The U.S. space agency NASA has completed its initial safety modifications to the space shuttle's external fuel tank and wants to see how it flies before making any more. A flight test is planned for July, the first shuttle mission in one year.
NASA has spent hundreds of millions of dollars redesigning the exterior layer of hard foam insulating the giant orange fuel tank that launches side by side with each shuttle, feeding its enormous appetite for liquid hydrogen and oxygen on its way to orbit.
The space agency wants to prevent a recurrence of shedding foam that punched a hole in the wing of the shuttle Columbia in 2003, causing it to burn up upon re-entry, killing seven astronauts.
NASA has removed the foam from the tank site that contributed that deadly debris and reshaped it in other places. The attempt has been to minimize the amount that breaks away during the tremendous physical stresses of launch.
The agency's chief of space operations, Bill Gerstenmaier, says NASA wind tunnels are limited in their ability to simulate these forces, so the only thing to do now is to subject the redesigned tank foam to real launch conditions.
"We're really pushing the state of the art of our analysis in wind tunnel capabilities, so at some point, you really need to go to flight, and you need to go to flight with some instrumentation so you can monitor that performance and see how the design you have put together with the best of your engineering capabilities actually performs in flight," he said.
NASA found during last July's mission of the shuttle Discovery, the first since Columbia's demise two-and-a-half years earlier, that foam shedding was still a problem. So it imposed a second flight moratorium and went back to work on the fuel tank's foam design.
The agency plans to lift that flight ban in July and send Discovery to the International Space Station.
The chief of shuttle operations, Wayne Hale, says flying without further planned modifications presents some risks. But he says the existing changes have altered the fuel tank's aerodynamics and NASA wants to see how the unit acts before making any more alterations.
"There was a strong, concerted opinion from several folks that we should wait until we have a good design on these pieces of foam and then change them as well before we go fly," said Mr. Hale. "However, at the end of the day, we came back to the fact that it is appropriate to make one change at a time to take care of the biggest problem that we have, and then work our way to the next situation that we would like to improve."
Hale says the decision was not driven by pressures to return shuttles to flight to complete space station construction.
Discovery's next mission will bring fresh supplies to the outpost and a third crewmember. He is German astronaut Thomas Reiter, the first non-American or non-Russian long-duration crewmember on the station. It has been operating with only two astronauts since the Columbia accident because Russian cargo rockets do not have enough volume to carry goods for more.
NASA plans a second shuttle mission later in the year to test any further fuel tank modifications.