PREDICTIONS OF THE GOCE IN-FLIGHT PERFORMANCES WITH THE END-TO-END SYSTEM SIMULATOR

摘要

The GOCE payload (constituted by a 3-axis gradiometer and by a 12-channel GPS receiver) has been implemented and characterized to the maximum possible extent on ground. The results of the characterisation tests have been used to complete the high-fidelity models of the GOCE instruments which are included in the GOCE End-to-End (E2E) System Simulator. The E2E Simulator, set up since the early stages of the GOCE programme and continuously updated according to the project evolution, includes in addition accurate models of the satellite linear and angular dynamics and of its perturbations, of the Drag-^sFree and Attitude Control System (DFACS) and of the orbit environment (Earth gravity and magnetic field, atmosphere density and winds at satellite altitude, Sun/Earth radiation, Sun/Moon gravity, GPS satellite constellation). This tool allows simulating the in-flight dynamics behaviour of the satellite in various mission phases and the behaviour/output of the payload instruments during initial set up, calibration and science modes. A post-processing module elaborated the raw measurements using the Payload Data Ground Segment algorithms and provides the Level 1b products of the mission, among which the components of the gravity gradient tensor in the Gradiometer Reference Frame and the GPS receiver measurements, derived positions and reconstituted satellite orbit in Earth-fixed reference frame. The GOCE E2E System Simulator is the tool utilized for producing the most reliable prediction of the GOCE in-flight performances on the measurement of the gravity gradient tensor and on the observables from which the precise orbit determination is performed. These performances are the result of factors that cannot be fully tested on ground (for the impossibility of reproducing the orbit gravitational environment) and can be treated analytically only in a simplified way (for their complexity), like the intrinsic noise of the gradiometer accelerometers, the behaviour of the Drag-Free and Attitude Control System of the platform, the functioning of the gradiometer in-flight calibration procedure. This paper presents the last prediction of the performances on the Level 1b product of the GOCE mission obtained from the E2E System Simulator.