Mission specialist Rick Mastracchio inside the Spacehab module located in Atlantis' payload bay. Photo: NASA

The Atlantis astronauts were awakened at 7:46 p.m. EDT to begin their final day of work outfitting and assembling the international space station. The crew will begin shutting internal hatches and turning out the lights shortly after midnight, starting with a Progress supply ship docked to the far end of the lab complex.

Working their way back toward the shuttle some 13-stories "below," a 12th and final hatch will be closed around 8:30 a.m. EDT Sunday, setting the stage for undocking around 11:44 p.m. EDT that evening.

"They're going to button up the station, they're going to back out and make sure they have the right pressures across all the hatches and shut everything down gracefully," said lead station flight director Mark Ferring. "That's going to take the lion's share of the day.

Here's how astronaut Daniel Burbank summed up the final day of work in a pre-flight NASA interview:

"When we do the egress activities themselves, we're going to be leaving the space station in a very specific, pre-planned configuration, with certain hatches closed, with valves in a certain configuration that would be necessary so that the ground, if there were a problem, could command those remotely," he said.

"And we're going to basically be sweeping our way through the space station, kind of an all-hands evolution, tidying everything up and making sure all the cargo that we've got there is secured and ready to go and ready to receive the next mission."

But first, Burbank and his crewmates plan to move a few final items into the station, including special desserts for the station's first full-time crew. Commander Terrence Wilcutt and pilot Scott Altman also will fire Atlantis's steering jets late this evening to boost the station's altitude - currently 228.9 by 236.9 miles - by about 3.5 miles.

Their crewmates, meanwhile, plan to test a high-tech vibrationless exercise treadmill called TVIS that was installed early Saturday and do a bit of housekeeping before leaving.

"They will complete a final TVIS (treadmill) checkout, they will be changing out some filters in the dust collector system in the Zarya (module), they'll also be changing out the harmful contaminant filter in the Zarya," Ferring said.

In the reverse sequence from a week ago, commander Terry Wilcutt will close each station module hatch while egressing from the outpost. Photo: NASA

The final hatch between Atlantis and the space station should be closed by 8:30 a.m. Sunday.

Before leaving, however, the astronauts plan to bump up the station's air pressure to 14.9 psi, "getting the station holding as much gas as possible," said shuttle flight director Phil Engelauf.

"In addition to that repressurization, as we do the backout we'll be setting up the tools on the shuttle flight deck in anticipation of undocking," he said.

If all goes well, Atlantis will undock from the orbital complex at 11:44 p.m. Sunday, six days after the crew first entered the lab last Monday. Altman plans to guide Atlantis through two loops around the station for a detailed photo survey before departing for good around 1:30 a.m. Monday.

Weather permitting, Atlantis is scheduled to land back at the Kennedy Space Center around 3:50 a.m. Wednesday.

Just two weeks later, on Oct. 5, the shuttle Discovery is scheduled to blast off on the 100th shuttle mission, a complex four-spacewalk flight to equip the space station with a set of stabilizing gyroscopes.

"It doesn't seem like it's been a hundred flights," mused Bill Gerstenmaier, manager of shuttle program integration. "But it has, and we've learned a tremendous amount during all those years. I think it's kind of fitting that the 100th flight comes during the build up of the space station.

"The space station is also kind of a new era here for manned space flight for us and it's neat to see that bridge from the shuttle," he said. "We've done tremendous things with the shuttle, it's been an unbelievably versatile vehicle. Then to see it carry on and start building space station, which is really a huge endeavor for us, is really a neat thing to see."

Meanwhile, NASA officials Saturday were keeping a close eye on Hurricane Gordon churning in the Gulf of Mexico. Workers at the Kennedy Space Center were making preparations to roll space shuttle Discovery off its launch pad and back to the safe confines of Vehicle Assembly Building on Sunday if Gordon threatens to bring high winds to the Cape.