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Extension of the Dynamic Abort Risk Evaluator (DARE) to Shuttle Derived Launch Vehicles (PSAM-0094)

Excerpt

The ability to successfully abort from a failing launch vehicle is a significant factor in crew safety. The Dynamic Abort Risk Evaluator (DARE) [1] developed by SAIC under the auspices of NASA's Space Shuttle Program has been an important model for assessing the effectiveness of aborts of the Space Shuttle during ascent. It has been used to identify the sources of greatest abort risk and perform trade studies among different abort options.

This paper discusses the application of the DARE methodology to Shuttle-derived launch vehicles (SDLVs) to produce a model that addresses the abort risk of the planned Crew Exploration Vehicle (CEV) from a failing SDLV during ascent. Shuttle-Derived Launch Vehicle DARE (SDLV DARE) models SDLV ascent aborts beginning with the initiating launch vehicle failure and ending at crew recovery. Unlike the Space Shuttle, which has potential abort initiators dominated by shutdown of a single Space Shuttle Main Engine (SSME), SDLVs are envisioned as providing abort capability as an integral dimension of crew safety, and are expected to be designed against a broad spectrum of mission-ending launch vehicle failures. For this reason, SDLV DARE has been developed with particular emphasis on identifying the risk-significant ascent failures that might occur, the opportunities for early failure detection and abort initiation, and the stresses produced by the accident environment upon the CEV as it separates from the launch vehicle and distances itself from the failure initiation and consequences.

The dynamic aspect of SDLV DARE is accomplished by Monte Carlo sampling of aleatory as well as epistemicuncertainty, using a nested loop approach. Failure distributions that would be constant using a conventional probabilistic risk assessment (PRA) approach can be dynamic within SDLV DARE; they can depend on user inputs (such as the time of the abort-initiating failure or the blast overpressure design limit of the CEV) and can be onditional on prior events. Additionally, unlike conventional PRA tools, where uncertainty can typically be applied only to basic event probabilities, in SDLV DARE uncertainty can be applied to any parameter, allowing uncertainties to be placed where they most naturally arise in the physics-based modeling of events, such as on positions, durations and stresses. The result is a rapid, integrated and flexible abort evaluation capability over a broad spectrum of system variations, performance characteristics and abort initial conditions.

SDLV DARE can provide valuable ascent abort insight throughout SDLV design, development and operational phases. It can be used initially during requirements development to determine how a high-level requirement flows down in terms of specific functional or system-level constraints. Another application during SDLV design is to support risk-informed system and operational trade studies, a role it can continue to perform over the life of the program, much as Shuttle DARE has done for the Space Shuttle. It can also be used to rank risks so that additional focus may be placed on the prevention or mitigation of risk significant scenarios, and it can be used to identify areas that have both high risk-significance and uncertainty thus warranting additional study. Finally, it can serve as an integration platform for ascent abort related information that is currently incomplete and, where present, scattered across the technical community.

  • Summary/Abstract
  • Introduction
  • Core Model
  • Treatment of Uncertainty
  • Tool Framework
  • Conclusions
  • References

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