yasutaka satou

This paper addresses the ways by which the releasing and deploying behaviors of a creased space membrane can be predicted accurately. Although existing studies have analyzed the released shape of a creased membrane by considering the elasto-plastic properties, the shape did not agree with the experimental results when the membrane was tightly creased. To examine the released shape of the membrane, creasing and releasing experiments are first conducted. The experimental results indicate that the opening angle of the crease increases with increasing elapsed time after the release due to stress relaxation. The stress relaxation behavior is predicted using finite element analysis (FEA) by considering the visco-elasto-plastic material properties. In addition, an analytical model of the releasing and deploying membrane has been proposed here. The results of the FEA and the analytical model indicate that the released angles are in good agreement with those in the experimental results. Thus, the effects of viscosity are considered important for predicting the releasing behavior of the space membrane.

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.

A novel approach for shape control of membrane structures is presented to realize their use in three-dimensional and variable configurations. The shape control is accomplished by exciting a spinning membrane. The membrane forms a shape consisting of several vibration modes, depending on the input frequency, and the wave surface stands still when its frequency is synchronized with the spin rate; that is, the wave propagation and the spin cancel each other, resulting in a static wave surface in the inertial frame. This idea enables control of continuous membrane structures with large deformation using fewer actuators than conventional methods. This paper describes the general theory of the static wave-based shape control. The mathematical model of membrane vibration, the classification of control input, and the control system for exciting a static wave are summarized. The proposed method is demonstrated through a ground experiment. A 1 m large polyimide film is rotated and vibrated in a vacuum chamber, and the output shape is measured using a real-time depth sensor. It is shown that the observed shapes agree with numerical simulation results. An additional simulation that models the Japanese solar sail Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS) demonstrates that the proposed method also works with a practically large-scalemembraneinthespaceenvironment.

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.

© 2020 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. In this paper, the deployed shape of spinning square solar sails was investigated through dynamic nonlinear finite element analysis of the full model of the solar power sail of the world’s first solar sail: Interplanetary Kite-craft Accelerated by Radiation of the Sun (IKAROS). The on-orbit photographs of IKAROS revealed that the sail membrane was deformed toward the sun and the membrane maintained its deployed shape during very low-spinrate operations. To clarify the mechanism of the deformation and high stiffness, the authors of the present study previously performed deployed shape analyses of one-quarter of one square sail by employing Abaqus and reported that the phenomenon was probably caused by curvatures of thin-film devices attached to the membrane. In this study, a finite element model of the entire square sail of IKAROS was created. Furthermore, deployed shape analysis under several combinations of curvatures and spin rates was conducted by employing the dynamic solver “Abaqus/ Explicit.” The results indicated that the sail deformations were induced by the curvatures of thin-film devices and that umbrella and saddle shapes appeared owing to the curvatures. The results also indicated that the electric harnesses between the sail and spacecraft supported the sail shape when the spin rate was low.

This paper presents a novel approach to sampling subsurface asteroidal regolith under severe time constraints. Sampling operations that must be completed within a few hours require techniques that can manage subsurface obstructions that may be encountered. The large uncertainties due to our lack of knowledge of regolith properties also make sampling difficult. To aid in managing these challenges, machine learning-based detection methods using tactile feedback can detect the presence of rocks deeper than the length of the probe, ensuring reliable sampling in unobstructed areas. In addition, given the variability of soil hardness and the short time available, a corer shooting mechanism has been developed that uses a special shape-memory alloy to collect regolith in about a minute. Experiments on subsurface obstacle detection and shooting-corer ejection tests were conducted to demonstrate the functionality of this approach.

