Application of preview information to pointing control of truss structure using artificial thermal expansion on orbit

Abstract

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.

Effect of Member Length Uncertainty and Backlash on Deformation Accuracy for a High-Precision Space Truss Structure

“…Their nominal lengths are defined as 380 mm, obtained by referencing the experimental model of previous research. 21) The diagonal rods are composed of aluminum cables with a diameter of 2 mm, and are assumed to support only the tension force. Thus, the stiffness is set as zero for the compression load.…”

“…In addition, as a study to reduce the structural error due to these uncertainties, kinematic coupling is utilized at the connection point between the optical bench and the satellite body to release the distortion generated due to thermal deformation, 20) or attitude control system of the entire optical bench using actuators is utilized. 21,22) However, the amount of the released error is limited. Therefore, it is necessary to clarify the effect of each uncertainty on the shape accuracy of the entire truss structure.…”

Evaluation of dimensional stability of metering truss structure using built-in laser interferometric dilatometer

“…For example, the metering structure of the Hubble Space Telescope is designed with selected low-CTE graphite/epoxy composites to minimize thermal expansion, and actuators on the primary and secondary mirrors are provided to adjust their mirror positions [1]. In another study, heaters were used as actuators and induced the thermal deformation for pointing control in instruments [9]. In order to optimally combine these methods and to achieve high dimensional stability, it is important to accurately evaluate the stability of structures and materials by incorporating a reliable measurement system in the design [10,11].…”

Deployment Repeatability of Pointing Performance for Highly Precise Extensible Optical Bench Considering Uncertainties on Backlash and Friction

“…This EOB with a 6 m length can be folded to store into the fairing of H-IIA, and a fixed optical bench (FOB) with a 6 m length is stored with its shape. 1) The pointing accuracy requirement for the hard X-ray telescope on HITOMI was less than 69 arcseconds. 2) In future space astronomy missions, the pointing accuracy requirement for the optical bench will be strictly reduced to the order of arcseconds.…”