  Sun sensors are an integral part of the attitude and orbit control system
onboard almost any spacecraft. While the majority of standard analogue sun
sensors is based on photo-detectors which produce photo-currents proportional
to the cosine of the incidence angle (cosine detectors), we propose an
alternative scheme where the vectorial photoelectric effect is exploited to
achieve a higher sensitivity of the sensed photo-current to the incidence
angle. The vectorial photo-effect is investigated in detail for metal cathode
detectors in a space environment. Besides long operational lifetimes without
significant degradation, metal cathode detectors are insensitive to earth
albedo, which may significantly reduce the errors affecting attitude
measurements in low earth orbits. Sensitivity curves are calculated and
trade-offs performed with the aim of optimizing the sensitivity whilst also
providing currents sufficient for detection. Simple applications and detector
configurations are also discussed and compared to existing designs.
