Yasuyuki Miyazaki

Technology of deployable space structures is necessary for spacecraft to challenge advanced missions. It is important in designing the deployable space structures that they are easily deployable and reliably repeatable. Traditional approach for improving the repeatability was conducted by investigating errors and its effect to the deployment. However, the traditional approach has a problem that results change depending on estimation of the errors. With that background, this study proposes numerical methods to enable selection of robust deployable structures against the errors. The repeatability is decreased due to occurrence of the buckling caused by the errors. Therefore, a structure not occurring the buckling should be selected for designing of a reliably repeatable structure. The buckling is detected by non-positive eigenvalues of a stiffness matrix of the structure in static analysis. However, detection of the buckling in dynamic analysis is difficult because the eigenvalue is also non-positive when the structure has rigid-body motion. This study solved the problem by proposing a method to discriminate the buckling from the rigid-body motion. Furthermore, a method to evaluate instability of the structure quantitatively is desired when only structures occurring the buckling are available for the spacecraft. When the buckling occurs, small disturbance sets off grave displacement. Therefore, this study proposed the method to evaluate the instability quantitatively by calculating disturbance force and buckling displacement as index values of the instability based on the equation of motion. Finally, it was confirmed that the proposed methods are appropriate by the dynamic analyses of truss arch.

This paper derives closed-form solutions for the local deformation of a bi-convex boom under circular bending, and the resulting strain energy and self-extending force. Convex tapes and bi-convex booms that consists of a pair of convex tapes can be stored into a small volume and have high specific rigidity. They extert a self-extending force when stored cylindrically. Therefore, they have been proposed as members of deployable space structures. In this paper, two types of bi-convex booms are considered. In the first, the tapes of the bi-convex boom are bonded to each other at their edges; in the second, the tapes are wrapped in a cylindrical braid mesh. The latter is called a BCON (braid-coated bi-convex) boom. The tape of a BCON boom can slip on each other, and do not separate from each other because of the tension of the mesh net. Consequently, the BCON boom can be used in an ultralight self-deployable structure with quite high stowage volume efficiency and specific rigidity. However, structures using convex tapes or BCON booms have been designed and developed through a trial-and-error process because there is no appropriate formula for the self-extending force of convex tapes. This paper proposes a formula for the deformation of a convex tape that is initially bent into a circular shape. The deviation from the circular shape is obtained by solving the equilibrium equations. The deformation of a bi-convex boom is also derived by using the solution for a convex tape. Thus the theory described in this paper contributes to the design of space structures using convex tapes in bi-convex booms, as well as to the structural mechanics of flexible beams.

A space inflatable extension mast designed on an idea of structural rigidization simulation system has been projected and provided to verify its engineering technology and to obtain the structural property for a long-term operation in space environment. The inflatable mast extended successfully in orbit, and has sent the telemetry data for more than seven months, so far. The experiment progress meets both its minimum and full success criteria for this mast. The simulation model of this mast is made up based upon the ground test, and predicts the natural frequency in orbit. Lightweight extendible masts are fundamental and essential structural elements to construct space structures; therefore a pivotal first step of conditions to utilize space inflatable structures has been actually achieved.