Earth-to-space laser beam transmission for spacecraft attitude measurement

A method for attitude determination of spacecraft by means of an optical technique is presented in which a laser beam is transmitted from a ground station and detected by a TV camera on a satellite. The principle of determining three attitude parameters using the sequential multiple spot images of the laser beam transmitter appearing in the TV camera's image plane is discussed briefly. Experiments of attitude determination by this method have been conducted, where a TV camera onboard the Japanese Engineering Test Satellite-3 (ETS-3) and a ground-based optical station were used. In the experiments, argon laser transmission from the earth to space and satellite observation by the optical system were done simultaneously. The attitude of this satellite, i.e., a set of pitch, roll, and yaw angles, was determined with high accuracy for some orbits, which permitted us to evaluate the three-axes attitude control system and some attitude control experiments of the satellite.