Application of Probabilistic Risk Assessment (PRA) During Conceptual Design for the NASA Orbital Space Plane (OSP)

Abstract

In order to meet the space transportation needs for a new century, America’s National Aeronautics and Space Administration (NASA) has implemented an Integrated Space Transportation Plan to produce safe, economical, and reliable access to space. One near term objective of this initiative is the design and development of a next-generation vehicle and launch system that will transport crew and cargo to and from the International Space Station (ISS), the Orbital Space Plane (OSP). The OSP system is composed of a manned launch vehicle by an existing Evolved Expendable Launch Vehicle (EELV). The OSP will provide emergency crew rescue from the ISS by 2008, and provide crew and limited cargo transfer to and from the ISS by 2012. A key requirement is for the OSP to be safer and more reliable than the Soyuz and Space Shuttle, which currently provide these capabilities.

NASA has taken an integrated systems approach in designing the OSP launch system and related ground operations and launch support services. This “System-Centric” approach, as opposed to a “Vehicle-Centric” approach, presents unique challenges in terms of meeting the desired safety and reliability requirements As a result, NASA is utilizing PRA, a methodology for quantitative risk assessment, on the entire system during the design process and throughout the life of the system. When PRA is performed early in the design and development cycle with full engineering design and operations involvement, the PRA based integrated system model will provide a means for methodical and objective optimisation of the conceptual design.

This paper discusses the development and implementation of PRA in the OSP Program. The OSP Program is the first major NASA program to perform and use PRA during the concept formulation phase of the program and is expected to produce the paradigm by which future space launch systems can be designed to meet successively higher safety and reliability demands [1].