The Retroreflector Field Tracker (RFT) is an electro-optical position-measuring instrument which is part of the Dynamic Augmentation Experiment (DAE) to be used on the Solar Array Experiment (SAE), a NASA Marshall Space Flight Center (MSFC) experimental shuttle payload. The tracker measures and outputs the position of 23 reflective targets placed on a 32-meter solar array to provide data for determination of the dynamics of the lightweight structure. As such, the RFT is a noncontact optical position sensor that can be used in applications such as large space structure alignment, rendezvous and docking, and surface figure control of large antennas. The basic sensor operation, tracking logic, and position algorithms are extensions of concepts developed for star tracking. The solid-state sensor uses a 256 x 256 pixel charge injection device (CID) detector; the processor electronics employ three Z-80 microprocessors. The RFT includes a pulsed laser diode illuminator to project light onto retroreflective tape targets on the solar array. The RFT measures position to within *3 millimeters for all targets on the 32-meter array, resulting in an angular resolution of 19 arc seconds (1 sigma). The data output consists of target number, boresight angles, and orbiter coordinates. The data output rate is 2 hertz. The RFT is scheduled to be flown as part of the OAST-1 payload on Space Shuttle flight 41-D in Summer 1984.