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NASA takes a composite approach to fuel tanks

By: PLASTICS & RUBBER WEEKLY

July 15, 2013

Successful tests of an all-composite cryogenic fuel tank for space vehicles hold promise for lower-cost access to space, perhaps before the decade is out, according to NASA.

The 2.4-meter diameter composite fuel tank, which was fabricated by Boeing Co. with funds from NASA's Space Technology Mission Directorate, contained 2,091 gallons of liquid hydrogen. The unit had to handle a series of shifts in its internal pressure and three temperature cycles ranging from ambient down to minus 423F.

The test at Marshall Space Flight Center paves the way for more tests next spring. These will subject a 5.5-metre tank to flight-comparable mechanical loads as well as temperature and pressure cycles. The unit is already in fabrication at the Boeing Advanced Development Centre in Tukwila, Wash.

Hopes are high that the project will achieve its goal of reducing the cost of building tanks by at least 25 percent from that of conventional aluminum-lithium tanks, while cutting the weight of tanks made from the lightweight aluminum alloy by at least 30 percent.

"This is a very difficult problem," says Mike Gazarik, associate administrator for space technology. "Composites and cryos don't work well together and these guys have done incredible work in figuring out how to design and how to fabricate these tanks."

"It performed nominally, and nominally is a very good thing for us," said John Vickers, project manager on the composite cryogenic tank technology demonstration project at Marshall.

Both test tanks are built up with thin-ply composites that do not require a pressurized autoclave for curing. The out-of-autoclave fabrication helps hold the cost down, says Dan Rivera, Boeing's project manager on the tanks, while the thin-ply approach, already in use on satellite structures and other Boeing products, prevents microcracking that causes leaks.