Device for determining relative angular position between a spacecraft and a radiation emitting celestial body

Signals indicative of the relative angular position between a spin stabilized spacecraft, probe, or sounding rocket and a radiation emitting celestial body are derived with a detector including four electrodes for deriving indications of the centroid of the radiation image on the detector. During each spin of the satellite each electrode derives a signal having a first non-zero level while the detector is not illuminated by the radiation, and a sound non-zero level while it is illuminated by the radiation.