DMS-R 20 years of fault tolerant computer operation on ISS-continuous sustaining maintenance and overcome of obsolescence issues-

摘要

Nearly twenty years ago Zwezda (3Be3a) equipped with the DMS-R Fault tolerant computing (FTC) system - a configuration of three identical fault containment regions (FCR) designed at Airbus DS Bremen- started its operational life in space. DMS-R, the Data Management System Russia is the fault tolerant computing system responsible for the altitude regulation of the ISS as well as for the control of the life support system. The system was designed to guarantee 15 years of life time in space by exchange on box level (FCR) including the number of spares produced. The DMS-R FTC computing system has now been operating for nearly 20 years without serious problems on the ISS. However, the specified operational life time has already been passed. In 2014 a serious analysis of the occurred failure types and rates took place with the result that a high number of failure occurrences could be traced back to the work memory (RAM) of the processor board. RSC-E, ROSCOSMOS and ESA envisaged the need for additional computer spares being available to serve for ISS lifetime extension until 2020. Due to obsolescence of EEE parts a simple re-manufacturing was not possible. This was the trigger to think about alternative design approaches from board level up to new computer architecture on box level. Due to cost constraints a processor board alternative based on interface and SW compatibility to the largest extend possible was designed and implemented. The operational drawback to have an on-board ISS board level exchange to be performed by an ISS crew member had to be taken into account from the beginning.