Che-Hang Charles Ih

Experiments in multivariable adaptive control of a large flexible structure

A six-input/six-output multivariable adaptive controller is used to control a large 3-dimensional flexible structure experiment. For this purpose, the JPLIAFAL antennalike experiment structure is used, with instrumentation distributed on both the hub and the ribs. This represents a significant increase in complexity relative to earlier adaptive control experiments performed on the same structure, utilizing a two-input/two-output set-up with instrumentation on the hub alone [I]. The increase in instrumentation significantly increases spatial controllability, and excitation and control of a much larger set of modes. This paper documents multivariable adaptive control experiments on this structural configuration, and discusses many of the associated design and implementation issues required for successful operation.

Adaptive control experiment with a large flexible structure

A large space antenna-like ground experiment structure has been developed for conducting research and validation of advanced control technology. A set of proof-of-concept adaptive control experiments for transient and initial deflection regulation with a small set of sensors and actuators were conducted. Very limited knowledge of the plant dynamics and its environment was used in the design of the adaptive controller so that performance could be demonstrated under conditions of gross underlying uncertainties. High performance has been observed under such stringent conditions. These experiments have established a baseline for future studies involving more complex hardware and environmental conditions, and utilizing additional sets of sensors and actuators.

An Investigation of Adaptive Control Techniques for Space Stations

Of all large space structural systems, space stations present a unique challenge and requirement to advanced control technology. Their operations require control system stability over an extremely broad range of parameter changes and high level of disturbances. During shuttle docking the system mass may suddenly increase by more than 100% and during station assembly the mass may vary even more drastically. This coupled with dynamic model uncertainties require highly sophisticated controller and control architectures. An adaptive control algorithm along with the proposed inner-loop plant augmentation for controlling the space station under severe conditions of shuttle docking, mass and inertia change and modal truncation are investigated in this paper. Simulation results with a simplified Initial Operation Center model show that the controller is robust and the plant dynamics closely follows that of the reference model. Reasonable results have been observed even with the constraints of excessive control hardware saturation.

Figure Control Concepts For Segmented Reflector Telescopes

This paper presents an overview of the control analysis activity related to the development of figure control technologies for large space telescopes with precision segmented, actively controlled, primary reflectors. The issues addressed here involve the development of geometric and dynamic models, characterization of figure estimation errors and optimal sensor placement, and the development of quasi-static and dynamic control concepts. The most significant simulation results obtained during an extensive performance evaluation are also presented.

Space Station Adaptive Payload Articulation Control

Abstract A direct input gain weighting concept is developed and added to the existing adaptive control algorithm for more effective control. The effectiveness of this extended algorithm is demonstrated by payload articulation control on board a space station. The reference model is selected based on the required performance and its outputs define the slew commands. The simulation results show that the adaptive controller drives the payloads to track the slew commands nearly perfectly while suppressing the vibration of both the payloads and the station during the slew operation in spite of the model uncertainties associated with the station. Sufficient stability conditions for this extended algorithm are derived

Dynamic Performance Modeling and Stability Analysis of a Segmented Reflector Telescope

In the present paper the problem of vibration suppression in segmented reflector telescopes is considered. The decomposition of the structure into smaller components is discussed and control laws for vibration suppression, as well as, conditions for stability at the local and global levels are presented. The states of the reflector segments are mapped into ray displacements on the detector plane.