Pseudo and full-gyroless operative modes on board of COSMO-SkyMed mission

COSMO-SkyMed is an Earth Observation space program funded by the Italian Ministry of Research and Italian Ministry of Defence (I-MoD) and conducted by the Italian Space Agency (ASI) in conjunction with I-MoD. COSMO-SkyMed (CSK) consists of a constellation of four Low Earth Orbit mid-sized satellites, each carrying a multi-mode, high resolution, electronically steerable Synthetic Aperture Radar (SAR) instrument operating at X-band and a full featured Ground Segment to properly exploit space capabilities. In the framework of the current programmatic phase concerning the operational management of the constellation, a set of qualified teams was introduced in order to perform technical, operational and engineering activities on the system. Tailored information flows were developed among ASI, It-MoD and Industrial staff in order to continuously guarantee the performances and the availability of the system and to identify potential enhancements and changes for the optimization of the overall cost/benefit ratio and the increase of the performances with respect to the original specification. Thanks to such an organization, many improvements have been identified and implemented. Amongst them, this paper illustrates new operational procedures in order to extend the full operational performance also in case of failure of the gyroscope. The proposed solution implies modifications on the attitude determination algorithms, on the AOCS operational modes transition logic and on the operational procedures adopted in the satellite management from the satellite control centre. The attitude determination algorithm in nominal pointing mode has been extended in order to calculate the spacecraft rate from the Star Tracker quaternion measurements. This approach, detailed in the present paper, is based on the substitution of the measures the failed gyro channels with ‘artificial’ data reconstructed by deriving the attitude quaternion. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.