Risk vs Return: Mitigating an Onboard Radiation Failure Susceptibility

As part of the EUMETSAT-NOAA cooperative Initial Joint Polar System, MetOp performs an operational Earth observation mission for meteorological purposes from a highinclination Low Earth Orbit. MetOp-A is the first satellite of a series of 3. Two subsystems perform a direct broadcast service for local and regional data users: the Low Rate Picture Transmission (LRPT) and the Advanced High Rate Picture Transmission (A-HRPT). After the launch of MetOp-A on 19 October 2006, the LRPT subsystem failed after just 11 days. The A-HRPT failed after 6 months of operations. The EUMETSAT led Anomaly Review Board performed a failure analysis including several in-orbit tests. EUMETSAT established that the failed component was most likely to be a transistor unit in the output stage of the Solid State Power Amplifier inside the A-HRPT. Having procured the satellite for EUMETSAT, a subsequent ESA led Failure Investigation Board concluded that the failure on the transistor was due to a Single Event Effect from a heavy ion impact. EUMETSAT took the decision to investigate how to resume a restricted, regional A-HRPT service with a compromise between risk and user return. The modeling of the Space Environment addressed the global variations in heavy ion and plasma (proton) fluxes at the MetOp altitude and associated failure rates to the MetOp sensitive component. Other agencies and institutions were consulted and finally a failure rate model for the GaAs transistor technology was obtained with active support from NOAA/SWPC. This model allows the instantaneous transistor failure probability to be calculated. Added with a positive outcome concerning the hardware switching qualification limits, a new concept for fulfilling the needs of the local and regional data user community was derived and implemented in the ground segment. The A-HRPT operations were resumed in September 2008. After this first reactivation of A-HRPT, and given the high interest of end-user community, the coverage has been extended and will be reviewed for future potential incremental additions.