Development of an innovative, two-processor data processing unit for the magnetospheric imaging instrument onboard the Cassini mission to Saturn. I. Hardware architecture

This paper presents an innovative two-processor computer architecture, developed for the data processing unit (DPU) of the Magnetospheric IMaging Instrument (MIMI), on-board the Cassini spacecraft mission to Saturn. The main advantages of this architecture are its high performance and reliability, and its intelligence. The high performance is justified by the following: 1) optimum combination of two powerful Harris RTX 2010 processors; 2) adoption of two independent main bus structures used for the communication of the processors with the various instrument interfaces and subsystems; 3) adoption of two additional local buses on each processor board used to speed the on-board operations of the processors; 4) high speed interprocessor communication port. The high reliability is justified by the following: 1) simplicity of hardware/software structures; 2) fault tolerance capabilities; 3) capability for on-flight hardware/software reconfiguration by ground command. Moreover, the on-board intelligence is justified by the following: 1) sophisticated fault protection, data handling, and instrument control software; 2) intelligent interfaces [implemented using held programmable gate arrays (FPGAs)]; 3) capability for autonomous on-flight hardware/software reconfiguration in case of an unrecoverable failure in one processor. The advantages of this architecture make it the best choice for the DPU of the complex, sophisticated scientific MIMI instrument, compared to the traditional master-slave (low reliability-single point failure) and common shared bus (low performance, hardware and software complexity) architectures.