Reliability analysis of external tank attach ring (ETA)

The authors deal with reliability analysis of the external tank attachment ring used as an interface between the external tank attach struts and solid rocket motor. It is part of the solid rocket booster and is a critical element of the Shuttle and hence, was chosen for the reliability study. The approach used here is to treat the material, geometric and load properties as probabilistic and use the corresponding deterministic functional relations for calculation of normal, shearing and principal stresses. No new finite element analysis calculations are made but the existing results for membrane and grid forces are utilized in the reliability calculations incorporating the uncertainty of these variables based on the existing data in the literature and past experience at NASA. The final comparison is made between the results of reliability analysis and the corresponding deterministic analysis in terms of probabilistic safety margin values