The Implementation of Data Compression in the Cassini RPWS Dedicated Compression Processor

Abstract

The Radio and Plasma Wave Science instrument is a part of the scientific payload of the NASA/ESA Cassini mission that is due to be launched to study the planet Saturn in 1997. Such instruments are capable of generating vastly more data than the data systems of the spacecraft and the link to the Earth can handle and so data selection and data compression are important. Within RF'WS some data compression is performed in a dedicated compression processor, DCP. This processor is based on an HS-80C85 processor and includes several algorithms which have been tested for their efficacy in the compression of plasma wave data. Criteria have been derived for the acceptable data distortion that will not adversely affect the scientific value of the data. The main algorithms that are installed in the DCP are the Rice algorithm and a Walsh transform. These are complemented with simple bit stripping and packing algorithms. The hardware of the DCP is described. A discussion of the software structure is given together with performance statistics on the software as implemented in the engineering model, of RF'WS. The software structure in the DCP makes it a suitable host for further scientific software. One such is an algorithm to detect dust impacts and this wdl also be installed in the engineering model.