Defining radiation 'safe' zones for operating the High Rate Picture Transmission (HRPT) instrument onboard the Metop satellite

We describe analysis that identified sections of the Metop satellite orbit where the High Rate Picture Transmission (HRPT) subsystem could operate without being damaged by high energy particle radiation. The satellite operates in a low altitude (~850 km) polar orbit and provides meteorological and space radiation data. Data from the meteorological suite of instruments onboard was designed to be transmitted in real-time through the low and high rate picture transmission (LRPT and HRPT) subsystems for local weather forecasting purposes. The susceptibility of the LRPT and HRPT to radiation was not realized until the onorbit failure of the LRPT just 11 days after turn on and the HRPT-A after 6 months of operation. Activation of the HRPT-B was delayed until the cause of the previous failures could be determined. Careful laboratory analysis revealed that a component of the instruments was highly susceptible to particles with high linear energy transfer (LET). In an effort to save some of the instrument capability, engineers and scientists from Europe and the United States combined their knowledge of the instrument with their understanding of the space radiation environment to identify limited areas free of high particle radiation where the instrument could be used safely. Here we describe how we calculated anomaly rates for the specific components at risk by adapting the CREME96 model to handle Gallium Arsenide components rather than the standard silicon. Using the anomaly rates, new operational strategies were adopted and the HRPT-B has been in use since September 2008.