Tests have failed to find a way to stop these so-called "ice frost ramps" from falling off during launch.
"The decision was to fly these ice frost ramps as is, knowing that we can expect to have some small foam loss that could pose a risk," shuttle project manager Wayne Hale told a televised news conference.
Any breakaway pieces, however, are not expected to constitute a significant threat to the shuttle or it crew.
A trunk of insulation foam falling from fuel tank during Columbia's liftoff hit the shuttle's wing, leading to its disintegration during reentry into the earth's atmosphere in Feb. 2003. The incident had forced the shuttle fleet to be grounded and modifications of the fuel tank.
However, the foam problem emerged again during Discovery's launch in July 2005, the first shuttle flight since the Columbia tragedy, and forced a second redesign of the fuel tank, which removed two wedges of foam intended to shield cables and pressurization lines from buffeting winds during the shuttle's supersonic climb to orbit.
Hale described the change as the "largest aerodynamic change that we have made since the shuttle first flew."
"We're in a flight test program. When you make a major change, you should fly that major change and if you have to make additional changes then you make them after the flight," he added.
Additional work is planned to reshape the ice frost ramps upon Discovery's safe return, he said.
NASA plans 16 shuttle flights to complete the construction of the international space station and a possible maintenance flight to the Hubble Space Telescope. The shuttle fleet is expected to be retired by 2010.
hope it is a safe flight!
Space exploration is very important, because soon, very soon we'll start running out of raw materials on Earth and we'll turn to space for more resources.