MODELING COMMON CAUSE FAILURES OF THRUSTERS ON THE INTERNATIONAL SPACE STATION (ISS) VISITING VEHICLES

摘要

This paper discusses the methodology used to model common cause failures of thrusters on the International Space Station (ISS) Visiting Vehicles. The ISS Visiting Vehicles each have as many as 32 thrusters, whose redundancy and similar design make them susceptible to common cause failures. The Global Alpha Model (as described in NUREG/CR-5485) can be used to represent the system common cause contribution, but NUREG/CR-5496 supplies global alpha parameters for groups only up to size six. Because of the large number of redundant thrusters on each vehicle, regression is used to determine parameter values for groups of size larger than six. An additional challenge is that Visiting Vehicle thruster failures must occur in specific combinations in order to fail the propulsion system; not all failure groups of a certain size are critical. Note that the example illustrated in this paper is not specific to an existing propulsion system and is intended to explain general methodology without disclosing vehicle-specific details. An earlier version of this paper was published June 22, 2014 by Probabilistic Safety Assessment and Management Conference (PSAM) 2014 (Ref. 1).