NASA managers offered a generally upbeat appraisal of the launch prospects after a meeting Monday afternoon at Kennedy Space Center.
Weather has been a prime concern since Hurricane Dennis swept into Florida over the weekend. Ultimately, Dennis turned west, leaving Kennedy Space Center along Florida's Atlantic coast under mostly clearing skies.
Now the principal worry is the possibility of thunderstorms. Lt. Mindy Chavez of the Air Force's 45th Weather Squadron said there was a 70% chance that the weather will cooperate with NASA's launch day plans. Later in the week, predictions are for worsening conditions.
Even if the weather cooperates, a few late technical problems could delay the launch, NASA managers said.
Some officials have raised concerns about corrosion in fittings on the umbilical hoses that supply fuel and electricity to the shuttle. On Monday, it was revealed that recent tests showed that the skin of the shuttle might gain too much heat as it accelerates through the upper atmosphere to its final speed of 17,500 mph.
Managers seemed confident that the problems could be cleared by launch day.
But Wayne Hale, deputy manager of the shuttle program, said, "If we don't pass the certification requirements for launch, we don't launch."
NASA has said it has become much more safety conscious since the loss of Columbia, which broke up during reentry on Feb. 1, 2003. It turned out that a piece of lightweight insulating foam fell off the shuttle's external tank and tore a hole in the left wing on launch.
Discovery's 13-day mission will take it to the International Space Station, where it will dock and install a replacement gyroscope. It also will carry supplies for the station and return with accumulated junk. Three space walks also are planned, one of which will be used to test new techniques to repair damage to the shuttle's insulating tiles.
Discovery's seven-member crew flew in Saturday, a day early, to skirt the fringes of Hurricane Dennis and continue last-minute preparations for their flight.
Shuttle commander Eileen Collins said it was time for the spacecraft to launch again.
"It's very important for humans to get off the planet," said Collins, who is making her third flight.
She said the crew would carry with them a photograph of the Columbia crew and would pray for them each day. She hinted that there would be other memorials for the lost astronauts that Discovery's crew was keeping to themselves.
"We will always remember our friends," Collins said in the interview. "But it's time to move on."
Thousands of tourists and members of the media have arrived for the scheduled 12:51 p.m. PDT launch, packing hotel rooms as far away as Orlando, 45 miles off.
Business owners in nearby Titusville, who have long depended on the sprawling, 140,000-acre space center for their livelihoods, are delighted.
Kennedy officials said this launch would only be exceeded in terms of media attendance by a handful of launches, including the Apollo 11 mission and the shuttle flight of former senator and astronaut John Glenn.