PREPARATORY RADIATION MONITORING ACTIVITIES FOR THE GALILEO PROGRAMME

摘要

Spacecraft in the planned Galileo navigation system will be flying in the most severe near-Earth radiation environment, in the heart of the outer electron belt. This environment is both highly variable and relatively poorly characterised. Since the Galileo system is based on non-military standards, special care needs to be taken from the outset to provide capabilities for monitoring the ambient radiation fluxes, as well as for analysing their possible effects on sensitive onboard systems.rnFor the initial stage of Galileo, the Galileo System Test Bed (GSTB), two test spacecraft are being built. As one of the tasks of this initial phase is in-orbit environment characterisation, both of the test spacecraft are equipped with radiation monitoring equipment. The first spacecraft, GSTB-V2a, will carry two radiation monitoring payloads: The MERLIN instrument by QinetiQ, comprising of improved versions of the previously flown CREDO and SURF experiments, and the CEDEX instrument by the University of Surrey - Surrey Satellite Technology Ltd. (SSTL), also based on previously flight-proven instruments, the CREs. In the second spacecraft, GSTB-V2b, the ESA Standard Radiation Environment Monitor (SREM), flying already on various ESA missions, will be included. The main characteristics and expected data output of these three instruments are described.rnTo support the actual radiation monitoring, special care also needs to be taken also with instrument calibration, simulation, and data analysis activities. Various developments are underway for joint calibration activities; for simulation of the instrument response in a common (GEANT4) software framework; and for the development of ground-based space environment support systems to aid the Galileo system operators. The status of these various support activities will be described. Finally, the outlook and recommendations for radiation monitoring activities concerning the final Galileo system will be given.