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The Atlantis astronauts tested the shuttle's re-entry systems early Thursday and began packing for landing Friday, weather permitting, to close out a successful mission to overhaul the Hubble Space Telescope. The flight plan calls for a de-orbit rocket firing at 8:49:16 a.m. Friday, setting up a landing on runway 15 at the Kennedy Space Center at 10:00:31 a.m. A second landing opportunity is available one orbit later, at 11:39:18 a.m.

With no major technical problems in orbit, the only question mark is the weather, with forecasters predicting a broken cloud deck at 4,000 feet, crosswinds above 15 knots and a chance of thundershowers within 30 nautical miles of the runway, all violations of NASA's landing weather flight rules.

High winds and torrential rains rumbled through the area overnight as severe thunderstorms lashed Florida's Space Coast. There is a 50 percent chance of heavy rain, high winds and thundershowers all day Thursday and more of the same expected overnight and Friday.

But the astronauts have conserved power and now have saved enough hydrogen and oxygen to power the ship's electricity producing fuel cells through Monday. As a result, NASA is not staffing backup landing sites Friday. If the weather or some other issue blocks the two available landing opportunities, the crew will stay in orbit an extra day and try again Saturday.