With one last fiery blast from its massive main engines and one last, iconic, 180-degree roll after liftoff, the space shuttle Atlantis and its four-member crew roared into orbit Friday to begin the final voyage of the 39-year shuttle program.

The primary goal of the 12-day mission is to make a final delivery run to the International Space Station, leaving it as stocked as possible. Although the Europeans, Japan, and Russia will continue to deliver supplies in the shuttle's absence, none of their vehicles have the cargo capacity a shuttle could deliver.

The mission also provides insurance against any delays that might occur as commercial companies take cargo-delivery, and eventually the crew-delivery, batons from NASA.

With an eye toward the future, the shuttle also is carrying experimental gear to demonstrate an ability to robotically refuel satellites not originally designed for in-orbit top-offs. Such a capability would extend the life of expensive communications satellites, which would drop down to the station's altitude from higher orbits. But it also figures in plans for human space exploration, which often envision an in-space fueling or refueling capability.

Despite concerns about the weather – including a direct hit on the pad by lightning on Thursday – and a last-seconds halt to the countdown because of a false reading from a key piece of hardware on the launch pad, the launch was essentially picture-perfect.

To Kennedy Space Center Director Robert Cabana, the launch preparations, as well as the launch itself, were testament to the professionalism of a launch team working in the face of enormous personal uncertainty as the center's duties shift and the workforce shrinks dramatically.

"Change is hard," he says. "We're going to have more folks walking out the door here in the next few weeks."

Still, "they've performed their jobs absolutely flawlessly right up to the end. That says a lot for them."

The sense of finality was evident from the launch director's last comments to the shuttle crew in the waning minutes of the countdown to the slow, reluctant departure of the launch team from the control room after Atlantis cleared the pad.

"It did take awhile to leave the control room," said Michael Leinbach, the mission's launch director. "It seemed like we didn't want to leave; it was like the end of a party, and you just don't want to go. You just want to hang around just a little bit longer and relish our friends and what we've accomplished" in the 30 years the shuttles have been operating.

Despite criticism in Washington and among several spaceflight veterans that a post-shuttle NASA has little or no sense of its next steps, officials maintain that they are taking concrete steps toward preparing to explore a new set of destinations.

The Orion capsule, one of the centerpieces of an exploration architecture established under President George W. Bush, remains on the books to sit atop a new "heavy lift" rocket the agency is designing to reach beyond low-Earth orbit, the International Space Station's domain.

In a statement following the launch, President Obama noted that while the shuttle program is ending, "I have tasked the men and women of NASA with an ambitious new mission: to break new boundaries in space exploration, ultimately sending Americans to Mars. I know they are up to the challenge – and I plan to be around to see it."

Yet in a period when the nation's fiscal woes top the political agenda, meeting that challenge may be difficult.

One signal came Wednesday with the release of a draft budget appropriations bill for fiscal 2012 from the GOP-led House appropriations subcommittee, which has jurisdiction over NASA.

The committee is proposing to spend slightly more than $1 billion for the Orion program, and nearly $2 billion for the new heavy-lift rocket NASA is working on. That is more than the administration sought in its fiscal 2012 proposal. But the levels represent cuts from the sum recommended in an authorization bill Congress passed last October.

If enacted, the cuts could stretch out the program, raising its overall costs and delaying the day Mr. Obama plans to be around to see.

In addition, the draft budget holds no money for two programs NASA has implemented for nurturing the private launch efforts on which the agency has pinned its space-station cargo- and crew-resupply hopes. This means that NASA will have to shuffle money around internally, as it did this fiscal year, to keep those programs going.

Much can happen between a draft appropriations measure from one subcommittee of one branch of Congress, and a final, reconciled appropriation bill a president signs, cautions William Gerstenmaier, NASA's associate administrator for space operations.

Still, he says, "We understand the tough environment and we'll work with that ... and be prepared to execute what we get when we finally get an answer from Congress."