• Control Logic
• Earth Horizon Detection
• LEO orbit

IRES N2 represents the current state-of-the-art of Leonardo Company’s high accuracy Earth horizon detection sensors being used in GEO Telecommunication satellites and in the GALILEO GNSS Constellation. It is based on the use of four infrared pyroelectric detectors, for the detection of the Earth horizon, that scan the Earth in the 14 ÷ 16 µm wavelength band. The scanning is carried out by means of a chopper mechanism, which is necessary to have a variable radiative scene in front of the detectors.
The Infrared Earth Sensor “Coarse” product, named IRES-C, is a new configuration suitable to be used for the Earth Pointed Safe Mode on LEO Satellites. IRES-C is a medium accuracy Earth Horizon sensor, that will work at a nominal altitude 625 km while able to cover a range of 400 ÷ 850 km with slightly degraded performance.
In this thesis an improved 3D geometrical model of the IRES-C and Earth system has been developed. The model represents the real intersections between the detectors field of view “rays” and the Earth surface. The actual radiative energy exchange between the detectors and the Earth, in terms of view factors, is also exploited in order to properly estimate the Earth power collected by the pixels and thus simulate the correct pixels output signals.
A dedicated full Control Logic was then developed, with the aim of managing the pixels’ output signals through dedicated algorithms, which estimate Earth azimuth and nadir coordinates and thus the satellite attitude. The control logic can manage the nominal cases when all pixels signals are available, even if affected by Sun or Moon presence. It can be applied also on the non-nominal cases, when some of the signals are not available (for instance because of spikes or anomalies). The thesis has also addressed the issues concerning the ability of the control logic to manage mismatching signals that can be generated by the sensor at end of life.