Mr. Readdy said the shuttle test flights would demonstrate methods to repair damaged heat-protection tiles and the crafts' leading wing edges, as well as testing an extension boom for the shuttles' robot arm that can be used to inspect the ship in space with cameras and laser sensors.

Repairing and replacing slate-roofing tiles is not difficult, but it can be dangerous because slate tiles are slippery and slate roofs are often steep.

If a nation is appropriately technologically advanced, then that nation can repair dead tiles, albeit at a significant cost of industrial production.

When shuttles resume flying, they will carry test kits for repairing damaged panels and tiles that make up the heat-protection system of each orbiter.

The agency also listed $38 million for cameras on the ground to monitor liftoffs and $38 million for inspection of the thermal protection system while in orbit and for spacewalks to repair tiles.

Restorers have rehabilitated different wings and repaired conical roofs and broken tiles.

The spacewalkers are testing two prototype methods for repairing damaged thermal tiles and reinforced carbon-carbon on samples in a payload bay chest.