The KD-5100+ is an upgraded higher reliability version of Kaman's proven KD-5100 measuring system and utilizes the identical hybrid microcircuit. The KD-5100+ incorporates upgrades to: circuit layout, ground connections, and sensor connectors, and adds higher reliability diodes and capacitors. The KD-5100+ retains the performance of the KD-5100 system. Two precisely matched sensors of a measuring channel are positioned opposite each other on the back of a Fast Steering Mirror (FSM) in two coordinate axes. As the FSM actuators drive the mirror about the center flexure, the mirror moves away from one sensor of an axis and toward the other sensor by an equal amount. The KD-5100+ output signal is used to actively control mirror position.