ESA GNC Conference Papers Repository

Selex ES started developing Infrared Earth Sensors for the Earth horizon detection since mid-years '60. Since then several IRES “generations” followed and the IRES N2 represents the current state-of-the-art of SES high accuracy Earth horizon detection sensors, being used in GEO TLC satellites and in the GALILEO GNSS Constellation at MEO Orbit. This new Infrared Earth Sensor Coarse product, named “IRES-C”, is a medium accuracy Earth Horizon sensor, suitable to be used as backup or safe mode unit and configurable for LEO or GEO orbits. The IRES-C can be seen thus a low cost option to the IRES N2 for GEO and MEO orbits, while extending the coverage to LEO orbits, where the IRES N2 cannot operate. The IRES-C product is in fact based on concepts investigated and consolidated in two precedent ESA Contracts, where the IRES-C architecture has been defined and verified by test with an Engineering Model (EM) configured for GEO applications. Feasibility evaluation and architecture for the LEO orbit application have been also studied in the frame of the development contract. In the last period new market opportunities for this product were created by the perceived advantages of using an Earth Sensor for the Earth Pointed Safe Mode on LEO Satellites. To answer to these arising needs, Selex ES studied an IRES-C configuration specifically dedicated to cover this application, thus defining and characterizing a sensor configuration that will work at a nominal altitude of 625 Km but able to cover a range from 300Km to 850Km with slightly degraded performance. At the same time costs saving solutions have been defined, together with ways to ease the use of the unit on board LEO satellites (Digital interfaces, Smart Pitch and Roll reconstruction algorithms and calibration to be done at AOCS level, Simplified stimuli for end to end workmanship verification, etc.). The results of these studies and the final product configuration are described in the paper.