Star trackers are opto-electronic sensors used onboard of satellites for the autonomous inertial attitude determination. During the last years, star trackers became more and more important in the field of the <strong>a</strong>ttitude and <strong>o</strong>rbit <strong>c</strong>ontrol <strong>s</strong>ystem (AOCS) sensors. High performance star trackers are based up today on <strong>c</strong>harge <strong>c</strong>oupled <strong>d</strong>evice (CCD) optical camera heads.<p> </p>The Jena-Optronik GmbH is active in the field of opto-electronic sensors like star trackers since the early 80-ties. Today, with the product family ASTRO5, ASTRO10 and ASTRO15, all marked segments like earth observation, scientific applications and geo-telecom are supplied to European and Overseas customers.<p> </p>A new generation of star trackers can be designed based on the APS detector technical features. The measurement performance of the current CCD based star trackers can be maintained, the star tracker functionality, reliability and robustness can be increased while the unit costs are saved.
Star trackers are opto-electronic sensors used on-board of satellites for the autonomous inertial attitude determination. During the last years star trackers became more and more important in the field of the attitude and orbit control system (AOCS) sensors. High performance star trackers are based up today on charge coupled device (CCD) optical camera heads. The active pixel sensor (APS) technology, introduced in the early 90-ties, allows now the beneficial replacement of CCD detectors by APS detectors with respect to performance, reliability, power, mass and cost. The company's heritage in star tracker design started in the early 80-ties with the launch of the worldwide first fully autonomous star tracker system ASTRO1 to the Russian MIR space station. Jena-Optronik recently developed an active pixel sensor based autonomous star tracker "ASTRO APS" as successor of the CCD based star tracker product series ASTRO1, ASTRO5, ASTRO10 and ASTRO15. Key features of the APS detector technology are, a true xy-address random access, the multiple windowing read out and the on-chip signal processing including the analogue to digital conversion. These features can be used for robust star tracking at high slew rates and under worse conditions like stray light and solar flare induced single event upsets. A special algorithm have been developed to manage the typical APS detector error contributors like fixed pattern noise (FPN), dark signal non-uniformity (DSNU) and white spots. The algorithm works fully autonomous and adapts to e.g. increasing DSNU and up-coming white spots automatically without ground maintenance or re-calibration. In contrast to conventional correction methods the described algorithm does not need calibration data memory like full image sized calibration data sets. The application of the presented algorithm managing the typical APS detector error contributors is a key element for the design of star trackers for long term satellite applications like geostationary telecom platforms.
Star sensors developed in the last years can be enhanced in terms of mass reduction, lower power consumption, and operational flexibility, by taking advantage of improvements in the detector technology and the electronics components. Jena-Optronik GmbH developed an intelligent modular star and target named 'stellar and extended target intelligent sensor' (SETIS). Emphasis was placed to increase the sensor adaptability to meet specific mission requirements. The intelligent modular star and target tracker shall generate positional information regarding a number of celestial targets or shall act as a navigation camera. The targets will be either stars or extended objects like comets and planetary objects, or both simultaneously. Deign drivers like simultaneous tracking of extended targets and stars or searching for new objects during tracking of already detected objects require a powerful hard-wired digital data preprocessing. An advanced rad-tolerant ASIC- technology is used for the star tracker preprocessor electronics. All of the necessary preprocessing star tracker functions like pixel defect correction, filtering, on-line background estimation, thresholding, object detection and extraction and pixel centroiding are realized in the ASIC design. The technical approach for the intelligent modular star and target tracker is presented in detail. Emphasis is placed on the description of the powerful signal preprocessing capabilities.