Shyh Jong Wang

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.

Dynamics and control of a Shuttle-attached antenna experiment

Study results obtained to date identify the requirements for a large space system flight experiment. This paper considers the dynamics and control of an offset feed wrap-rib antenna attached to the Shuttle for such an experiment. Results reported in this paper are primarily based on the analysis and simulation of the combined Shuttle and antenna flexible dynamics model, and the Shuttle Vernier Reaction Control Subsystem. These results establish the technical feasibility of the Shuttle attached antenna flight experiment. Static and dynamic disturbances examined do not cause significant dynamic interactions to the experiment. Shuttle Vernier jets can be used for control purpose or as controlled excitation sources for experiment. Interface between the Shuttle and the antenna can be rigid or actively decoupled depending on the experiment objective. Key large space systems control technologies such as distributed sensing and actuation, system identification, figure estimation and control, and control for slew or reconfiguration can be validated with the experiment configuration described in this paper.

A Decentralized Approach to Vibration Suppression in Segmented Reflector Telescopes

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 level are derived. These conditions, and the properties of the interconnecting patterns are then utilized to obtain sufficient conditions for global stability.

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

Large Space Structure Experiments on the Space Station: A Systems View

Abstract The Space Station and its accompanying platforms, such as the Earth Observing System (EOS), constitute the initial phase of deployment of large structural systems in space In this paper, four interrelated structural experiments, i.e., system identification, advanced adaptive control, distributed control, and dynamic disturbance control, are proposed as part of in-space technology development. The primary objective here is . to present the underlying approaches and scenarios for large structural system experimentation pertaining to the control aspects, requirements, specifications and overall conditions in which the experiments described can be performed For all four experiments, the strawman test article or experiment apparatus selected to represent generic flexible space structures is a large off-set fed wrap-rib antenna. This choice was made due to the structurally flexible antenna reflector dish whose figure and dynamic interactions with the long boom and feed, during deployment and operation, will require highly sophisticated and precise control and sensing system