Space Processor Radiation Mitigation and Validation Techniques for an 1,800 MIPS Processor Board

R. Hillman, P. Layton, G. Williamson, L. Longden, C. Thibodeau, M. Conrad, and M. Giles
Maxwell Technologies

INTRODUCTION

As high-end computing and high reliability both become more of a necessity in space, there exists a large performance gap between what is available to satellite manufacturers and the current state of the commercial processor industry. The space community has been gravitating towards PowerPC™ microprocessors as a standard platform, mostly due to their excellent MIPS/watt performance and resulting lowered heat dissipation.

There is a recent trend for commercial PowerPC™ manufacturers, such as IBM and Motorola, to fabricate their next generation processors on smaller feature sizes and SOI (Silicon on Insulator) substrates. With radiation shielding and SOI fabrication processes, SEU’s (Single Event Upsets) and SET’s (Single Event Transients) are the dominant issue in using these advanced processors in space. IBM has recently come out with a high performance, very low power, SOI processor with some internal error correction.

Maxwell has integrated the latest technology processors, memory, and programmable logic coupled with the most advanced error detection and correction methods for the SCS750 (Supercomputer for Space 750).  Specifically, Maxwell has implemented Triple Modular Redundancy (TMR) for the 3 processors, Reed-Solomon Error Detection and Correction (EDAC) for the SDRAM and FLASH memory, modified hamming code EDAC for the EEPROM and radiation tolerant FPGAs from Actel to implement all of the board logic. This paper discusses the mitigation technologies chosen for each component type, the error correction capabilities, radiation test results of the processor and mitigation validation, and the SEU rate analysis for a geosynchronous orbit for the major components.

The SCS750 uses three IBM PPC750FX microprocessors, and is capable of executing more than 1,800 million instructions per second (MIPS). Three of these processors operating consume 4 times less power than a single "Rad-Hard" processor. This reduced power is mostly attributable to reduced feature size and a core voltage that can operate down as low as 1.2V, in addition to a much more efficient internal architecture. The SCS750 has computing performance of 90 MIPS/watt for the entire board, compared to approximately 20MIPS/watt for other leading edge rad-hard processor boards. The board can operate in a multitude of power modes. And, Maxwell’s architecture can use other PowerPC processors such as Motorola’s 7445 and 7455, which are also fabricated on SOI.