An analysis of the Dahl friction model and its effect on a CMG gimbal rate controller

The effects of friction, represented by the Dahl model, on a CMG rate control system was investigated by digital simulation. The conclusion from these simulation results is that gimbal pivot friction can be a significant effect on the gimbal rate control system. The magnitude of the problem this presents depends on the characteristics of the actual pivot. It would appear from this preliminary look that one solution is to insure that the control system natural frequency is higher by some prescribed amount than the natural frequency of the friction loop

The solar array-induced disturbance of the Hubble Space Telescope pointing system

The investigation of the vibrational disturbances of the Hubble Space Telescope that were discovered soon after deployment in orbit is described in detail. It was found that the disturbances were particularly evident during orbital day-night crossings, and that the magnitudes of the disturbances were considerably larger than the design jitter requirements. This paper describes the process by which the vibrations were characterized and isolated to a particular mechanism. The analysis of the flight data and comparisons with computer simulation results showed that the source of the disturbances was the thermally driven deformation of the solar arrays in conjunction with frictional effects in the array mechanisms. The control system was successfully modified to attenuate the disturbances to tolerable levels pending mechanical and thermal redesign of the solar arrays. The new arrays were installed during the first space telescope servicing mission and, in combination with the enhanced control system algorithm, reduced the disturbances to satisfactory levels

Data Processing on Large Interdependent Networks: an Application for Infrastructure Preparedness, and Restoration

This paper presents a method for validating and transforming data for use in interdependent infrastructure network analysis. Critical infrastructure are interdependent on each other for delivery of services and execution of restoration activities. These interdependencies make infrastructure systems vulnerable to extreme events and highlights the needs for preparedness and response plans. Optimization models have been used to create effective plans using interdependent infrastructure networks. These models require accurate input data. However, many data sources have inconsistencies or errors which inhibit the ability to use such optimization models. This work identifies common errors in input network data and provides a method for processing and correcting these errors. We demonstrate the effectiveness of this method on data representing the transportation network in Juan Diaz town, in Panama