Hiraku Sakamoto

Mission Report on The Solar Power Sail Deployment Demonstration of IKAROS

Hirokata Sawada Japan Aerospace Exploration Agency, Kanagawa, 252-5210, JAPAN Osamu Mori 2 Japan Aerospace Exploration Agency, Kanagawa, 252-5210, JAPAN Nobukatsu Okuizumi Japan Aerospace Exploration Agency, Kanagawa, 252-5210, JAPAN Yoji Shirasawa University of Tokyo, Tokyo, JAPAN Yasuyuki Miyazaki Nihon University, Chiba, 274-8501, JAPAN Michihiro Natori Waseda University, Tokyo, 169-8555, JAPAN Saburo Matunaga Tokyo Institute of Technology, Tokyo, 152-8552, JAPAN Hiroshi Furuya Tokyo Institute of Technology, Tokyo, 152-8552, JAPAN Hiraku Sakamoto Tokyo Institute of Technology, Tokyo, 152-8552, JAPAN

Dynamic Wrinkle Reduction Strategies for Cable Suspended Membrane Structures

The present study addresses vibration mitigation of membrane structures the boundaries of which are surrounded by weblike perimeter cables. This proposed membrane design realizes significant structural mass reduction when compared to the conventional catenary design. A key dynamic characteristic of the proposed structure is that support perturbations propagated into the outer perimeter cables have a minor effect on the vibration frequencies of the membrane. This property has been exploited in the development of vibration mitigation strategies using active control. This is corroborated by carrying out nonlinear transient analysis, which accounts for the effect of wrinkles in the membrane. The results confirm that disturbances emanating from the support structures can be isolated by the outer perimeter cables while maintaining the interior membrane in a wrinkle-free taut condition. A simple active control law has been developed and applied to only the outer perimeter cables. Numerical simulations show that the combination of the web-cable girded membranes and the proposed vibration mitigation strategy can provide sufficient damping for both in-plane and out-of-plane vibrations.

Analysis of Membrane Dynamics using Multi-Particle Model for Solar Sail Demonstrator "IKAROS"

1 Post-doctoral Researcher, JAXA Space Exploration Center, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan. 2 Assistant Professor, JAXA Space Exploration Center, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan. 3 Professor, Department of Aerospace Engineering, 7-24-1 Narashinodai, Funabashi, Chiba, Japan. 4 Assistant Professor, Department of Mechanical and Aerospace Engineering, 2-12-1 Ookayama, Meguro-ku, Tokyo, Japan. 5 Graduate Student, Department of Aeronautics and Astronautics, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, Japan. 6 Assistant Professor, Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan. 7 Post-doctoral Fellow, JAXA Space Exploration Center, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan. 8 Associate Professor, Department of Built Environment, 4259-G3-6, Nagatsuta, Midori-ku, Yokohama, Japan. 9 Associate Professor, Department of Mechanical and Aerospace Engineering, 2-12-1 Ookayama, Meguro-ku, Tokyo, Japan. 10 Visiting Professor, Faculty of Science and Engineering, 55S-608, 3-4-1 Okubo, Shinjyuku, Tokyo, Japan. 11 Professor, JAXA Space Exploration Center, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan. 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 19th 4 7 April 2011, Denver, Colorado AIAA 2011-1890

Finite Element Modeling of Sail Deformation Under Solar Radiation Pressure

Anumerical structural model of a thin-film sail that simulates the deformation caused by solar-radiation pressure is developed, using a geometrically nonlinear finite element method (FEM). By using the finite element presented in this study, the force and moment exerted on an arbitrarily shaped solar sail subjected to solar pressure can be calculated accurately. In addition, it is shown that the sail deformation due to a solar-pressure load can be approximated by the deformation caused by the corresponding uniform gas-pressure load. This finding will significantly simplify analyses to improve attitude controller design as well as structural design of sailcraft, because commercially available FEM software can be used for the analyses.

Transient Dynamic Analysis of Gossamer-Appendage Deployment Using Nonlinear Finite Element Method

The present study develops a new three-dimensional Timoshenko beam finite element (FE) whose length can be varied during transient dynamic analyses. The variable-length element enables the dynamic deployment analysis of flexible appendages with non-negligible bending stiness. In addition, the developed scheme employs an implicit time integration whereby energy and momentum in the system is properly conserved, and no artificial numerical dissipation is introduced. As a result, the scheme makes it possible to evaluate the impact of structural damping on the system’s dynamics. The developed beam element is then used in an FE model of a solar sailcraft currently developed in Japan, and its deployment dynamics is analyzed allowing for the non-zero bending stiness of the bundled membranes, as well as the eect of some realistic design imperfections.

