yasutaka satou

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.

Spin-type solar sails have the advantage of being lighter compared to other deployment methods, but can exhibit complex deployment dynamics. Severe asymmetric dynamics was observed in the deployment experiment in a vacuum chamber. In this study, this deployment behavior is reproduced by numerical simulations using multi-particle techniques that take into account membrane collisions. We propose a simple method to predict whether a significant asymmetry will occur by calculating the energy change of the membrane. The conditions for realizing symmetric deployment are presented.

Space membrane structures provide a large surface area while being lightweight and efficiently storable. Two types of deployment methods have already been demonstrated: using booms or centrifugal force. However, it is difficult to control the deployment force in high frequency, and the associated impact and vibration to the membrane structures pose risks for mission failure. This study proposes a new deployment method using electromagnetic force. This method flows electrical current on the membrane to deploy via electromagnetic force. While electromagnetic force can be manipulated by changing the electrical current, electromagnetic force is also affected by the membrane deployment behavior. Since electromagnetic force is weak, the influence of environmental forces on the deployment behavior becomes larger than in the previous methods. Thus, to achieve consistent electromagnetic force control, the deployment behavior should be understood. This study aims to reveal the possibility of deployment using the proposed method and investigate the deployment behavior in LEO with numerical simulation based on the multi-particle method. From the results, this research finds that the membrane deployment with the proposed method can be divided into three phases. Furthermore, this study reveals the relationship between the deployment behavior and electromagnetic and environmental forces in LEO.

<p>In this paper, the completion conditions for a latch mechanism with a kinematic coupling, which consists of three v-groove/sphere pairs (Maxwell type), are approximately derived as a relationship between the slope angle of v-grooves and friction coefficient. The kinematic coupling is an economical and suitable method for attaining high repeatability in fixtures. Therefore, the kinematic coupling is used in various types of deployable space structures, such as the James Webb Space Telescope and the extensible optical bench of ASTRO-H (Hitomi). In previous studies, numerical simulations were carried out to determine the amount of additional force that should be applied to complete the latch from the incomplete state. However, it is difficult to use such numerical solutions as general design criteria. In this paper, approximated completion conditions are described using analytic functions. As a result, the derived completion conditions are intuitively clear and usable as design guidelines. The most severe condition, where two v-groove/sphere pairs are latched and only one pair remains unlatched, is clarified. It is shown that there are an optimum slope angle and upper limit of the friction coefficient for latch completion. Finally, the most severe completion condition is verified through experiments.</p>

<p>This paper proposes a novel control technique for a new panel quasi-static deployment and retraction method using electromagnetic force. This panel system is modeled as a multibody dynamic system which will be used for numerical simulations. Although the electromagnetic deployment has various beneficial points, it still has a major technical issue that vibration on panels continues for a certain time, and hence its motion does not converge quickly. To eliminate or damp these vibrations, we propose both feed-forward and feedback control methods using magnetism generated by electronic current. These methods can successfully reduce convergence time of deployment motion by at most 60 percents. Additionally, to realize feedback control, it is required to estimate the state variables of panels, that is, the angle between the panels. For that purpose, we introduce a new approach to determine these angles by sensing electromagnetic field generated by the deployment system with a magnetometer. This new method accomplishes the determination of the angles between the panels to an accuracy of at worst four degrees and one degree on average.</p>

The balloon-borne VLBI (very long baseline interferometry) is a radio telescope for space observation from the stratosphere in the submillimeter wave band. The primary reflector has an aperture of 3 m in diameter whose degradation of aperture efficiency is required to be less than 17 % under the deformation due to variations of elevation angle and temperature during observation.In order to alleviate the deterioration of the aperture efficiency, the sub-reflector is equipped with a focal position adjustment mechanism. However, the adjustment mechanism may fail during observation, so that the focal position will be fixed at the prescribed position.This study evaluates the effect of the adjustment mechanism failure on the aperture efficiency through multiobjective optimization approach. The design problem has thirteen objective functions that correspond to the nominal observation condition and the other six conditions considering elevation angles and temperatures with normal and failure cases of the adjustment mechanism.The design problem is solved using the satisficing trade-off method (STOM). As STOM can obtain the single Pareto solution corresponding to the user's preference for each objective function by introducing an aspiration level, the trade-off analysis is easily performed.

