Satellite Onboard Data Reduction Using a Risc-V Core Inside an RTG4-Based Data Processing Pipeline

The Wide Field Imager (WFI) is one of two scientific instruments onboard the next generation European x-ray observatory ATHENA. It will orbit Lagrange point L2 and send the acquired science data to a single ground station with a downlink that is available for several hours once per day. The data rate of the downlink is a bottleneck, which limits the amount of science data that can be transferred. Measurement data of the eRosita satellite which is in operation since mid of 2019 shows that a high radiation background generates parasitic sensor data that adds to the science data. In order to remove the parasitic data from the science data stream onboard, a Risc-V softcore processor implementation in the RTG4 FGPA has been studied. Depending on the observation scenario, the data rate is reduced by a factor of more than 50. Within this article, we describe the WFI onboard processing architecture, the sensor effects on space radiation and the hard- and software architecture of the Risc-V softcore that can be implemented to reduce the data rate on board. Three test cases are defined and executed to verify the performance of the data reduction scheme.