will build two advanced composite cryotanks and test them with liquid hydrogen to see if they can improve the capability and cost of future launch vehicles.
Under a $24 millioncontract, the company will continue an earlier design effort by building a 10-meter-dia. cryotank and testing it at in Huntsville, Ala. ’s goals, according to Space Technology Program Director Michael Gazarik, are savings of 30% on weight and 25% on cost compared to aluminum tanks.
If the Boeing technology works out, it could solve a problem that effectively killed NASA’s X-33 reusable launch vehicle testbed. NASA canceled that program after spending almost $1 billion when a composite liquid hydrogen tank failed during loads testing at Marshall in November 1999.
A composite test tank filled with liquid hydrogen was able to handle simulated flight loads; but as it warmed, once the cryogenic fuel was drained out of it, the tank’s outer face sheet and core separated from the inner face sheet.
The failure was later attributed to microcracks in the inner and outer composite skins, which allowed pressurized hydrogen and chilled nitrogen gas from the tank’s safety containment to creep into the material and expand as it warmed.
For performance, the Boeing tank will use thin-ply composite materials already coupon-tested against microcracking.
“We use a thinner material than what we’ve used in the past. It’s a pretty deep physics-based mechanism that allows us to control and/or theoretically eliminate microcracking, and therefore eliminate permeability,” says John Vickers, manager of the National Center for Advanced Manufacturing at Marshall and project manager for the composite cryotank technologies and demonstration project. “It’s more layers, but thinner, and so this physics-based phenomenon is about the thinner material. The microcracks occur in the resin layers between the fiber layers, and by making the layer thinner, [we are] thereby eliminating the microcracks.”
For cost reduction, the tank uses the same type of polymer matrix composites that Boeing is using in its 787 structure.
But NASA is pushing beyond the manufacturing approach used in the 787 for deeper savings, using a technique NASA has worked with theand others to advance.
“Boeing uses an autoclave to cure their materials” for the 787, Vickers says. “We’re trying to use out-of-autoclave. That’s an even further push. That is truly, truly game-changing and would have effects throughout the industry. It takes a huge amount of cost.reported recently that 30% of the energy cost they had in producing composite structures was because of the autoclave.”
The weight and cost savings of the composite tankage could be attractive both in large launch vehicles and in orbiting fuel depots touted by the Augustine commission on the future of human spaceflight as an alternative to heavy-lift launchers.
NASA down-selected to Boeing based on Phase 1 work that also included ATK,and .