Discovery (file photo)

Top officials at the U.S. space agency, NASA, say they have begun their final countdown for a launch of the space shuttle Discovery on Wednesday. NASA officials say a plastic cover fell off a window of the shuttle late Tuesday, causing minor damage but they do not anticipate the incident will cause any launch delays.

 NASA officials say there is a 60 percent probability of Discovery lifting off during the shuttle's 10-minute launch window.

All eyes are on the weather at the Kennedy Space Center in Florida. NASA plans to launch Discovery on Wednesday afternoon in Florida. However, if there is heavy rain within 20 nautical miles or 37 kilometers, of the launch pad, NASA will delay the launch for at least a day.

NASA engineers have spent by some estimates over one billion dollars to re-tool the shuttle following the catastrophic disintegration of the shuttle Columbia, on February 1st, 2003. NASA's administrator, Michael Griffin, says it is time for NASA to return to manned spaceflight.

"That we have come through a very difficult period at NASA and in our progress toward developing human spaceflight and that we are back on line and ready to go," he said.

NASA will have over 100 cameras positioned around Cape Canaveral to observe the launch. Columbia's mission was doomed at launch when about a three-kilo piece of insulation broke off the shuttle's external fuel tank and caused a crack in Columbia's left wing, allowing hot gases to enter the shuttle on re-entry and destroy the craft.

NASA has redesigned many aspects of the shuttle and changed many launch procedures to ensure a safe flight, but administrator Griffin says everyone should recognize that space flight is inherently dangerous.

"In the course of trying to conduct space flight activities we in the United States have lost three crews," Mr. Griffin said. "Russia has lost two. It is a dangerous business and it will be for the foreseeable future. We will try every time to make it less dangerous than the time before, every time to make it more reliable than the time before."

Retired Air Force Colonel Eileen Collins will pilot Discovery to a docking with the international space station during the shuttle's 13-day mission.

Unlike previous shuttle flights, Discovery's mission and the next shuttle flight of Atlantis will not carry out extensive scientific experiments. NASA administrators say the two missions are essentially test flights to evaluate changes made to the shuttle program since the Columbia disaster.