Due to problems in calibrating the sensitivity and relative orientations of the star trackers, IDOP's were rarely successful on Astro-1. Most target acquisitions were done in a manual mode that used the JPL-provided ASTROS Star Tracker (AST) mounted on UIT. The AST is a CCD-based tracker with a large (2.5 2.2) field of view. The AST identifies the three brightest stars in its field and displays the magnitude and coordinates of these stars to the crew. Using the displayed coordinates and a finding chart generated specifically for each target, The PS or MS uses the manual pointing controller to orient the IPS and place the target in the field of view of the HUT TV camera.
Once the target has been acquired, the IPS knowledge of the pointing direction can be updated, but the IPS is not in optical hold after a manual target acquisition. Pointing stability at this point is provided only by the IPS gyros, and tracking for the rest of the observation must be provided by one of the following methods.