Configurable fault-tolerant processor (CFTP) for spacecraft onboard processing

Abstract

The harsh radiation environment of space, the propensity for SEUs to perturb the operations of silicon-based electronics, the rapid development of microprocessor capabilities and hence software applications, and the high cost (dollars and time) to develop and prove a system, require flexible, reliable, low cost, rapidly developed system solutions. A reconfigurable triple-modular-redundant (TMR) system-on-a-chip (SOC) utilizing field-programmable gate arrays (FPGAs) provides a practical solution for space-based systems. The configurable fault-tolerant processor (CFTP) is such a system, designed specifically for the purpose of testing and evaluating, on orbit, both the reliability of instantiated TMR soft-core microprocessors, the ability to reconfigure the system to support any onboard processor function, and the means for detecting and correcting SEU-induced configuration faults. The CFTP utilizes commercial off-the-shelf (COTS) technology to investigate a low-cost, flexible alternative to processor hardware architecture, with a total-ionizing-dose (TID) tolerant FPGA as the basis for a SOC. The flexibility of a configurable processor, based on FPGA technology, enables on-orbit upgrades, reconfigurations, and modifications to the soft-core architecture in order to support dynamic mission requirements. Single event upsets (SEU) to the data stored in the FPGA-based soft-core processors are detected and corrected by the TMR architecture. SEUs affecting the FPGA configuration itself are corrected by background scrubbing of the configuration. The CFTP payload consists of a printed circuit board (PCB) of 5.3 inches/spl times/7.3 inches utilizing a slightly modified PC/104 bus interface. The initial FPGA configuration is an instantiation of a TMR processor, with included error detection and correction (EDAC) and memory controller circuitry. The PCB is designed with requisite supporting circuitry including a configuration controller FPGA, SDRAM, and flash memory in order to allow the greatest variety of possible configurations. The CFTP is currently manifested as a space test program (STP) experimental payload on the Naval Postgraduate School's NPSAT1 and the United States Naval Academy's MidSTAR-1 satellites, which was launched into low earth orbit in March 2003.