Space Shuttle probabilistic risk assessment: methodology and application

Abstract

CONCLUSIONSOver the past four decades man has endeavored to explore the last frontier; to make space part of his habitable realm.Not unlike the expeditions of the oceans, this effort has resulted in some ofthe greatest moments in history, such as the moon landing, but unfortunately has been accompanied by tragic drawbacks, such as the Chulleizger accident.At the outset of all extraordinaryhuman adventures, when spirits are high and budgets are large, most drawbacks are seen as obstacles to be overcome rather than reasons to end exploration. However it is understood that with time the risk incurred and the monies expended should diminish to a level such that exploration gives way to transportation. The Space Shuttle is the embodiment of this transition in the modern age. However a s the technology needed for exploration has become more advanced so also must it become necessary to use more sophisticated methods for identifying and reducing risk to levels compatible with routine transportation.This paper describes the methodology and processes used for the probabilistic risk assessment of the Space Shuttle vehicle to systematically quantify the risk incurred during it nominal Shuttle mission and rank the risk driving coniponents to allow for a concerted risk and cost reduction effort. This year-long effort represents a development resulting from seven years of application of risk technology to the Space Shuttle. These applications were initiated by NASA shortly after the Challenger accident as recommended by the Rogers and Slay Commission reports. The current effort is the first integrated quantitative assessment of the risk ofthe loss of the shuttle vehicle from 3 seconds prior to liftoff to wheel-stop at mission end. The study which was conducted under the direction of NASA's Shuttle Safety and Mission Assurance ofice at Johnson Spaceflight Center focused on shuttle operational risk but included consideration of all the shuttle flight and test history since the beginning of the program through Mission 67 in July of 1994.The fundamental approach used in this assessment of shuttle operational risk is scenario-based and consists of quantitatively assessing the potential progression of postulated initiating events as intercepted and diverted by protective and mitigative features of the Shuttle system design. The approach implements a hierarchical model development methodolgy which has been found to ensure comprehensiveness and tractability by focusing the analysts' efforts on the main risk drivers. The models are qiiantifid by performing a data analysis effort in parallel with the model development. nit: risk ;issessment database includes all shuttle flight-relevant history, that is, precursors to flight fiiilure and test anomalies as well as actual in flight anomalies (IFAs).Both the models and database were recorded in a PC based application to facilitate the utilization and future modification of the Space Shuttle PRA.

Closed-Loop Thrust and Pressure Profile Throttling of a Nitrous-Oxide HTPB Hybrid Rocket Motor

“…1 NASA estimates that the Space Shuttle's liquid fueled main engines will fail catastrophically once every 1530 sorties per engine and its solid rocket boosters will fail catastrophically once every 1,550 sorties per motor. 2,3 While this level of risk is acceptable for experimental and government-operated vehicles, it is unacceptable for a potential commercial spaceflight operator.…”

Extended GTST‐MLD for Aerospace System Safety Analysis

“…The scenario begins with an “initiating event” that disturbs the system and culminates in an end state, i.e., consequence. Maggio ( 5 ) systematically presented the methodology and process used for the PRA of the space shuttle vehicle. In addition, some researchers have considered the organization safety risk in PRA; for example, Mohaghegh ( 6 ) extended PRA to include organizational factors in the framework socio‐technical risk analysis (SoTeRiA) for undertaking safety analysis.…”

Probabilistic Safety Assessment and Risk-Informed Decision-Making

“…However, following the Challenger explosion in 1986, probabilistic risk assessment at national aeronautics and space administration was revived, and the Columbia break-up in 2003 reiterated the need for risk analyses. National aeronautics and space administration used risk assessment and a combination of fault and event trees methods to model possible accident scenarios for the shuttle and International Space Station (ISS) programs (Maggio, 1996).…”