Systems using inertia wheels are evaluated in this report to determine their suitability for precise attitude control of a satellite and to select superior system configurations. Various-possible inertia wheel system con-figurations are first discussed in a general manner. Three of these sys¬tems which appear more promising than the others are analyzed in detail, using the Orbiting Astronomical Observatory as an example. The three sys¬tems differ from each other only by the method of damping, which is provided by either a rate gyro, an error-rate network, or a tachometer in series with a high-pass filter.nAn analytical investigation which consists of a generalized linear analysis, a nonlinear analysis using the switching-time method, and an analog computer study shows that all three systems are theoretically capable of producing adequate response and also of maintaining the required pointing accuracy for the Orbiting Astronomical Observatory f ±0.1 second of arc. Practical considerations and an experimental investigation show, however that the system which uses an error-rate network to provide damp¬ing is superior to the other two systems. The system which uses a rate gyro is shown to be inferior because the threshold level causes a signifi¬cant amount of limit-cycle operation, and the system which uses a tachom¬eter with a filter is shown to be inferior because a device with the required dynamic range of operation does not appear to be available. The experimental laboratory apparatus used to investigate the dynamic perform¬ance of the systems is described, and experimental results are included to show that under laboratory conditions with relatively large extraneous disturbances, a dynamic tracking error of less than ±0.5 second of arc was obtained.
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