This paper describes the development of methods to determine allowable hydrogen permeation rates for composite cryogenic tanks for launch vehicles. Background information on the development of hydrogen permeation testing is provided and permeation testing apparatus developed recently is described. Calculated results for a variety of tank designs and permeation failure modes are included. Tank designs are considered for both reusable and expendable launch vehicles. Failure modes related to system performance and to specific design features are addressed. A comparison of the calculated allowable permeation rates is made to recent permeation test data obtained on the NASA Space Launch Initiative program.
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