森 治

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.

© 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This paper addresses how to design bonding area of the thin-film solar cell attached large space membrane structure. The solar cell glued membrane is easily deformed by the temperature change because of the thermal expansion mismatch between the solar cell the adhesive layer which decreases the power generation efficiency of the solar cell. On the other hand enough bonding area is required to have enough strength under deployment load condition. Thus an optimum bonding area design is examined by using FEA for a single unit of solar cell for OKEANOS membrane. The results of the analyses indicate that the above requirements can be satisfied by employing discreetly located bonding area with having curvature directionality. The obtained design is applied to the OKEANOS membrane where the deformed shape of the membrane with curved solar cell is obtained by FEA. As the results the membrane shape satisfies the requirements thus the effectiveness of the bonding area design is indicated.

© 2018 Univelt Inc. All rights reserved. Attitude dynamics and control of spinning solar sails are investigated considering the flexibility of sail membranes. Attitude maneuver of solar sails is, in many cases, performed using thrusters. In most studies, the attitude motion is analyzed assuming that the spacecraft is a rigid disk. However, the sail membrane deforms during attitude maneuver due to flexibility. This may cause coupled vibration between the spacecraft main body and sail membrane. This study presents an analysis model of spinning solar sail attitude dynamics considering sail deformation, based on modal analysis.

© 2018 Univelt Inc. All rights reserved. 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.

© 2018 Univelt Inc. All rights reserved. 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.

© 2018 Univelt Inc. All rights reserved. It is generally known that attitude of spacecraft having angular momentum on the spin axis moves like a vortex due to the influence of solar radiation pressure. Taking advantage of this motion, this paper proposes attitude control methods using biased (pseudo) equilibrium point. Slight change of the equilibrium point leads to stabilization of the motion. As the merit, only constant input achieves this proposed method. The purpose of this study is to verify the usefulness of the control method by performing numerical analysis on the stability of attitude motion.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. As fuel-free attitude control devices for spacecraft, we introduce Liquid Crystal Devices (LCDs). LCDs consist of multiple thin layers (∼ 150 µm thick in total) including Polymer Dispersed Liquid Crystal (PDLC) and a base film that has microstructure with aluminum deposited on it. By applying voltage, reflectivity of the surface of LCDs changes as the PDLC is directed to the electric field, and applying Solar Radiation Pressure (SRP) changes accordingly. In addition, the microstructure changes the angle of reflection only when voltage is applied such that incident light is reflected on the aluminum on it. These mean that LCDs can control both the magnitude and direction of reflection electrically, and three-degree-of-freedom attitude control can be realized by multiple LCDs mounted on a single plane controlling SRP. As light is diffracted on the microstructure and optical interference occurs, and PDLC has polarization effect, reflection on LCDs is a complex phenomenon and it must be understood for the design to realize desired performance. In this paper, we introduce basic reflection principles and a manufacturing method, and confirm them by making prototypes and measuring the distribution of luminous intensity. The performance of prototypes of LCDs is estimated based on the measurement. The results indicate validity of the reflection principles and the usefulness of LCDs considering the future view as attitude control devices.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Performance of solar sails largely depends on their attitude motion. Thrust vector of a solar sail is determined by its relative attitude to the Sun. Meanwhile, there exist some requirements on its attitude, for example, to secure enough solar power and ground communication. Therefore, conventional solar sail missions have strong constraints on attitude motion. This is because conventional solar sails assume flat sail membranes to avoid some unexpected deformation. This assumption leads to the fact that the geometry of the spacecraft is limited within two dimensions. This paper introduces a mission design scheme for spinning solar sails by actively controlling the shape of the sail membranes. The active shape control extends solar sails to three-dimensional structures, and hence the two-dimensional constraints can be removed.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. A spinning solar sail membrane with 14 meters in width and 7.5 microns in thickness of small solar power sail demonstration spacecraft “IKAROS” was deployed in space in 2010. After the deployment, images of the membrane taken by separation cameras and onboard cameras revealed that the sail membrane might be deformed toward the sun against the solar radiation pressure and that the membrane kept its deployed shape even under very low spin rate. In order to investigate the mechanism of the phenomena, the authors have performed detailed numerical investigations of the structure characteristics of the deployed sail employing the nonlinear finite element analysis software Abaqus. In the previous paper, it was reported that the curvatures of thin film solar cells attached to the sail might increase the stiffness of the membrane by conducting a static implicit analysis of Abaqus.1 In this paper, a new finite element model of the sail membrane is created and dynamic explicit analysis of Abaqus is employed to decrease the calculation time. Deployed shape analyses under several combinations of the curvatures and spin rates are conducted and the results which indicate upward deformation and high stiffness are obtained. Finally, geometric mechanism of the deployed shapes of the spinning square sail is discussed.

