Risk assessment of wire failures causing uncommanded orbiter RCS firing while docked at the ISS

NASA is currently implementing a plan to return the space shuttle orbiter to a safe flight status. One 'return to flight' technical issue is the potential hazard of an uncommanded reaction control system (RCS) firing while the Orbiter is docked at the International Space Station (ISS). This paper shows two different quantifications of the probability of an uncommanded RCS firing. The fault tree based methodology is based on known failure modes and from operational considerations that potentially can lead to damage. The results of this study aided in the management of 'return to flight' risk by helping prioritize proposed RCS wiring upgrades with respect to other 'return to flight' safety issues.