M. C. Natori

Dynamic Behavior of a Tethered System with Multiple Subsatellites in Elliptic Orbits

Dynamic behavior of a tethered system with multiple subsatellites subjected to both atmospheric drag and changes of gravity gradient in elliptic orbits is investigated. The tethered system is modeled as a combination of rigid-body subsatellites and lumped tether masses, and flexibility of the tether is considered. The results of the numerical experiments show that the libration of the total system can diverge due to the atmospheric drag, and the total system begins tumbling motion later. The physical interpretation is clearly presented by focusing on the deviation from the periodic motion. Effects of the atmospheric drag on the attitude motions of the subsatellites and the tension states of the tether are also investigated. It is shown that the large perturbations can cause partial slack states of the tether, which causes unstable attitude motions of some of the subsatellites.

New Deployable Membrane Structure Models Inspired by Morphological Changes in Nature

Some characteristics of morphological changes in nature are discussed and morphological changes in space structure systems are investigated. Essentially space structure systems change their forms and functions, since they must be initially stowed due to spatial constraints of transportation systems, and deployed in their designed orbits. Recently various concepts of membrane structures are proposed for future large space systems, since they can be compactly stowed, and can easily realize space structures with large area. In their developments, it is a major important issue to ensure the reliability of their deployment processes. From the viewpoint of deployment processes, various morphological changes of some plants, insects, and animals are investigated. The efficient characteristics in their morphological changes such as high redundancy, sequential deployment, utilization of gravity forces, and so on are introduced. A new concept of deployable membrane structure models derived especially from the observation of insects’ metamorphosis including eclosion of butterflies, dragonflies, cicadas, and so on is proposed. Numerical results of its deployment behavior are also shown.

Sensitivity Analysis Method for Membrane Wrinkling Based on the Tension-Field Theory

This paper presents a new method for the sensitivity analysis of membrane wrinkling based on the tension-field theory. This method can be applied to design membrane structures to reduce the occurrence of wrinkles. In this method, the wrinkle intensity in a partly wrinkled membrane is evaluated from an apparent strain energy resulting from the deformation through wrinkling. This wrinkle intensity is used as an objective function for wrinkle-reduction membrane design. Further, the sensitivity of the wrinkle intensity with respect to an arbitrary design parameter is derived by employing a semi-analytical differentiation technique and is used to resolve the minimization problem of the objective function. Some design examples show that this minimization problem can be effectively resolved by the proposed sensitivity analysis method and the occurrence of membrane wrinkles can be considerably reduced by minimizing the wrinkle intensity.

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.

Membrane Modular Space Structure Systems and Deployment Characteristics of Their Inflatable Tube Elements

Basic study on membrane modules actuated by inflatable tubes to fit to future hierarchical membrane modular structure systems is introduced. Extended geometrical consideration on folding patterns of membrane structures is investigated considering dual property of tessellated planar surfaces, and deployment behavior of refined laboratory scale module models actuated by inflatable tubes with zigzag folding pattern and with modified zigzag folding one is presented. It is shown that some typical folding patterns for deployable membrane structures can be interpreted through geometrical basis, and that the hexagonal deployable module model with inflatable tubes with modified zigzag folding has stable deployment characteristics.

Design of articulated extensible mast systems and their mechanical characteristics

Compact and reliable mechanical design of articulated extendible mast systems capable of higher structural performance for present and future space development is presented. Functions of an articulated extendible/ retractable mast system with chain drive deployment mechanisms have been proven in space, and another articulated extendible mast system with screw jack mechanisms has been developed as actual flight hardware. Various considerations to get better articulated masts obtained through many kinds of tests and corresponding structure analysis in these developments are shown in detail.

Adaptivity demonstration of inflatable rigidized integrated structures (IRIS)

Abstract An inflatable rigidized integrated structure (IRIS), which is composed of membrane elements and cable networks, and whose structural accuracy is decided by mainly cable networks, has various design adaptivity, since it is a high performance deployable structure for future space applications. In order to keep some stiffness after deployment, materials of membrane are assumed to be rigidized in space, and sometimes the cable network is also rigidized. The concept can cover various structural elements and structure systems. The accuracy analysis of reflector surface constrained by inside hard points and the manufacturing of a simple reflector model is introduced. Test results of rigidized cable columns to show many variations of IRIS to be feasible are also reported.

Stepwise deployment of membrane structures with rolled-up booms: Experiments and simulations

In this paper, simple deployable structures are introduced, which consist of polygonal membranes and elastic booms deployed by only releasing the rolled-up booms in stepwise manners. The membranes are folded up with modified spiral folding patterns to fit the arrangement of booms. The booms are newly-developed bi-convex tapes covered by braids. Basic mechanical test results of the booms are first presented. Deployment experiments of a small conceptual model are demonstrated for several configurations. Numerical simulations of the deployment experiments are also performed employing multi-particle approximation method for membranes and a discrete model for one-dimensional continuum for the booms. The results are compared with the experimental results and the deployment behaviors of the structures are discussed.

Deployable membrane structures with rolled-up booms and their deployment characteristics

1 Visiting Professor, Advanced Research Institute for Science and Engineering, 3-4-1 Okubo / 55S-608, Associate Fellow AIAA 2 Research Associate, Department of Modern Mechanical Engineering, 3-4-1 Okubo / 59-314 ; presently, Assistant Professor, Department of Mechanical, Aerospace and Materials Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran, Hokkaido 050-8585, Japan, Member AIAA 3 Assistant Professor, Department of Space Flight Systems, 3-1-1 Chuoh-ku Yoshinodai, Member AIAA 4 Chief Engineer, 14-10 Shimoyasuta, Maruoka-cho, Member AIAA 5 Professor and Dean, 3-4-1 Okubo, Member AIAA Deployable Membrane Structures with Rolled-up Booms and Their Deployment Characteristics

Quantifying Square Membrane Wrinkle Behavior Using MITC Shell Elements

For future membrane based structures, quantified predictions of membrane wrinkling behavior in terms of amplitude, angle and wavelength are needed to optimize the efficiency and integrity of such structures, as well as their associated control systems. For numerical analyses performed in the past, limitations on the accuracy of membrane distortion simulations have often been related to the assumptions made while using finite elements. Specifically, this work demonstrates that critical assumptions include: effects of gravity, supposed initial or boundary conditions, and the type of element used to model the membrane. In this work, a 0.2m x 0.2m membrane is treated as a structural material with non-negligible bending stiffness. Mixed Interpolation of Tensorial Components (MITC) shell elements are used to simulate wrinkling behavior due to a constant applied in-plane shear load. Membrane thickness, gravity effects, and initial imperfections with respect to flatness were varied in numerous nonlinear analysis cases. Significant findings include notable variations in wrinkle modes for thickness in the range of 50 µm to 1000 µm, which also depend on the presence of an applied gravity field. However, it is revealed that relationships between overall strain energy density and thickness for cases with differing initial conditions are independent of assumed initial conditions. In addition, analysis results indicate that the relationship between wrinkle amplitude scale (W/t) and structural scale (L/t) is independent of the nonlinear relationship between thickness and stiffness.