1991-07-01

Impact of Fault Tolerance Requirement for the European EVA System 911581

A European Extra-Vehicular Activity (EVA) System is being developed by the European Space Agency (ESA) as part of its Hermes Programme, with the primary objective of providing a manned intervention capability for external servicing of the Columbus Free Flying Laboratory. The development phase started in 1988.
A major design driver for the EVA system is the required level of failure tolerance, to ensure the achievement of sortie objectives and crew safety. The failure tolerance requirements placed on the EVA system may be summarised as follows: no single failure should result in sortie abort, and a safe return to the Hermes “safe-haven” should be possible following a second failure.
This paper presents possible design solutions to this requirement, in particular for life support and associated functions. The failure tolerance characteristics of existing American and Russian EVA systems are also examined for comparison. Although they were developed to satisfy similar failure tolerance requirements, differences in mission requirements, operational environment and development philosophy have resulted in differences in the implementation of failure tolerance.
In this analysis, the relevant results of system engineering and technology development work during the initial phases of the European EVA System development are taken into account.

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