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Closed-loop systems have been developed for controlling the flow above a three-dimensional turret while the hemispherical top of the turret rotates about the pitch axis. Separation and concomitant turbulence levels incurred through the pitching cycle were altered by suction jet slots circumscribing the aperture, which served as control input; an array of pressure sensors on the turret surface provided the controller with information about the state of the flow above the surface. The control objective was to minimize the separation and turbulence in the dynamic environment created by the articulating turret. The closed-loop control systems included dynamical and measurement-based estimators, regulators, filters, and compensators. These components were developed using both computational and experimental data, and the control systemswere evaluated through a series of control-in-the-loop computation-fluid-dynamics simulations and wind-tunnel runs. The implementation of this suction flow-control system resulted in a decrease of fluctuating velocity over the flat optical aperture. Initial simple proportional and the advanced proportional-integral closed-loop control systems were able to decrease the fluctuating velocity more efficiently than the steady suction of open-loop control. The more-advanced closed-loop controllers showed a better ability to track the trends of the separation and turbulence levels as the hemisphere of the turret pitched. The development of the controller design and numerical demonstration of the closed-loop feedback system is described in a companion paper.