An extendible mast of a space-inflatable structure was used as a scientific probe onboard the sounding rocket S-520-23 launched in September 2007. The inflatable structure extended successfully and worked well as a scientific instrument. This was Japan's first space verification of a space-inflatable structure, and the world's first use of an inflatable structure as a practical antenna. The extendible mast as an inflatable structure is called "SPINAR" (SPace INflation Actuated Rod), and it consists of an extendible rod and inflatable extension mechanisms. The rod, which is an open section tubular member, can be stored around a spool and has the advantage of structural rigidity when extended. The principle of SPINAR is similar to that of STEM (Storable Tubular Extendible Member); however, relatively reduced weight and enlarged rigidity can be achieved in SPINAR if light and rigid composite materials replace the metallic STEM rod. In addition, an inflatable thin film tube is used as the extension actuator instead of an electrical motor for weight reduction, the extension mechanisms are simplified, and the storage and drive mechanism box are downsized. The inflatable tube does not have to be rigidized because of the virtual structural rigidization concept of the outer shell structure of the rod.
The pointing performance of a truss structure on orbit that is used for a large space telescope is discussed. To achieve advanced science missions, large and precise support structures such as truss structures are needed. However, the preciseness of the structure might be lost due to various disturbances on orbit. Therefore, to realize ultra-large and precise support structures, active shape control of the structures is needed. To control the shape, we use artificial thermal expansion caused by heaters instead of mechanical actuators. Control systems without mechanical mechanisms have high reliability, which is very attractive for use on orbit. However, there are some constraints regarding the usage of heaters. The control input is restricted to positive inputs because heaters can give off heat but cannot dissipate heat actively, and there will be upper limits on the heat input. To improve the control performance under such constraints, we apply "Model Predictive Control (MPC)" as a feedforward control method with preview information. In this paper, we mainly show the effectiveness of MPC compared with PI control, which is one of the typical feedback control methods. We developed a structural mathematical model and a thermal mathematical model in order to evaluate the performance of the control system. It is confirmed through numerical simulations that the total error is reduced by MPC compared with PI control.
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