Use of probabilistic risk assessments for the space station program

The purpose of risk management is to identify what can go wrong, how likely it is for these to occur, and what are the consequences if they were to occur. The International Space Station (ISS) Program office uses a continuous risk management process in identifying, analyzing, planning, tracking, controlling and communicating risks. This strategy manages risk by: (i) embedding risk management processes into normal day-today activities to identify and help manage any risks or potential threats; (ii) facilitating risk-management processes and analyses by providing analytical support and tools. One of the key quantitative risk analysis methods employed by the ISS program is the probabilistic risk assessment (PRA) modeling techniques. PRA is a comprehensive, structured and logical analysis method for identifying and assessing risks in complex technological systems for the purpose of cost-effectively improving their safety and performance. The International Space Station has been modeled using this PRA methodology and is now used extensively by program management to make strategic decisions. The PRA results can be used as a powerful decision-making tool in support of design, operations, and prioritizing upgrade or reconfiguration decisions. The process helps identify potential new risks, analyze existing risks and subsequently can weigh different options available to the Program to mitigate those risks. The ISS PRA captures possible accident scenarios that lead to several undesired consequences called End States. Some background into the PRA methodology including examples of trade studies recently conducted for the ISS Program will be highlighted in this paper.