© 2020 by the International Astronautical Federation (IAF). All rights reserved. A solar sail is not only propelled by solar radiation pressure (SRP), but also generates torque using SRP. When a sail membrane's shape is not flat, unexpected torque due to SRP is generated. It is necessary to control the sail membrane's shape and the resulting SRP torque to operate a solar sail for long periods and to reduce fuel consumption. Membrane shape control is a common issue not only in solar sails but also in space membrane structures. Therefore, we propose a method to actively control the in-plane and out-of-plane torque by deformation of the membrane shape using Shape Memory Alloy wires (SMA wires). An SMA wire is a type of a soft actuator that contracts when heated. In the proposed method, the SMA wires are attached at several locations on the sail membrane, allowing the entire membrane to deform in out-of-plane at the locations where the SMA wires contract. Furthermore, it is possible to control the membrane shape depending on the situation by selectively contracting subsets of SMA wires. In this paper, a finite element analysis and an experiment were conducted under the same condition to validate the numerical modeling for the SMA wire actuation. As a result, the validity of the membrane shape analysis could be shown since the tendency of the membrane shape deformation was the same in the experiment and the analysis. Next, the relationship between the SMA wire positions and the resulting SRP torque is clarified via another numerical analysis. Results show that in-plane and out-of-plane torques can be produced, respectively by contracting the SMA wires in line-symmetric and point-symmetric manners.

Transformable spacecraft under development is an innovative system that consists of several structural components, such as panels, connected together by internal force actuators. The spacecraft can change its structure drastically by driving installed actuators and achieve the following four features simultaneously. The first feature is "attitude change by internal force using non-holonomic characteristic of the system". It is possible to orient the spacecraft to an arbitrary direction by repeating the deployment of the panel in an appropriate order by the internal force actuator. The second feature is that "change of the structure enables the multiple functions by switching modes". Two telescopes will be installed for scientific missions utilizing the features of the transformable spacecraft and used to realize two different observation modes. One is a mode in which each telescope is oriented to different directions to perform wide-field observation (single telescope mode). The other is a mode in which two telescopes are pointed in the same direction. This mode enables the spacecraft to work as an interferometer (interferometer mode). The third feature is "orbit control and orbit keeping by controlling the solar radiation pressure on the spacecraft with the use of change of spacecraft structure". Since the spacecraft can change its structure by the internal force actuator, the orbit control and orbit keeping are achieved without fuel consumption. By utilizing this feature, the spacecraft will be injected into an artificial halo orbit around Sun-Earth Lagrangian point L2, and the technology demonstration of the transformable spacecraft and the observation mission will be performed in the orbit. The fourth feature is "passive cooling of observation equipment by use of panels as sunlight shield". In the observation mode, observation in the infrared region is performed and sufficient cooling is required. Appropriate arrangement of panels enables shielding of sunlight, and then the passive cooling of the observation equipment is realized. As a result, disturbance due to refrigerator is eliminated, which contributes to precise observation in addition to the contribution by non-holonomic attitude control without disturbance. This paper shows the analysis and experimental results for feasibility studies and conceptual designs of above four features. Furthermore, development status of the system and each subsystem to realize the spacecraft are introduced.

Martian Moons eXploration (MMX) is a mission to Martian moons under development in JAXA with international partners to be launched in 2024. This paper introduces the system definition and the latest status of MMX program. “How was water delivered to rocky planets and enabled the habitability of the solar system?” This is the key question to which MMX is going to answer in the context of our minor body exploration strategy preceded by Hayabusa and Hayabusa2. Solar system formation theories suggest that small bodies as comets and asteroids were delivery capsules of water, volatiles, organic compounds etc. from outside of the snow line to entitle the rocky planet region to be habitable. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. The mission is to survey two Martian moons, and return samples from one of them, Phobos. In view of the launch in 2024, the phase-A study was completed in February, 2020. The mission definition, mission scenario, system definition, critical technologies and programmatic framework are introduced int this paper.

© 2020 COSPAR This paper reports on the manufacturing and evaluation of a solar power sail membrane prototype for the OKEANOS project. The in-house prototype was built by the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. Mechanical and electrical evaluation tests were conducted. The membrane, thin-film solar cells, reflectivity control devices were good condition after the manufacturing and handling. The improvements in the manufacturing process and design were found. The manufacturing process and design were fundamentally established. After the prototype, improvement plans for the manufacturing process and design were tried. We have a prospect of manufacturing the flight model sail and continue to the development.

<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>

Solar power sail technique was demonstrated in the IKAROS mission. However, unexpected phenomena were confirmed. The membrane surface of IKAROS has deformed to a shape that was not flat. In the shape change of the film surface, it is known that the whole membrane surface changes greatly like an umbrella shape or a saddle shape depending on the warping direction of the thin film solar cell. Objection of this study is to clarify mechanism of influence on solar radiation pressure torque due to warp of membrane device and its solution method. Therefore, the shape of the overall membrane surface is clarified by using a simple FEM model and the SRP torque with respect to the shape is calculated, and the mechanism of the overall shape change in warpage and its influence is clarified. As a result, the influence on SRP is related to membrane surface stiffness and warped direction and it was found that it is best that the membrane is warped in the radial direction and its outermost stiffness is high.

