Reliability Case Notes No. 6. Risk assessment of the Ellsworth probe: development, design and deployment

Abstract

The Natural Environment Research Council is partly funding the development and deployment of a scientific probe in the Antarctic subglacial Lake Ellsworth. The deployment will take place in 2013.

This report aims to quantify the technical risks of the probe development, design and deployment. A high level representation of the entire probe deployment process is captured in a Markov chain – a form of graphical probabilistic model. The transition from one state, or phase of the deployment, to the next depends on several factors, including: reliability of components and reliability of processes. We use fault trees to quantify the probability of failure of the complex processes that must take place to facilitate the transition from one state to another. The Shelf expert judgment elicitation package was followed to elicit expert judgments for the probability of failure for each failure mode.

The top two technical risks are:
• Failure to clean Jacket of the hot water drill hose: 95% quantile at 0.96.
• Probe electronic failure: 95% quantile at 0.11. Here, the top failure mode is optical connector failure.

The Markov chain was used to estimate the availability of the probe from different phases of the
deployment.
• From on-site probe cleaning: 95% confidence that the probability of success is higher than 0.7.
• From on-site testing: 95% confidence that the probability of success is higher than 0.73.
• From sheave deployment: 95% confidence that the probability of success if higher than 0.83.
• From probe positioning: 95% confidence that the probability of success is higher than 0.90.

Finally, the probability of a successful probe deployment following the probe pre-deployment is
greater than 0.87, with 95% confidence.

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Identifiers

ORCID for M.P. Brito: orcid.org/0000-0002-1779-4535

ORCID for M. Mowlem: orcid.org/0000-0001-7613-6121

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