Main requirements for an Autonomous OD/SK system were good ground ephemeris prediction based on on-board orbit measurement and on foreseen maneuvers, no overconsumption and possibility for the ground to take over by uploading orbit measured on-ground, or maneuvers plan.
Trade-off on autonomous orbit determination systems outcomes (ordered from worse to best) :
Pure orbit propagation, Sun & Earth sensor, Star & Earth, Combined Star / Earth sensor, GNSS MOSAIC, GNSS LION.
The chosen ASK strategy is the one currently implemented on-ground because it provides good visibility on the upcoming maneuvers thus allows a good ephemeris prediction, has the same fuel efficiency, is well mastered by the operators.
Validation on the Closed-Loop Functional Validation Bench (software tests) outcomes :
ASK module is validated, APS navigator is not compatible with ASK, MOSAIC and LION navigator are compatible with ASK.
Validation performed on the Closed-Loop Real-Time test Bench outcomes:
RTB includes a MOSAIC, a SPIRENT, a LEON2 implementing the ASK SW, and a RT-Linux computer, two 7 days long tests with chemical & hybrid propulsion confirmed the adequacy of MOSAIC with AODSK in nominal conditions.
Additional tests performed has shown the sensitivity of SK performances to the radial position error which could be reduced by further optimizing the GNSS receiver filter.