ESA GNC Conference Papers Repository
PRISMA-I: an Agile, high Performance AOCS for EO Missions
The PRISMA-I is an Italian Earth Observation satellite combining hyperspectral and panchromatic sensors in a single camera. The payload acquires images of the Earth simultaneously in a large number of spectral bands using an imaging spectrometer in a push-broom mode of operation. The spacecraft has a mass of about 600 kg and it is placed on a frozen sunsynchronous repetitive orbit at 614 Km of altitude. The AOCS design is based on the heritage of the AGILE mission for the part of initial attitude acquisition after the release from the launcher and for the safe mode, but with a great step forward of the pointing performance of more than one order of magnitude (APE of 100 arcsec 3?). This improvement is obtained with the introduction of new fine control modes to support the payload activities. Moreover the capability to perform orbital manoeuvres and fast attitude manoeuvres (any repointing in less than 5 minutes) have been added. This is permitted by an enhancement of the AOCS sensors (APS star sensors, gyroscopes, GPS, magnetometers and sun sensors) and actuators (four reaction wheels in pyramidal configuration, magnetic torquers, thrusters) foreseen in the subsystem architecture and by implementing new AOCS algorithms. The requirements of this mission and of other missions actually under study in CGS S.p.A. have been merged to create an envelope on which to base an AOCS high level architecture design. This design can be used for a range of different missions, when high pointing performance and a high agility is required, as for Earth and Deep Space Observation missions. This is done through an appropriate design of the AOCS logics implemented in the AOCS state machine, which has been ideated to support this wide range of possible missions.