In space vehicles, size may not matter, but weight does. Hoisting a payload straight up to escape Earth's gravity requires a phenomenal expenditure of energy, and every ounce saved in either launch vehicle or payload weight translates to lower project costs. Lightweight and strong composite composite laminates at cryogenic temperatures. Microcracks can occur in any laminate because of the difference between the axial and transverse coefficients of thermal expansion (GTE) in each ply, explains Brian Wilson, president of Wilson Composite Technologies (Folsom, Calif.). "Transverse microcracks in the resin can be generated between the fibers as the laminate cools after cure, and as temperature is lowered to cryogenic levels." Even at moderate pressure, the composite's exposure to temperature extremes and repeated fill-and-drain cycles causes thermo-mechanical loading, which exacerbates cracking and leads to permeation leak paths, easily traversed by small hydrogen and oxygen molecules. The issue isn't helped by the fact that most thermoset systems lose strain capacity and become brittle at cryogenic temperatures. materials are already deployed in many applications, such as launch vehicle bodies, fairings and payload components. But tankage for super-cold liquid fuels - liquid hydrogen, liquid oxygen (LOX) and others - is still the purview of metals. Why? Despite years of testing, concerns still exist about the potential for leaks, due to microcracking of traditional carbon/epoxy
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