CAPE CANAVERAL, Fla., Nov 7 (Reuters) NASA cleared space shuttle Discovery to return to Earth following a successful 15-day mission that laid the groundwork for the arrival of new laboratories at the International Space Station.
Subject to good weather, Discovery will leave orbit and plow through the atmosphere before touching down at the Kennedy Space Center in Florida at 1:02 p.m. EST (1802 GMT) today.
The atmospheric re-entry will be the first that will take the plummeting shuttle over populated land areas in the United States since the 2003 Columbia accident.
NASA shifted the astronauts' schedule to accommodate a day-time landing instead of a night-time one, setting the spacecraft up to be visible to shuttle-watchers on the ground.
''It's worth looking out for,'' flight director Bryan Lunney said yesterday.
For the first landing opportunity today, Discovery would follow a track over Montana, central Nebraska, northeast Arkansas, Alabama and northern Florida before reaching central Florida's east coast where the shuttle's home port is located.
Columbia, which unbeknown to its crew had a hole in its heat shield, disintegrated while returning to Florida, scattering thousands of pieces on Texas and Louisiana.
The seven astronauts on board were killed and NASA grounded shuttle flights for 2 1/2 years while the accident was investigated.
Ever since, the US space agency has brought shuttles in over water in the later stages of their descent. It also has checked shuttle heat shields with a laser-tipped robot arm before they return to Earth.
NASA officials said no major damage had been found on Discovery.
During an in-flight interview, Discovery commander Pamela Melroy, who will be landing the spaceship for the first time, said she preferred landing by daylight.
''I think it's a little easier but the real reason we asked for the switch is because the sleep shift involved shifting later instead of earlier (which is) a lot easier to do physiologically.'' NEW VESTIBULE Melroy and her crewmates spent 11 days at the station to install the Italian-built Harmony vestibule, which gave the outpost its first new room in six years. Astronauts also relocated an 18-tonne solar power panel truss to make way for station expansion.
The 110-foot-long (33 metre) solar panel tore in two places as it was being unfurled in its new home, forcing NASA to send an astronaut out on a risky space walk to repair it.
Had a repair proven impossible, plans to expand the half-built 0 billion space station would have been in jeopardy due to power and stability problems.
The work, however, put added pressure on NASA in its quest to deliver Europe's long-delayed Columbus laboratory module to the station next month.
One of five spacewalks planned during Discovery's stay was postponed until after the shuttle's departure and the crew of the space station will be hard-pressed to finish getting everything ready for Columbus' planned December 8 arrival.
NASA has a small window up to December 13 to launch its next shuttle mission after which the sun would create unacceptable temperatures for the shuttle to be docked at the outpost.
The US space agency plans 11 more construction missions and two resupply flights to complete the space station by the time the shuttles are retired in 2010.
A final servicing call to the Hubble Space Telescope in September is also on the schedule.
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