feasible to implement lifecycle replenishment and how it is affected by space system designs. To address the problems, this paper presents a quantitative methodology for analyzing and assessing the replenishment costs of space systems. Based on the formulations of the proposed space system characterization and lifecycle replenishment costs, the mathematical mapping relationship between space system designs and replenishment costs has been established. This connection enables the designers to explore and compare different system designs, regarding the major running cost of a space system. The results indicate that the cost of system replenishment can be effectively analyzed and assessed using the proposed methodology, helping to achieve a system design with a higher lifecycle value and to prevent problems such as cost overruns and schedule delays.