The most drastic change to the space shuttle for the July 2006 mission is the removal of the Pal ramps from the external tank.

The two Pal [Protuberance Air Load] ramps acted as aerodynamic covers to the various cables and air lines running up the side of the tank. They were covered with insulating foam to prevent the formation of ice when it is filled with freezing liquid hydrogen fuel.

During Discovery's 2005 launch, a 0.5m long chunk of foam weighing about 450g broke away from one of the ramps on the external fuel tank.

Although it caused no damage, a similar foam-loss incident is believed to have directly caused the Columbia accident.

Following tests and analysis, engineers determined that removing the pal ramps would not affect the tank's aerodynamic behaviour and would reduce the threat to the shuttle from foam loss.

A camera was added to the external tank for the 2005 launch to monitor for foam loss during launch.