A formation flying around a halo orbit is discussed in this paper. We aim to form a natural and closed formation flying around a halo orbit to reduce fuel consumption. A method to form a periodic orbit using a monodromy matrix derived by linearizing the equation of motion of spacecraft is proposed, where the complex eigenvalues of the monodromy matrix and their corresponding eigenvectors are used to form multiple orbiting formations. Using the proposed method, it is confirmed that the formation in which a chief moves around the halo orbit a certain number of times and a deputy returns to its same relative position can be constructed with almost zero velocity increment. We also discuss the design of formation trajectories when adding velocity increments. The validity of the proposed method is confirmed by numerical calculations.

Wake survey of vortices shed from two co-rotating vortex generators in boundary layer developed on a flat plate was performed in low-speed wind tunnel. The two vortex generators were arranged in lateral direction on the plate at 20 deg angle of attack and the spacing of the models was varied as the control parameter in order to assess the interference in the wake flow. Five-holes pitot tube was used to visualize the distributions of velocity vector, total pressure loss and vorticity in a measurement plane which was set at 10c downstream of the models, where $c$ was chord length of the vortex generator. Drag coefficient was also estimated by the wake measurement. It was shown that two vortices shed from the models existed respectively when the spacing was large. The strength of Vortex A was always superior to that of Vortex B. Where Vortex A was defined by the vortex that was located in the upwash region generated by the other vortex (i.e. Vortex B). Note the vortex B was located in the downwash region generated by the other vortex (Vortex A). As the spacing between those two vortices A and B was decreased, two vortices were gradually dissipated. However, dissipation was more significant on Vortex B. The two vortices subsequently merged into a single vortex.

This study proposes a new method for shape control of non-spinning solar sails, in which Shape Memory Alloy (SMA) wires are exploited. An SMA wire is one of soft actuators that contracts at temperatures above its design value. In the proposed framework, the whole shape of a solar sail membrane is deformed via the contraction of SMA wires distributed over the membrane. The deformation results in the change in solar radiation pressure (SRP) torque acting on the solar sail-craft, which is applicable to fuel-free attitude control. In this paper, we investigate the theory of shape control using SMA wires. It is shown that a membrane under shape control behaves similarly both in a ground experiment and in a finite element method (FEM) analysis, demonstrating the validity of numerical modeling. With this result, the performance of shape control for a large membrane in a space environment is simulated by another FEM analysis. Results demonstrate that the proposed method is capable of producing SRP torque at an effective level for attitude control.

Though our developed nano-satellite, HIROGARI released to orbit in March 2021 achieved the missions successfully until the end of 2021, the satellite encountered significant problems in the early operation stage. Because the satellite condition did not follow the expected behavior, the operation policy had to be decided with insufficient data. However, it was difficult to decide the operation policy rationally, since a nano-satellite has poor battery and communication margins. For the next nano-satellite development, this study constructed a resilient operation model for a nano-satellite using Systems-Theoretic Process Analysis (STPA) with lessons learned from operation experiences of HIROGARI. STPA is known as a new hazard analysis method that focuses on the interaction between a controller and the controlled object and that can be applied in conceptual design stage before detailed configurations are determined. The resilient operation model was constructed by considering the ground station as the controller and the satellite as the controlled target. Then, validity of adopting STPA to construct the operation model is discussed through comparing the unsafe control actions (UCA) and our lessons learned from operation of HIROGARI.

This paper describes behavior of the shock absorption of Mars lander using aluminum foams. According to Mars atmospheric chemical model, oxygen concentration is constant regardless of altitude; however, observation by Herschel Space Observatory suggested the oxygen is abundant near Mars surface. For continuous observation on Mars, landing is planned using simple and small lander. Therefore, we have proposed expandable landing system using aluminum foams with energy absorption capability. In order to protect the payload, it is important to study landing behavior of the proposed system. In this study, mathematical model is formulated for the landing system and the landing behavior is numerically analyzed. Furthermore, a method to optimize the parameters of the proposed landing system using aluminum foams and numerical analyses shows the validity of the proposed optimization method. In addition to above numerical analyses, experimental validation evaluates the landing performance of the proposed landing system and proposed optimization method is validated.

An electrostatic levitation furnace is used to simulate a small space debris heated to a high-temperature in space and to measure thrust-force generated by irradiating a laser beam remotely on the simulated space debris. In the electrical levitation furnace, the divergence of the electric field induces the recovery force proportional to the displacement of an electrically-levitated target on the horizontal plane. The force/displacement proportionality constant, so-called spring-constant is calibrated through an impact-hammer method, inducing an intrinsic oscillation of the target by applying an impulsive force. The external force applied on an electrically-levitated-target in a horizontal direction is estimated from the product of the proportionality constant and the displacement of the target. In the experiment, an electrically-levitated zirconium droplet is heated and ablated by irradiating a continuous-wave carbon dioxide laser beam, and the thrust-force generated on the laser spot is measured.

Membranes can be applied to deploy high-capacity, lightweight and large structures in space, such as solar sails, occulters, and sunshields. However, it is difficult to predict the shape of the membranes under low tension in orbit, mainly because gravity deflects the membrane on the ground experiments. We propose a ground-based experimental method to simulate the shape of the membrane in weightless conditions by placing the membrane in an aqueous solution. We developed a small experimental system and measured the shape of the curved membrane that floated in a sugar solution. The effectiveness of the experimental method was evaluated by comparing the experimental results with the results of geometrically nonlinear finite element analysis. In addition, these results were compared with the results of the suspended membrane without gravity compensation.

We present the design, fabrication, and demonstration of a two-dimensional MEMS (microelectromechanical systems) optical scanner for a compact laser radar for a spacecraft landing on a planet. Electrostatic force caused by the voltages applied to the comb-like micro electrodes is adopted as an operation principle that is inherently robust to the harsh environment in space. Optical scan angles of 10^º × 15^º is obtained with drive voltages of 150V.

Cryogenic fluids such as liquid hydrogen and liquid oxygen used as the rocket propellants easily evaporate and form the gas-liquid two-phase flow. The control of the two-phase flow is difficult due to the large fluctuation of the density. For high-precision control, it is necessary simultaneously to understand flow regimes which represent a gas-liquid distribution pattern. Therefore, in this paper, we developed a classifier that uses Bidirectional LSTM networks, which is part of a family of deep learning methods, with a measured value of a void fraction meter as input and gas-liquid flow rate conditions as output, in order to realize a flow regime classifier in the future. The classifier succeeded in classifying with more than 80% accuracy. In addition, in order to verify what features of the input data the classifier captures, a test data-set of which frequency was artificially changed was classified. As a result, it was confirmed that the classifier would use the frequency component of the input data as one of the basis for classification.

We developed a new system that resembles a data server in order to collect data in a user-friendly and efficient manner, and conducted a demonstration experiment aboard an sounding rocket. In a 200-second experiment, we collected sensor data and images via various communication methods (Ethernet, Wi-Fi, UART, SPI, I²C) and successfully sent about 12MB to the ground.