Infrared Horizon Sensors for Attitude Determination

Abstract

Earth orbiting satellites usually require some means of determining their attitude with respect to the earth, either for control or monitoring purposes. Infrared sensors which detect the sharp thermal discontinuity at the earth-space horizon have been developed for this purpose and are being used in a number of American satellite systems. They may be classed under three general types, namely: conical scan sensors, horizon edge trackers, and radiometric balance sensors. The principles of operation of these general types, and examples of flight hardware are briefly described. The relative advantages and dis-advantages of the different types with respect to system application is discussed. Means for minimizing errors caused by cloud cover and horizon gradients are discussed and some data on flight performance given.