A Novel Digital Sun Sensor: Development and Qualification for Flight

Abstract

A novel low-cost Digital Sun Sensor (DSS) is under development for use in Attitude Measurement and Control Systems for Spacecraft. The work, carried out in the frame of a technology program from ESA (European Space Agency), aims for an European, commercially attractive sunsensor with high accuracy. Demands for such a sensor come from future telecommunication missions, but the sensor is suitable also for other type of applications. The device is a sun tracker, that provides the Attitude and Orbit Control Subsystem of the spacecraft with highly accurate sunposition information, in missions from LEO to deep space (0.3 AU to 50 AU) The sensor autonomously provides two-axis attitude information from a single optical head, built around a CMOS Active Pixel Sensor (APS). The field of view (FOV) is 128° x 128°, with an accuracy of 0.01 degrees of arc (1σ) and a resolution of 0.01 degrees of arc in the whole FOV. Other important characteristics are albedo immunity, high radiation tolerance, SEU free and latch-up protection. The main DSS constituents are: • Optical front end, which uses an Active Pixel Sensor with on-chip AD conversion and a pin-hole type aperture, attached directly to the APS. • Electrical front-end, installed on a flex-rigid PCB with electronics for control of the APS detector and for video processing, embedded in a Field Programmable Gate Array (FPGA). • DC-DC converter for internal power regulation. • A housing with mechanical interfaces, alignment cube and connectors for power, data and test interfaces. An Engineering Model (EM) of the DSS has been developed and exposed to a program of functional and pre-qualification tests in vacuum and in a wide temperature range (-50°C to +80°C). The testresults demonstrate, that sensor capabilities comply with the target requirements for accuracy and resolution. The development of a Protoflight Model (PFM) of the sensor is in progress. This PFM will be exposed to an extensive flight qualification program to validate the design versatility for use of the sensor in demanding telecommunication, navigation and earth observation / science missions. Upon successful completion of the PFM program, the unit will fly as a technology experiment on board the European PROBA-2 spacecraft.