Planet–Sun Sensor Revisited

Since the seminal work of Daniele Mortari (“Moon-Sun Attitude Sensor,” Journal Spacecraft and Rockets, Vol. 34, No. 3, 1997, pp. 360–364), concept an attitude sensor using images illuminated celestial bodies has been pushed forward through years. The basic idea consists extracting two independent directions from image a body, namely, camera-to-planet planet-to-sun directions. former is estimated center ellipse fitted to imaged limb points latter symmetry axis region. These assumptions, however, only hold for far-distant spherical targets. In this work, problem reformulated in framework projective camera transformations quadrics conics, algorithm estimating line sight planet illumination direction terminator ellipses, respectively, presented. method applicable any ellipsoidlike body having known orientation. first validated on synthetically generated then tested real pictures Dione Enceladus satellites gathered Cassini spacecraft. Results show that returns rms errors order angular width pixel computing nadir direction, subdegree accuracy sun direction.