Naoto Ogura

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.

A New Method of Testing Advanced Spacecraft Pointing Control Involving Flexibility

In response to the strong need to demonstrate the validity of newly developed satellite attitude control logics, a new ground test method has been developed. This test method features a scale model called SSDM (Scaled Satellite Dynamic Model). SSDM behaves just like a satellite released in non-gravity field and serves as the satellite attitude dynamics portion in the control loop. This test method enables on-ground dynamic qualification of advanced control laws which so far has been unavailable. As the first application of this method, robust filter control loop for MUSES-B satellite has been tested

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.