Tank testing for Discovery

The external fuel tank that will help launch the space shuttle Discovery on its next mission arrived two weeks ago at NASA's Kennedy Space Centre.

Designated ET-119, the tank will eventually be mated to the twin white solid rocket boosters and the orbiter Discovery.

anticipates launching the Discovery mission STS-121 in May. But the agency is still working to verify that changes to the design of the shuttle's external tank will result in a safer launch. Upcoming wind tunnel tests are expected to offer important engineering data that will help determine the feasibility of a May launch.

'The thing that is going to speed up getting Discovery off the ground is not work at Kennedy,' space shuttle programme manager Wayne Hale said, 'but the engineering analysis and tests that go toward proving that this launch vehicle is safe to fly.'

In Iowa Joe Gray, leader of the X-ray research group at Iowa State University's Centre for Nondestructive Evaluation, is studying how X-ray backscatter imaging and computer simulation modelling can help NASA look through the spray-on foam that insulates and protects the shuttle's external fuel tank.

Unlike traditional X-rays that make images by transmitting radiation through an object to a detector, backscatter technology creates images based on the electromagnetic radiation deflected by objects back to a detector.

Pieces of the foam fell from the shuttle Columbia during its January 2003 launch, damaging the spacecraft's left wing and causing the shuttle to break apart when it re-entered the Earth's atmosphere, killing the crew.

When the first shuttle flight since the Columbia accident launched in July, more foam chunks fell from Discovery's external fuel tank and sent engineers looking for more answers.

NASA is asking Gray and his research team to do an $88,000 (£51,000) three-month study to answer two questions about NASA's foam testing. Gray said engineers want to know more about the ability of X-ray technology to detect bubbles when layers of shuttle foam curve around corners; and about the technology's ability to see any bubbles near the foam's layer lines.

The Iowa State researchers are taking X-ray images of foam samples and loading that information into a computer simulation program. They are running computer simulations that model the X-ray technology's ability to find defects in the foam.

Gray said he expects to send NASA a final report on the research this month.