Preparations are on schedule for NASA's first night-time space shuttle launch in four years, managers said Wednesday.

The space agency plans to launch Discovery at 9:36 p.m. on Dec. 7. It will be the third launch of the year and the fourth since the Columbia disaster killed seven astronauts in 2003.

"There were really no dissenting opinions on the night launch," said Bill Gerstenmaier, NASA's associate administrator.

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NASA required the three launches after the Columbia accident to be in daylight so clear images could be taken of the space shuttle's external fuel tank in case foam fell off it. Foam breaking off the tank and striking Columbia's wing at liftoff caused the damage that led to the disaster.

The space agency needs to start launching shuttles at night to finish space-station construction by 2010, when the shuttle program ends. The external tanks had acceptable levels of foam loss during the last two liftoffs.

NASA managers also believe radar is sufficient to spot any pieces falling from Discovery's tank and that two in-flight inspections would detect any damage.

If the shuttle were damaged during liftoff, astronauts could seek shelter at the space station while awaiting a rescue flight.

If the launch does not happen on Dec. 7, NASA can keep trying through Dec. 17. After that, the agency will re-evaluate its options and may call it quits until January.

NASA wants Discovery back from its 12-day mission by New Year's Eve because shuttle computers are not designed to make the change from the 365th day of the old year to the first day of the new year while in flight.

The space agency has figured out a solution for the New Year's Day problem, but managers are reluctant to try it since it has not been thoroughly tested.