Guided-pin mechanisms for large space membranes are developed for the purpose of folding a tapered pattern precisely and folding a larger membrane using a smaller apparatus. The guided-pin, which applies displacement to the fold line, is introduced to the fold apparatus. To realize folding with the guided-pin, guided-pin mechanisms are designed, where a mixed spiral fold is employed as the target fold pattern. The guided-pin mechanisms are manufactured to perform fold experiments using the guided-pin. The experimental results show that a 5,000 mm-sized membrane can be completely and precisely folded by 1,400 mm-sized guided-pin mechanisms, and thus, the feasibility of folding using the guided-pin mechanisms is verified.

This study estimates the effect of creases, or plastic wrinkle lines, on the out-of-plane stiffness of solar sails. A method to simulate the crease effects using reduced-order finite-element (FE) models is proposed, and is applied to a practical solar sail architecture. A detailed crease shape is determined by a geometrically nonlinear FE analysis using a simple model first; the effect of creases is then replaced by beam elements. This method substantially reduces the computational effort required for the FE analysis of a solar sail model. The result suggests the significant impact of creases on membranes out-of-plane stiffness when the tension level in the membrane is small.

This paper proposes a method to store a large solar-sail membrane while ensuring repeatability of its stored configuration. Large membranes used as a solar sail should be stored compactly to save the launch volume; in addition, their stored configuration should be sufficiently predictable in order to guarantee reliable deployment in orbit. However, it is difficult to store a large membrane compactly because of the finite thickness of the membrane. This paper demonstrates the feasibility of the proposed "bulging roll-up" method experimentally using 10m-size membranes, and evaluates the repeatability of its stored configuration quantitatively.

Piecewise Straight Fold is proposed for large solar sail membranes to simultaneously realize the high packaging efficiency and the simple folding. The fold pattern is based on Spiral Fold to reduce the deviation of the fold line, which improve the packaging efficiency. In addition, the fold pattern consists of piecewise straight fold lines, which approximate the Spiral Fold line, in order to simplify the folding. A simple manufacturing process of Piecewise Straight Fold is developed based on the Z-fold membrane. The preliminary experimental results show the feasibility of the Piecewise Straight Fold and its simple manufacturing process, where the high packaging efficiency is also verified. The wrapping fold experiments for the solar power sail membrane is demonstrated by using the Piecewise Straight Fold. In the wrapping fold experiments, the applicability of the Piecewise Straight Fold to the solar power sail membrane is verified.

This paper addresses the design of a rib-stiffened shell antenna with the adaptive structure system by simultaneous optimization of the structure and the actuators to improve the surface accuracy of the space antenna. A rib-stiffened shell antenna is proposed for the antenna structure concept with the adaptive structure system. The simultaneous design optimization is performed for the 1/6 element model of rib-stiffened shell antenna. The results of the design optimization show that the higher precision surface can be obtained by the simultaneous optimum design than the individual optimum design. The feasibility of the simultaneous optimum design is examined experimentally. The surface error obtained by the experiment is in agreement with the surface error of the design optimization, and thus, the feasibility of the simultaneous optimum design is verified.

This paper addresses a elasto-plastic behavior of creasing process for a z-fold membrane to examine the mechanical properties of the crease, which determine the folding and deployment characteristics of a large membrane. To examine the elasto-plastic behavior in terms of the layer pitch and the contact force for creasing the membrane, fold experiments are performed. The experimental results are evaluated numerically by demonstrating elasto-plastic FEM analyses, and examined theoretically by introducing a mathematical model. In the FEM analyses, the precision is improved by investigating numerical parameters; the penalty stiffness for the contact analyses, the numerical damping in the equilibrium equation, and the size of the finite element mesh, which are dominant parameters in non-linear FEM analyses. In the mathematical model, the mechanics of the creasing process is formulated for elastic deformation. These results indicate that the loading process of the creasing properties is confirmed in terms of the contact force and the layer pitch. On the other hand, the further examinations are requested for the unloading behavior to determine the mechanical properties of the crease precisely.

Folding FEM analyses are presented to examine folding properties of a two-dimensional deployable membrane for a precise deployment simulation. A fold model of the membrane is proposed by dividing the wrapping fold process into two regions which are the folded state and the transient process. The cross-section of the folded state is assumed to be a repeating structure, and analytical procedures of the repeating structure are constructed. To investigate the mechanical properties of the crease in detail, the bending stiffness is considered in the FEM analyses. As the results of the FEM analyses, the configuration of the membrane and the contact force by the adjacent membrane are obtained quantitatively for an arbitrary layer pitch. Possible occurrence of the plastic deformation is estimated using the Mises stress in the crease. The FEM results are compared with one-dimensional approximation analyses to evaluate these results.