Toshio Kamiya

Preshaping profiler for flexible spacecraft rest-to-rest maneuvers

Abstract A new feedforward algorithm for flexible spacecraft maneuvers is presented. We call this preshaping profiler the nil-mode-exciting (NME) profiler. This algorithm is designed particularly for single-axis rest-to-rest rotational maneuvers (switching maneuvers) with linear actuators. Generally spacecraft with large flexible structure has a lot of large-mass flexible-modes. Therefore, uncertainity of high-order modes needs to be considered for high-accuracy controller design. This paper presents an extra-insensitive maneuvering method which overcomes above-mentioned difficulties. This algorithm includes a preshaping profiler formulated from sampling function (also known as sinc function), consequently feedforward control inputs generated from the preshaping profiler have no frequency response above a certain designed frequency. Therefore residual vibration at the end-point of maneuver can be highly reduced with minimum loss of maneuver agility.

Evaluation of ground and orbit microvibration of OICETS

Abstract The microvibration excited by on-board instruments is considered as a major factor of pointing stability deterioration. Therefore it is important to estimate the influence of the microvibration on pointing stability before the launch. In this paper, the ground test data obtained by using OICETS MTM (Mechanical Test Model) and in-orbit measured data obtained by on-board accelerometer (MVE: Micro Vibration Equipment) are analyzed. Analyzing these data with appropriate assumption, the transfer characteristics from main disturbance sources to MVE are calculated in both ground and in-orbit cases. As a result, similarity between the ground test data and the in-orbit data is evaluated, and the effectiveness of the ground test in predicting in-orbit microvibration environment is verified.

Comparison of Preshaping Profilers for Reducing Residual Vibrations After Rest-to-Rest Maneuvers

Generally, spacecraft with large flexible structures have multiple flexible modes with large effective masses and various mode shapes; therefore, the presence of uncertain high-order flexible modes should be considered in high-accuracy controller design. However, most researchers have proposed input preshaping algorithms that are valid only for a few flexible modes. Consequently, when these algorithms are applied to a flexible spacecraft having uncertain high-order flexible modes, residual vibrations might not be reduced sufficiently. This paper presents a smooth feedforward control algorithm for rest-to-rest maneuvers that significantly reduces residual vibrations at the endpoint of a maneuver. The new preshaping profiler is based on a filtering technique that combines a pair of sinc functions. The new profiler is compared to several conventional preshaping profilers. In addition, residual vibrations at the endpoint of maneuvers in the presence of unknown higher modes are found to be much smaller than th...

Simulation and Analysis of Satellite Dynamics with Flexible Wire Antennas and Nutation Damper

The dynamics analysis and simulation of a spinning satellite with four flexible wire antennas and nutation damper is presented in this paper. The dynamics of a spinning satellite with flexible appendages has been one of the greatest interests in spacecraft dynamics. Such a configuration is widely and mostly adopted for science satellite with electric or magnetic field antennas. This paper presents the extended analysis done for such a satellite as a part of the preliminary design consideration for the ERG (Energization and Radiation in Geospace) satellite. The ERG satellite also has four wire antennas and a pair of extendable masts for electric and magnetic field measurement. In this analysis, the presence of nutation damper is considered. It is expected that the nutation damping mechanism can also have energy dissipation effect on the motions of the flexible antennas for some of the antenna oscillation modes are coupled with the nutation mode. The study presented in this paper first took an analytical approach to reveal the characteristics of the motions of the wire antennas. The second part shows its application to the ERG satellite and nonlinear simulation results. The analysis gives us the insight of the behavior of the wire antennas under the presence of a nutation damper.

Flexible Spacecraft Rest-to-Rest Maneuvers with CMGs Parallel Gimbal Arrangement

A feedforward control algorithm for flexible spacecraft rest-to-rest maneuvers with CMGs (control moment gyros) parallel gimbal configuration is presented. Single-gimbal CMG cluster in parallel gimbal arrangement has singularity problem and output torque vector is constrained in a 2-DOF plane normal to gimbal axis. This CMGs parallel gimbal configuration is suitable in case that spacecraft has 2-DOF pointing requirement like a Japanese satellite called Astro-G (‘space VLBI’ = radio telescope observation satellite). A CMG guidance law presented in this paper is designed particularly for single-axis rest-torest rotational maneuvers for a flexible spacecraft with 2-DOF pointing requirement. Generally spacecraft with large flexible structure has a lot of large-mass flexible-modes. Therefore, uncertainity of high-order flexible-modes needs to be taken into account for highaccuracy controller design. Most researcher propose input preshaping algorithms with finite target flexible-modes and limited frequency tolerances, so if we apply these algorithms into an actual large flexible satellite, control errors might be theoretically inevitable. The NME (Nil-Mode-Exciting) profiler shown in this paper includes an extra-insensitive preshaping profiler which overcomes above-mentioned difficulties. The NME profiler is a preshaping profiler constructed from a pair of sampling functions (also known as sinc function), consequently feedforward profile generated from this profiler has no frequency response above a certain designed frequency. Therefore residual vibration at the end-point of maneuver can be highly reduced with minimum loss of maneuver agility. Flexible spacecraft dynamics model of Astro-G including 4-CMGs and 4-RWs is used to evaluate the proposed algorithm.

Stepping Motor Driving Disturbance Test and Identification of Mathematical Disturbance Model

Abstract Stepping motor is one of the biggest disturbance sources which generate high-frequency vibration and deteriorate pointing stability of satellite attitude. Those disturbance sources need to be carefully designed not to generate undesirable vibrations. Therefore, in the design of the disturbance sources, we need both of a high-frequency vibration control method and an accurate mathematical disturbance model. For this reason, we tested a stepping motor and evaluated the data of driving disturbance vibrations and identified “stepping motor mathematical disturbance model”. Consequently, we realized an accurate mathematical disturbance model of stepping motor which includes harmonic drive as the motor gear and flexible structure as the inertial load. This mathematical model can be applied to all stepping motors in which key parameters of stepping motor stiffness characteristics and inertial load structural characteristics are given.