Abstract: A solar reference flight roll position sensor is mounted on a flight vehi having a longitudinal flight axis. The sensor, a photodetector, senses the angular position of the vehicle with respect to the sun about the flight axis. The sensor includes a lateral effect photodiode for generating first and second photocurrents in response to the position of a beam of sunlight illuminating the active surface of the photodetector. An opaque screen having an aperture is superimposed above the surface of the photodetector such that a different section of the surface is illuminated by sunlight passing through the aperture for different roll angles of the vehicle. The photocurrents are processed to form a discriminant that is a function of roll position. Roll rate is determined by measuring the rate of change of the roll position.