RAPID READOUT SYSTEM FOR SOLAR POINTING SENSORS

THE PURPOSE OF THIS PROJECT WAS TO INVESTIGATE A SYSTEM FOR RAPIDLY READING AND PROCESSING PHOTOMETRIC DATA FROM LINEAR CHARGE-COUPLED-DEVICE (CCD) ARRAYS USED AS SOLAR TRACKING SENSORS. FOR APPLICATIONS TO POINTING PAYLOADS, THE SYSTEM MUST DETERMINE SOLAR ASPECT ANGLE WITH AN ACCURACY OF 0.4 ARC-SECONDS WITH UPDATES AVAILABLE AT 4 MILLISECOND INTERVALS. SINCE TRACKING FUNCTIONS TYPICALLY USE A SMALL SUBSET OF THE SENSOR PIXELS AND THE APPROXIMATE LOCATION OF THIS SUBSET CAN BE DETERMINED FROM THE PREVIOUS SCAN, THE READ TIME CAN BE REDUCED BY CLOCKING THE UNWANTED PIXELS AT A VERY RAPID RATE. THEREFORE, CIRCUITS WERE DESIGNED TO READ THE CCD ARRAY AT TWO RATES: AT A SLOW RATE (13 KHZ) FORPIXELS NEAR THE SOLAR EDGE AND AT A HIGH SPEED (3.3 MHZ) FORTHE REMAINING PIXELS. THE DUAL READ-OUT RATE SCHEME WAS TESTED DURING PHASE I USING A LINEAR CCD ARRAY ILLUMINATED BY A HELIUM-NEON LASER WITH A KNIFE EDGE IN THE BEAM TO SIMULATE THE SOLAR EDGE. THESE TESTS DEMONSTRATED THE FEASIBILITY OF THE DUAL-RATE, READ-OUT TECHNIQUE FOR SOLAR EDGE TRACKING AND SHOW THAT THE REQUIRED UPDATE RATE CAN BE ACHIEVED WITH LOW-POWER LEVELS FOR CONTROL AND DATA ACQUISITION.