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"Making Safety Happen" Through Probabilistic Risk Assessment at NASANASA is using Probabilistic Risk Assessment (PRA) as one of the tools in its Safety & Mission Assurance (S&MA) tool belt to identify and quantify risks associated with human spaceflight. This paper discusses some of the challenges and benefits associated with developing and using PRA for NASA human space programs. Some programs have entered operation prior to developing a PRA, while some have implemented PRA from the start of the program. It has been observed that the earlier a design change is made in the concept or design phase, the less impact it has on cost and schedule. Not finding risks until the operation phase yields much costlier design changes and major delays, which can result in discussions of just accepting the risk. Risk contributors identified by PRA are not just associated with hardware failures. They include but are not limited to crew fatality due to medical causes, the environment the vehicle and crew are exposed to, the software being used, and the reliability of the crew performing required actions. Some programs have entered operation prior to developing a PRA, and while PRA can still provide a benefit for operations and future design trades, the benefit of implementing PRA from the start of the program provides the added benefit of informing design and reducing risk early in program development. Currently, NASA’s International Space Station (ISS) program is in its 20th year of on-orbit operations around the Earth and has several new programs in the design phase preparing to enter the operation phase all of which have active (or living) PRAs. These programs incorporate PRA as part of their Risk-Informed, Decision-Making (RIDM) process. For new NASA human spaceflight programs discussion begins with mission concept, establishing requirements, forming the PRA team, and continues through the design cycles into the operational phase. Several examples of PRA related applications and observed lessons are included.
Document ID
Document Type
Conference Paper
Boyer, Roger L.
(NASA Johnson Space Center Houston, TX, United States)
Hamlin, Teri L.
(NASA Johnson Space Center Houston, TX, United States)
Grant, Warren C.
(NASA Johnson Space Center Houston, TX, United States)
Stewart, Michael A.
(NASA Johnson Space Center Houston, TX, United States)
Cross, Robert B.
(NASA Johnson Space Center Houston, TX, United States)
Rogers, James H.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Berrios, Alfred S.
(NASA Kennedy Space Center Cocoa Beach, FL, United States)
Date Acquired
March 13, 2020
Publication Date
May 15, 2019
Subject Category
Astronautics (General)
Report/Patent Number
Meeting Information
Meeting: (International Association for Advancement of Space Safety) IAASS Conference
Location: El Segundo, CA
Country: United States
Start Date: May 15, 2019
End Date: May 17, 2019
Sponsors: International Space Safety Foundation
Distribution Limits
Work of the US Gov. Public Use Permitted.
Technical Review
Single Expert
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