Localized Vibration Isolation Strategy for Low-Frequency Excitations in Membrane Space Structures

The present study explores both structural and controller design to attenuate vibration in large membrane space structures, especially due to low-frequency harmonic excitations. It is very difficult for membrane structures to suppress the low-frequency vibration induced by flexible support structures, because a lightly prestressed membrane has extremely low mode frequencies and little damping effect. The present study proposes the use of weblike perimeter cables around a membrane, and the application of simple and lightweight active controllers only along the web cables in order to isolate the membrane from vibration. This strategy successfully reduces the membrane vibration when the web-cable configuration is appropriately tailored. Both linear and nonlinear finite-element analyses exhibit a clear tradeoff between structural mass and control efficiency.

Distributed and Localized Active Vibration Isolation in Membrane Structures

Once a membrane starts vibrating, suppressing the vibration is very difficult. Thus, the present study primarily aims at isolating a membrane from major disturbance sources, that is, from support structures. The present study introduces weblike suspension cables around a membrane and develops in theory a vibration-isolation strategy applied only along the cables. First, collocated small actuators/sensors are attached at the interfaces of the cables and the membrane to realize a distributed cable-tension control. Second, linear theory-based localized controllers are designed for suspension-cable substructural models. The feedback laws for these two kinds of controllers are derived employing a partitioned equation of motion. The resultant control system is lightweight, simple, low order, robust, and redundant A series of transient analyses using a geometrically nonlinear finite-element method corroborates the effectiveness of the proposed vibration-isolation strategy.

Deflection of multicellular inflatable tubes for redundant space structures

A new concept of redundant space structures using multicellular inflatable elements is proposed, and the results of basic analyses on simple multicellular models are reported. Much effort has been devoted to methods for sufficiently hardening the inflatable elements in space to tolerate damage sustained from space debris, especially with respect to rigidization of a membrane; however, if the structures are redundant, they do not need to be as stiff and strong as those without redundancy. Deflections of two kinds of multicellular cantilever inflatable tubes are numerically investigated. First, nonrigidized tubes are analyzed by the modified Euler-Bernoulli beam theory. Second, rigidized tubes with slackening effects of the membrane are simulated using the modified nonlinear finite element method. The results show that multicellular tubes can be redundant against problems with pressurization and can be as stiff and as strong as monocellular models with less internal gas. In the multicellular rigidized inflatable tubes, maintaining a small amount of internal pressure is quite effective to prevent the deformation of the cross section, which causes a drop in stiffness and strength. Therefore, adopting a redundant system is effective both for rigidized and nonrigidized inflatable elements.

Development of a smart reconfigurable reflector prototype for an extremely high-frequency antenna

A prototype for a space-borne smart reconfigurable reflector, whose reflector surface can be changed intentionally using surface adjustment actuators, has been developed, and its performance was evaluated through experiments. The smart reconfigurable reflector was designed as a sub-reflector of a space antenna for observations in the extremely highfrequency band (frequency range: 30 -300 GHz) and is used for correcting the path length errors in the antenna system caused by surface deformations of the main reflector. It consists of a solid surface, supporting members, and surface adjustment actuators. The surface adjustment actuators are a key part of the smart reconfigurable reflector, and each consists of a piezoelectric stack actuator and a displacement magnifying mechanism. Functional tests were performed in order to investigate the performance of the actuator. The results indicate that the actuator has a stroke of more than 0.9 mm with an accuracy of 0.01 mm and a force of more than 90 N. The control accuracy was much better than the required surface accuracy for an extremely high-frequency antenna system. The effectiveness of the developed reflector system was demonstrated through numerical simulations and shape modification experiments. In order to clarify the effectiveness of the developed smart reconfigurable reflector, the performance of the antenna system, equipped with the smart reconfigurable reflector, was evaluated. The experimental results confirmed the performance expected from the numerical simulation and indicated that the antenna could be adequately controlled as expected.

Deformation Properties of Solar Sail IKAROS Membrane with Nonlinear Finite Element Analyses

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: mechanics of higher out-of-plane stiffness of the IKAROS membrane. Two possible causes are hypothesized in this paper; the bending stiffness increased by the curvature of thin-film solar cells, and the deformation mode changed by the curvature. Although the second moment of area of the sail membrane is calculated by the natural vibration analyses, the effects of the bending stiffness increased by the curvature on the out-of-plane displacement is small. The effects of the deformation mode on the out-of-plane displacement is examined by geometrically calculating the relationships between the sensitivity of the margin in a circumferential length to the displacement. The results indicate that the sensitivity becomes small as the curvature becomes large. Thus, the high out-of-plane stiffness of the IKAROS membrane can be induced by the increased bending stiffness and by the changed deformation mode due to the curvature of the solar cells.