Physical Modelling of Sensor FOV Blockages and Hybrid Mode Sensing Based Sun Acquisition

Earth observation imaging spacecraft sometimes have large booms, parabolic reflector or rotating elements for microwave or optical imaging as payload. Such large diameter dish or reflector on top of the spacecraft bus poses a constraint in the FOV of the Sun Sensors which are essential for initial as well as subsequent Sun acquisitions. These large reflectors, booms or payload masses together with the platform edges result in blockages in different planes of the FOV of the prime Sun sensors. Development of end-to-end blockage models together with the inaccuracies help in mitigating the Sun Acquisition, hindered by the FOV Blockages. The current paper brings to light the solution to such static and dynamic blockages in the sensors’ FOV caused by the reflector through the development of Blockage models based on the available angular measurement data. A hybrid mode sensing based acquisition scheme (Fine sensor guided by Prime) is also presented which helps to overcome such FOV clearance issue. Simulations are carried out in MATLAB/Simulink for a typical case for a spacecraft where large 4m diameter reflector in on-orbit deployed condition results in inherent blockage to the FOV of Sun Sensor thereby evolving a twin sensor based acquisition scheme.