A 'Microprocessor =Trolled OCD Starsensor ('!OAST)

The TPD Off-Axis Star-Tracker (TOAST) aims at achieving a high accuracy of 1.5 arcsec in a 5.4°x8.1° field of view, combined with random pointing capability. This requires a guide-star limit of msilicon = 6.5, giving a 99% probability of finding at least two guide-stars in the field of view, thus permitting 3-axes attitude reconstitution. To enhance the usefulness of the sensor three modes of operation are provided, enabling respectively a survey of the starfield, guide-star acquisition and fine tracking. The sensor is based on a 576 x 385 elements CCD detector. A microprocessor electronics enables an efficient organization of the detector readout and starimage processing, rendering subelement starposition accuracies. The detector is cooled thermo-electrically. A functionally representative breadboard model was built and subjected to performance tests. Test results show that the measured performances are not far from the design goals.