The next generation of launch vehicles under development by NASA requires significant mass reduction to fully meet mission and performance needs. For example, NASA is aiming to create a new generation of heavy-lift launch vehicles to support both human spaceflight and space exploration missions. To ensure these vehicles can support all of the NASA needs, the mass of the propellant tanks must be significantly reduced, primarily through the use of composite materials. However, two primary challenges must be overcome to enable the use of composite tanks for these new classes of heavy launchers. One is to develop novel, microcrack-resistant, polymer matrix composite materials that will enable construction of 5 to 10 meter diameter composite tanks, and the second is to develop out-of-autoclave manufacturing methods that will enable the cost of these tanks to be 20-25% less than that of metal tanks. In the proposed program CTD plans to develop and evaluate new materials that will provide a strain to initiate microcracking that is 50% higher than that of the current materials. At the same time the materials will be optimized for out-of-autoclave processing of composite tanks. Of particular interest are low void content, long out-life, good tack properties, and out-of autoclave cure characteristics. The Phase I material development effort will explore several polymer chemistries including toughened epoxies, Polybenzoxazines and a hybridized version of the Polybenzoxazines and toughened epoxies. At the end of Phase I, CTD will fabricate and test a 15-cm-diameter by 18-cm-long, 1.9L cylindrical subscale tank to demonstrate the processing feasibility and performance of the new material.