In recent years, a large space film structure having a thickness of several micro and a shape of several to several tens of meters attracts attention, and various storing methods have been studied. Considering the thickness of the film surface at the time of winding before launching, there is a problem that circumferential difference occurs inside and outside of the folded film surface. In order to solve this problem, a method of solving the difference between the inner and outer circumference by predicting the inner / outer circumferential difference arising from the film surface and the thickness of the device and managing the phase has been proposed. On the other hand, the point that the target value for adjusting the phase is unknown and empirical was pointed out, and as a result of adjusting the phase, the wave-like slack that occurred caused the unevenness of the film thickness in the circumferential direction. In this research, we derive target value of phase management analytically, compare with experiment, and verify.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. In this study, we modify multi-particle method, a calculation method for predicting membrane behaviour, for evaluating collision between membranes and the change in membrane compression and bending stiffness due to devices mounted on membrane. This modification is verified its validity by the consistency with the results of the experiments conducted in the previous study. Then, we investigate the changes in the deployment behaviour when the temperature and thickness of solar cells change.

The balloon-borne very long baseline interferometry (VLBI) experiment is a technical feasibility study for performing radio interferometry in the stratosphere. The flight model has been developed. A balloon-borne VLBI station will be launched to establish interferometric fringes with ground-based VLBI stations distributed over the Japanese islands at an observing frequency of approximately 20 GHz as the first step. This paper describes the system design and development of a series of observing instruments and bus systems. In addition to the advantages of avoiding the atmospheric effects of absorption and fluctuation in high frequency radio observation, the mobility of a station can improve the sampling coverage ("uv-coverage") by increasing the number of baselines by the number of ground-based counterparts for each observation day. This benefit cannot be obtained with conventional arrays that solely comprise ground-based stations. The balloon-borne VLBI can contribute to a future progress of research fields such as black holes by direct imaging. (C) 2018 Published by Elsevier Ltd on behalf of COSPAR.

<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.

The combination of large membranes and light-weight deployable booms, often called a gossamer structure, has enabled innovative space missions, such as solar sailing, to become possible. Though many designs have been proposed and demonstrated, two problems remain regarding the folding patterns of the membranes. The first problem involves considering the thickness of a membrane to enable uniform and compact folding. The other involves membrane-folding patterns that allow for connecting the membrane to the booms at multiple points and deploying them together while minimizing the use of complex mechanisms. This study proposes three methods that consider the thickness, and two of them can keep the crease lines straight, in contrast to the conventional non-straight crease line solutions. In addition, this study derives one effective design to integrate a membrane with diagonal booms through the systematic classification of existing membrane folding patterns. (C) 2013 IAA. Published by Elsevier Ltd. All rights reserved.

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 the mechanics of a local buckling induced by wrapping fold of a membrane to identify the conditions for the local buckling, which determine the packaging density and the plastic deformation on the surface of space membranes. The packaging density is evaluated by investigating the configuration of the cross-section around the local buckling, which is obtained by finite element simulations. Based on the mechanical properties of the local buckling obtained by the finite element simulations, a simple analytical model is formulated to identify the dominant parameters and the conditions for the local buckling. As the plastic deformation is induced on the local buckling in the finite element simulations, the yield condition of the membrane material is considered in the theoretical analysis. These results are verified by performing the wrapping fold experiments. Based on these results, the mechanics of the local buckling is discussed. The dominant parameters of the local buckling are obtained by the theoretical analysis in terms of the tensile force, the membrane thickness, and the radius of the center hub. Also, it is found that the local buckling increases the layer thickness about 1.4 times when the radius of the center hub, the membrane thickness, and the tensile force are 75mm, 50μm, and 0.027N/mm, respectively. The conditions for the local buckling, where the plastic deformation on the local buckling is considered, are identified as the function of the dominant parameters, and the conditions are in good agreement with the experimental results. © 2012 by Yasutaka Satou and Hiroshi Furuya.

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.