CAPE CANAVERAL - NASA's shuttles are free to resume night launches.

Senior managers decided late this week to evaluate daytime or nighttime launch requirements on a mission-by-mission basis based on the kind of pictures and video its engineers need of the shuttle and its external tank during the first minutes of flight.

For NASA, the decision gives managers the flexibility they need to fly 15 or so more missions necessary to finish building the International Space Station by 2010.

For the rest of us, the change offers a chance to once again witness the unique spectacle of a nighttime shuttle launch turning darkness to daylight along the Space Coast.

The first night launch will be the next shuttle mission, set to blast off at 9:38 p.m. on Dec. 7. Kennedy Space Center launch crews remain on track to make that target.

Launching at night poses no threat to the safety of the shuttle or its astronaut crews, according to an agency document summarizing the decision.

NASA imposed daylight launch restrictions after the 2003 Columbia catastrophe.

The goal was to get clear photographs and video of the launching shuttle and of the external tank as it falls away from the orbiter in space. Engineers needed the images to help determine if changes made to the external tank stopped its foam insulation from peeling off in flight and smashing into the orbiter, the long-neglected problem that was blamed for the loss of Columbia and seven astronauts.

NASA always planned to lift the restriction after two flights.

Instead, it took three flights for the agency to gain confidence that the tank foam will no longer come off in large enough chunks to damage the shuttle's heat-shielding.

Once Atlantis landed safely, NASA managers said they were confident they would be able to eliminate the daylight launch restrictions.

However, managers waited for experts to analyze all of the available data before making an official decision.

The restrictions not only required the shuttle to launch during daylight on the ground at KSC, but at times when the external tank [image] would be illuminated by the sun as the orbiter dropped it in space.

That way, astronaut photographers and digital cameras mounted in the spaceship's belly could snap pictures to see if any big pieces of foam were missing.

The requirement created short windows several times a year when a shuttle could launch and meet the rules.

Being able to launch at night makes most days of the year available.

NASA will look at missions individually and could impose the restriction on particular flights if there is a specific need for certain kinds of launch imagery.

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