Composite cryogenic tank under development

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Mojave, California-based reusable rocket-powered vehicle developer XCor Aerospace is to build a demonstration composite cryogenic tank under a four-year $7 million NASA exploration systems research and technology contract.

The advantage of composite materials is that their thermal stability allows a tank to be part of the vehicle's structure, which saves weight. Normally fuel tanks have to be separate and suspended within the vehicle's structure. The Xcor Aerospace tank would hold liquid oxygen and is to be constructed with a type of fibre and fluoro polymer that the company is currently patenting.

The company claims that its technology has the ability to retain its strength and flexibility at cryogenic temperatures and that its fluoro polymer is not flammable. Brittleness and flammability are said by XCor have been issues with previous composite tanks' materials.

"We are taking a different approach. Everyone thinks of the X-33 tank, but that tank failed for well-understood reasons," says XCor Aerospace president Jeff Greason. The Lockheed Martin X-33 reusable launch vehicle tank demonstrator failed in November 1999 when micro cracking occurred in the tank wall.

Greason's company has been given $1 million for its tank design for the first year, but must meet targets to continue the work beyond that. Greason has competition as Northrop Grumman successfully tested a composite tank developed for $30 million from 2001 to 2004. It was repeatedly fuelled and underwent simulated launch stresses.

ROB COPPINGER/COLORADO SPRINGS