Abstract: A scanning sensor system includes a light sensor and a scanning telescope having a first telescope subassembly and a second telescope subassembly. Each of the telescope subassemblies has a primary telescope mirror oriented to receive an incident light beam over an angular viewing range as the primary telescope mirror is rotated about a primary-mirror rotation axis, and at least one additional telescope mirror positioned to receive a reflected light beam from the primary telescope mirror. A primary mirror drive rotates the primary telescope mirrors about the primary-mirror rotation axis at a primary mirror angular instantaneous rate of rotation. A half-angle derotation mirror has a derotation-mirror axis parallel to the primary-mirror rotation axis. The half-angle derotation mirror is positioned to reflect light in the optical path when each primary telescope mirror is within the angular viewing range and to direct the reflected image along the optical path toward the sensor.