Assuring fault tolerance of the Soyuz MS manned transport spacecraft

The paper is devoted to assuring a failure-free operation of the Soyuz MS manned transport spacecraft and the safety of its crew and also to making an analysis of the validity of fault tolerance requirements specified for the spacecraft in the scope of its participation in the International Space Station (ISS) activities. The analysis of methods and the results of work to assure resistance to failures of the Soyuz spacecraft in the development and the subsequent modernization phases are presented. The concept of requirements for fault tolerance adopted in the design and development of the Soyuz MS spacecraft is stated, modifications made onboard the spacecraft to fulfill these requirements are described. Objectives of the ground development test and the plant check-out tests to present failures in the flight of spacecraft are reviewed. An approach to statistical analysis of comments and failures detected during the flight of the spacecraft is proposed; it allows to give an independent assessment of the efficiency of tests to prevent failures in flight. The results of statistical analyses of comments and failures recorded in flights of the Soyuz spacecraft to the ISS (a total of 55 spacecraft) are presented. Based on the results a conclusion about the validity and sufficiency of requirements for fault tolerance is made.