The objective of THASSID (Terminal Homing Applications of Solid-State Imaging Devices) is to develop an advanced optoelectronic solid-state seeker with true fire-and-forget capability. The system comprises an image intensified CCD camera mounted on a gimbaled, momentum-stabilized platform and a digital tracker of advanced design. The camera employs a 490 x 327 picture element CCD array encapsulated in a focused electron tube. This paper describes the composite tracker containing three major subsystems: adaptive gate centroid tracker, correlation tracker, and moving target tracker. System operation is controlled by a Texas Instruments SBP 9900 microprocessor with substantial portions of the tracking algorithms allocated to the microprocessor. Microprocessor support of the composite tracker includes adaptive image quantization, correlation feature selection, feature update, feature replacement, scene stabilization computations':, control of electronic de-zoom, centroid gate position, size, and thresholding, and moving-target-tracker search algorithms. The microprocessor also establishes the operating mode of the correlation tracker and its role in relation to the other tracking subsystems. During the terminal impact phase of the mission the correlation tracker is the primary tracking subsystem. A system incorporating these concepts was delivered to the U. S. Army Missile Research and Development Command for testing and evaluation.