MCS. The high computational cost of a large number of MCS samples was alleviated by analysis RS, and numerical noise in the results of MCS was filtered out by design RS. RBDO of composite laminates is investigated for use in hydrogen tanks in cryogenic environments. The major challenge is to reduce the large residual strains developed due to thermal mismatch between matrix and fibers while maintaining the load carrying capacity. RBDO is performed to provide laminate designs, quantify the effects of uncertainties on the optimum weight, and identify those parameters that have the largest influence on optimum design. Studies of weight and reliability tradeoffs indicate that the most cost-effective measure for reducing weight and increasing reliability is quality control. A probabilistic sufficiency factor (PSF) approach was developed to improve the computational efficiency of RBDO, to design for low probability of failure, and to estimate the additional resources required to satisfy the reliability requirement. The PSF is a safety factor needed to meet the reliability target. The methodology is applied to the RBDO of composite stiffened panels for the fuel tank design of reusable launch vehicles. Examples are used to demonstrate the advantages of the PSF over other RBDO techniques