第48回月・惑星シンポジウム (2015年7月29-31日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県 48th ISAS Lunar and Planetary Symposium (July 29-31, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 14名ほか 資料番号: SA6000045020

木星のラグランジュ点付近に存在するトロヤ群小惑星の起源は、よくわかっていない。我々は（１）種々の氷・含水鉱物・有機物が特徴的な吸収を持つ赤外域（とくに2500$\sim$5000 nmの波長域）でトロヤ群小惑星のイメージング分光を行う母機（２）小惑星表面に降り立ち揮発性の高い炭素・水素・窒素・酸素などの同位体比をその場測定する子機、から成るソーラー電力セイル探査機の検討をすすめている。2020年代に打ち上げるために進行中の、ミッション設計・探査候補天体のサーベイ・搭載機器開発について報告する。

© 2015, American Institute of Aeronautics and Astronautics Inc. All rights reserved. This paper discusses the deformation properties of the solar sail IKAROS membrane to identify the possible causes of the phenomena observed by the flight data: the direction of the out-of-plane deformation. The flight data indicated that the direction of the out-of-plane deformation of the sail membrane was toward the Sun, although the solar pressure was applied from the Sun. This study hypothesized that the possible causes of the phenomenon is due to the initial curvature of the thin film devices on the sail and due to the circumferential slack induced by the bridges which connects each trapezoidal petal. The hypothesis was verified through geometrically nonlinear finite element analyses. The analysis results indicated that the sail membrane could deform in the Sun’s direction when the initial curvature of the thin film devices and the circumferential slack were simultaneously applied.

This paper gives a detailed evaluation of the solar and thermal radiation accelerations acting on the IKAROS solar sail and its spacecraft body during its operational mission from June to December 2010. In particular, the predicted temperatures are compared with actual in-flight measurements on the sail membrane as well as on the body. The results show fairly good correspondences in most cases but a few appreciable deviations have also been observed. The simulation results indicate that the magnitude of the thermal radiation perturbations on the solar sail trajectory is only about one percent of the solar radiation and may be neglected in view of the considerable uncertainties in the solar radiation force.

木星以遠の惑星探査においては,従来原子力エネルギーが用いられてきた.しかし,我が国の惑星探査においては,原子力利用は困難である.一方, JAXAでは光子を用いる推進と電気推進を組み合わせたソーラー電力セイルの研究が進められており,薄膜太陽電池を用い,従来にない軽量で柔軟性を有する大規模発電システムの研究開発を行っている.本稿では,形状制御,コーティングを行った薄膜太陽電池の評価試験,耐宇宙環境性,融着技術の検討による大面積薄膜発電システムに関して報告する.

This paper addresses the deformation properties of the IKAROS membrane to identify the IKAROS' higher out-of-plane stiffness, which was higher than expected. IKAROS' flight data showed that the out-of-plane deformation of the membrane was smaller than that predicted preflight by numerical simulations. A possible cause is the initial deformation of the IKAROS membrane, which is induced by the initial curvature of the thin film solar cells and the reflection control devices. In order to examine the effects of the initial deformation on the out-of-plane stiffness, nonlinear finite element analyses were carried out with shell elements for the 1/4 IKAROS membrane using the initial curvatures of the thin-film components. The results of the numerical simulations indicated that the on-orbit IKAROS membrane was nonflat due to the initial curvature of the thin-film components. The out-of-plane deformation with the initial deformation was found to be smaller than the deformation of the ideal flat membrane, and the numerical results qualitatively agreed with the IKAROS' flight data. As the initially deformed membrane increases the out-of-plane stiffness, which determines the deformation properties of the membrane, the bending stiffness is significant for the simulation of nonflat membrane structures. Based on the results, the mechanics of the higher out-of-plane stiffness of the IKAROS membrane was identified: it is the effects of the initial deformation of the membrane, which is globally propagated by the local deformation of initial curvatures of the thin film components.

ソーラー電力セイルは,ソーラーセイルの一部を薄膜太陽電池とすることで,光子加速と同時に太陽光発電も行う日本独自のアイデアであり,IKAROSにより世界で初めてこれを実証した.薄膜太陽電池の電力を用いて高比推力のイオンエンジンを駆動すれば,ソーラーセイルと合わせたハイブリッド推進となり,このコンセプトを踏まえることで,外惑星領域探査が可能となる.本論文では,IKAROSのミッションを紹介し,ソーラー電力セイルによるトロヤ群小惑星探査を提案する.

ソーラー電力セイルは,ソーラーセイルの一部を薄膜太陽電池とすることで,光子加速と同時に太陽光発電も行う日本独自のアイデアであり,IKAROSにより世界で初めてこれを実証した.薄膜太陽電池の電力を用いて高比推力のイオンエンジンを駆動すれば,ソーラーセイルと合わせたハイブリッド推進となり,このコンセプトを踏まえることで,外惑星領域探査が可能となる.本論文では,IKAROSのミッションを紹介し,ソーラー電力セイルによるトロヤ群小惑星探査を提案する.

ソーラー電力セイルは,ソーラーセイルの一部を薄膜太陽電池とすることで,光子加速と同時に太陽光発電も行う日本独自のアイデアであり,IKAROSにより世界で初めてこれを実証した.薄膜太陽電池の電力を用いて高比推力のイオンエンジンを駆動すれば,ソーラーセイルと合わせたハイブリッド推進となり,このコンセプトを踏まえることで,外惑星領域探査が可能となる.本論文では,IKAROSのミッションを紹介し,ソーラー電力セイルによるトロヤ群小惑星探査を提案する.

ソーラー電力セイルは,ソーラーセイルの一部を薄膜太陽電池とすることで,光子加速と同時に太陽光発電も行う日本独自のアイデアであり,IKAROSにより世界で初めてこれを実証した.薄膜太陽電池の電力を用いて高比推力のイオンエンジンを駆動すれば,ソーラーセイルと合わせたハイブリッド推進となり,このコンセプトを踏まえることで,外惑星領域探査が可能となる.本論文では,IKAROSのミッションを紹介し,ソーラー電力セイルによるトロヤ群小惑星探査を提案する.