Reliability of benthic stations: The NADIA II example

NADIA II, the logging shuttle, was first designed for the re-entry of deep sea Ocean Drilling Program (ODP) boreholes. It is deployed and controlled by the 6000 m manned submersible NAUTILE. It was used as a deep sea observatory for seismic long term measurements. During construction, the rules of safety for the operation with manned submersibles were observed for this NAUTILE tool, to finally obtain a device capable of satisfactory use during a scientific cruise with multiple dives on several boreholes. A dependability analysis has been performed on NADIA II. It shows that for long term measurements, a precise analysis of functions and components and complete qualification are needed. As in space satellites, the deep sea instrumentation for long term observations needs reliability. Industrial methods and adapted design tools will be of great help for reliability evaluation of this new kind of equipment