Fast and Accurate Inflight Calculations of Electron Space Plasma Parameters

Abstract

Satellite and rocket borne experiments impose unique requirements on the systems that control them. High input data rates from sensors have to be coupled to a limited spacecraft telemetry resource. A suite of algorithms designed to ensure the most effective possible use of the telemetry allocation for an instrument studying space plasma electrons are described. These have been implemented in the data processing unit of the Plasma Electron and Current Experiment (PEACE) that will fly onboard the four Cluster spacecraft. Due to the high processing load and large throughput of data, two T222 17 MHz transputers were used as the onboard processors and the algorithms coded using the Occam programming language. To achieve the necessary reduction in the size of the dataset three different approaches have been used. Onboard moment calculations are performed. These provide a general characterisation of the measured electron distribution at the rate of once per spin of the spacecraft. For more detailed studies, sections and cuts of the raw sensor data can be selected. These distributions are designed to be compressed and telemetered at spin resolution. Some of these datasets can be aligned to the magnetic field direction. Finally much larger distributions of sensor counts can, for one spin, be stored and fed into the telemetry stream whenever there is room.