Horizon sensor

Abstract

A family of two axis horizon sensors using the same basic scan technique is provided which achieves a relatively wide altitude range with a minimum of moving parts for performing vehicle attitude control and guidance. The horizon sensor for indicating the orientation of a space vehicle senses a line of discontinuity in optical radiation between a reference planet and outer space in at least two planes using a single sensor which includes a single detector means for detecting the optical radiation. The detector is scanned across the line of discontinuity in at least two planes. The scanner includes a rotary element driven by a single motor having at least two stationary reflecting elements positioned therearound. A phase reference signal generator is coupled to the motor and driven in synchronism therewith for generating at least two reference signals at predetermined points in the scan. Electronic circuitry is provided utilizing the reference signals and the signals generated by the detector for measuring rotational intervals between the reference signals and the detector signals for determining the attitude of the sensor in the two mutually perpendicular axes. The stationary reflecting mirrors may be two, three or four in number each of which scans the detector over a different pattern across the planet used as a reference for attitude control. Advantageously, in accordance with the present invention, the family of two axis sensors requires only one sensor head, one scanning motor, one detector all of which are housed in one package.