NASA launch managers this morning cleared space shuttle Endeavour to lift off before dawn Sunday from Kennedy Space Center in Florida, one of the five remaining flights before the shuttle program concludes this year or early next. The planned launch comes less than a week after the future of human spaceflight in the U.S. was shaken by President Obama, whose budget request for fiscal year 2011, released Monday, would cancel Constellation, the planned successor to the shuttle.

In its 13-day STS-130 mission Endeavour is set to deliver to the International Space Station (ISS) a module that will house many of the station's life-support systems as well as a panoramic observatory, or cupola, from which the station's robotic arm can be controlled. The module, formally designated Node 3, and the cupola together weigh some 13.5 metric tons. When the orbiter detaches from the station to head home, the ISS will be roughly 90 percent complete; the four shuttle missions following STS-130 will each bring the station one step closer to its finished state.

The cylindrical Node 3, also known as Tranquility, will also house exercise devices aimed at reducing the deleterious effects of weightlessness on bones and muscles. One of those devices is the COLBERT treadmill, delivered to the station in 2009 and named for comedian Stephen Colbert. At Colbert's encouragement, fans of the cable television host flooded an online NASA poll to help name the station's new node with write-in votes for "Colbert". NASA opted for the name Tranquility instead but appeased Colbert and his fans by naming the treadmill in his honor.

At a Friday morning news conference telecast from Kennedy Space Center, shuttle weather officer Kathy Winters said the forecast looked good for Endeavour's 4:39 A.M. launch. Winters said there was only a 20 percent chance that weather, in the form of high winds, would postpone launch. Shuttle launch integration manager Mike Moses said that earlier Friday morning the launch team had unanimously cleared the orbiter to blast off.

The six-member crew of Endeavour comprises commander George Zamka, pilot Terry Virts, and mission specialists Kathryn Hire, Stephen Robinson, Nicholas Patrick and Robert Behnken.

The final space shuttle mission is scheduled for September 16, but the probability of weather or technical delays in the intervening months make that launch likely to slip into 2011. Once the shuttle is retired, NASA will rely on the services of foreign partners, namely Russia, for manned missions in the near future. (Even if Constellation were saved from the budget ax, it would not be ready for manned launches before 2015 under the most optimistic scenarios.) With Obama's plan, commercial firms would instead step in once they demonstrate the ability to safely and cost-effectively deliver astronauts to orbit.

Obama's budget request would scrap Constellation but spare another massive project: the ISS. After more than a decade of construction and tens of billions of dollars, the ISS would have been dumped into the ocean in 2016 under existing plans and budgets, just years after completion; the president wants to fly the station through at least 2020. Bernardo Patti, ISS program manager for the European Space Agency, said he was very pleased about the station's potential life extension. The extra time, Patti said, is "going to give us a great opportunity to use to the full extent the ISS," which only last year was built out to its full capacity for six crew members.

During the Friday briefing, Moses and his colleagues fielded several questions from reporters on the shuttle program's end and what Obama's plan will mean for human spaceflight. "Every launch is a little bittersweet because we're one closer to the end," Moses said. He added that Constellation's proposed cancellation came as a surprise to many. "People are still a little bit shocked, still trying to digest that information and internalize it," Moses added.

Mike Leinbach, the shuttle launch director, said that worries about the future would not distract launch personnel from the task at hand. "We're going to play every down until the final whistle blows," Leinbach said, trotting out a football metaphor as he spoke about a launch scheduled for Super Bowl Sunday. "The team is ready to go. We will not be distracted on the consoles; we will not be distracted on the orbiter."