NASA will try Discovery launch again on Saturday

Thick clouds over the launch site in central Florida forced the cancellation of Thursday’s scheduled launch of the space shuttle Discovery.

NASA flight controllers at Kennedy Space Center kept the crew strapped into their seats until the launch window officially closed at 9:36 p.m. EST in the hope that the weather might improve.

In the end, however, weather violated two flight regulations, one for the heavy clouds and a second one for the low cloud ceiling.

The regulations were adopted to allow safety systems on the ground to monitor the launch in case of problems.

The launch was delayed until Saturday at 8:47 p.m. EST.

The current launch window runs through about Dec. 26. The first 10 days of the window require a night launch.

The last three shuttle missions following the Columbia accident in 2003 were launched in daylight so that the cameras added after the disaster would have the best possible lighting conditions.

But because of NASA’s tight deadline to complete the International Space Station and retire the shuttles in 2010, it has become necessary to schedule night launches.

NASA said it feels comfortable resuming night flights because the success of the three post-Columbia flights has convinced managers that they understand and have mitigated the threat posed by foam insulation flaking off the external fuel tank -- the cause of Columbia’s loss.

Discovery’s 12-day flight will be one of the most complicated assembly missions to date. The crew led by commander Mark Polansky and pilot William Oefelein will attach a new strut section to the station and reconfigure the electrical and thermal control systems, which have been running off a temporary power grid for six years.

The last shuttle mission delivered a new set of solar power arrays that are designed to rotate so that they can always be pointed toward the sun.

This mission includes three spacewalks.

One of Discovery’s crew members, Sunita Williams, will remain on the space station as a replacement for Thomas Reiter, a European Space Agency astronaut who will return to Earth when Discovery completes its work.

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