Wheels Stop

The Astrovan, carrying the STS-135 crew, passes the launch control center and press site en route to the pad.

So far, everything is going well for today’s launch. Tanking was completed at 5 am without incident, and no technical problems have been reported. The forecast still has only a 30% chance of acceptable weather, but the weather so far is cooperating, with some breaks in the clouds and even a little bit of sun this morning. There’s a subtly growing sense of optimism that the weather just might hold this morning, although liftoff is not for more than three hours. The crew left crew quarters at a little after 7:30 am and boarded the Astrovan to go to the pad. Right now they are in the process of boarding the shuttle, as things by all appearances are going as planned.

NASA officials brief the media about the status of the STS-135 countdown on Wednesday morning. (NASA/KSC)

At the L-2 (i.e., two days before launch) briefing Wednesday morning, NASA officials made it clear that, for now, only one thing was standing between them and a launch Friday morning of Atlantis: the weather. The briefing took place after a short Mission Management Team meeting that ended with unanimous consent to continue the countdown. “The vehicle is in fantastic shape,” Mike Moses, chair of the MMT, said at the briefing. Mike Leinbach, the shuttle launch director, said they discussed only minor technical issues at the meeting, none of which would be a constraint to launch.

Weather, though, is another story. “It is not looking favorable right now for launch,” Kathy Winters, shuttle weather officer, said at the briefing. The concern is with a tropical wave moving to the north, bringing with it clouds, rain, and some thunderstorms, although nothing severe. As of the briefing there is only a 30% chance of acceptable weather at launch time Friday; in addition, there’s the possibility of thunderstorms on Thursday afternoon that could delay the retraction of the rotating service structure (RSS) that envelops the orbiter while on the pad. The forecast does improve for Saturday (40% of acceptable weather) and again Sunday (60%).

Despite the dismal forecast, shuttle officials retained some optimism about launching on Friday. “I know of only one way to make it a 100% no-go forecast, and that is not to put propellant into the tank,” Moses said. In the past, he said, there have been times when they have fueled the shuttle with only a 10% chance of acceptable weather, and still were able to launch. “A forecast is a forecast, and even 12 hours out its still a forecast,” he said.

Currently, NASA has only until Sunday to launch Atlantis, after which time it must stand down for a Delta 4 launch from nearby Cape Canaveral, scheduled for Thursday. There has been speculation that NASA might negotiate with the Air Force to delay the Delta launch to give NASA an extra day or two, but Moses said there’s been no discussion yet about that. “Nothing happens until we can’t go on,” he said. Later, he suggested that, if grounded by weather or other issues, NASA would be willing to wait until after the Delta launch to try again. “At the end of the day, ultimately, there is no harm in not launching in front of this Delta. If we have to go to the other side of it, we’ll go to the other side of it.”

One reporter asked if a series of weather or other scrubs might be welcomed by the shuttle workforce, as it keeps the program alive–and for many of them, keeps their jobs–for a little while longer. Moses disagreed. “There’s no feeling that a scrub is a good thing,” he said.

“Right now I feel pretty good about trying on Friday,” Moses said, despite the forecast. “But we’re not at Friday yet, so I’m not going to commit to anything until we get to Friday.”

The Mission Management Team gave their unanimous approval this morning to proceed with the launch of Atlantis on Friday morning. However, the weather forecast is getting a little worse: forecasts now are calling for only a 30 percent chance of acceptable weather at launch time, down from 40 percent yesterday. (On the bright side, that means that there’s nearly 1 chance in 3 the weather will be okay. Optimism!) Clouds and the potential for showers and even thunderstorms remain the key weather issues. We should get more details later this morning at the L-2 countdown briefing, starting at 11:30 am EDT and airing on NASA TV.