Launch vehicle debris models and crew vehicle ascent abort risk

Abstract

In the event of a launch vehicle failure during ascent, a manned space launch system requires an ascent launch abort system that will be able to separate the crew module from the launch vehicle and return the crew safely to earth. One measure of the effectiveness and reliability of the launch abort system is its ability to reduce the risk of loss of crew from the failure environments, such as blast overpressure and debris strikes from an exploding launch vehicle, resulting from the launch vehicle failure scenario. Physics-based models are used to assess the evolution of, and risks presented by, the failure environments. In the case of debris strikes, the probability of the crew module being hit by at least one piece of debris is computed by modeling the evolution of the debris field over time and determining its relative position to the crew module. The characteristics of the debris field, including the number of pieces, the mass and reference area of each piece, the imparted velocity magnitude and direction and the ballistic coefficient, are defined by a debris catalog. A model has been created to generate a debris catalog using a combination of empirical- and physics-based models. The debris catalog model accounts for design features of the launch vehicle and the failure mechanisms involved in determining the number of pieces and imparted velocity. The model results are compared with a published catalog for the Space Shuttle external tank. The sensitivity of the risk prediction to the number of pieces and the imparted velocities are studied. The debris catalog generation model provides an additional tool in the risk assessment of ascent aborts for manned launch systems.