A hole may need to open in the clouds at just the right time for Atlantis to fly on the final Shuttle mission tomorrow morning.
At Wednesday’s pre-launch briefing to the media NASA managers said the weather forecast had worsened overnight to a 70 percent chance of stormy conditions that would postpone the planned 11:26 am (16:26 BST) launch.
But in the past Space Shuttles have blasted off from Kennedy Space Center with much worse odds. "It could be pouring rain everywhere in the county, and if we get that hole in the right spot at the right time, we can go," said Mike Moses, NASA’s launch integration manager.
He described Atlantis as being in "fantastic shape" for launch as the so far trouble-free countdown continued with teams loading chemical reactants into Atlantis’ power-producing fuel cell system.
Three orbiter fuel cells will generate electricity for Atlantis and its four person crew during the 12 day mission to stock the International Space Station with food and spare parts.
At 2 pm today, crews plan to swing open the rotating gantry at launch pad 39A to reveal Atlantis, poised for the Shuttle programme’s 135th launch in 30 years.
Fuelling of the craft’s 15-story external tank should then begin about 12 hours later — assuming managers give the go-ahead after a weather briefing at 1:30 am Friday morning.
"I only know of one way to make it a 100 percent no-go forecast, and that’s to not put propellant in the tank," said Moses.
If the weather doesn’t cooperate Friday, the outlook improves slightly Saturday and Sunday.
After that, NASA plans to pause until at least July 16 to let the Air Force launch a satellite from Cape Canaveral — but if it comes to the crunch the two parties might negotiate freeing up most of next week for Atlantis.
But launch director Mike Leinbach said his teams weren’t hoping for delays. "Friday is game day for us, so we don’t want to wait until Saturday," he said. "We want to play the game Friday."
Also playing on managers' minds are the huge crowds expected on Florida’s Space Coast to view the final ascent — and the impact that mass of people could have on launch operations.
Local police expect half-to-three-quarters of a million people travelling to the area and, because of the heavy traffic that would be generated, Leinbach is reserving the option to skip a Saturday launch try out of concern the launch team could not get home and make it back to the spaceport in time for a 24 hour turnaround.
Weather officer Kathy Winters said she expected conditions to improve over the weekend, with a 40 percent chance of good weather on Saturday and a 60 percent chance Sunday.