In the very nick of time, engineers recovered use of a critical hard drive aboard the international space station late Saturday and then restored a third command-and-control computer to operation, clearing the way for shuttle Endeavour to finally undock from the outpost at 1:34 p.m.

Command-and-control computer No. 2's hard drive was recovered late last night as an 11 p.m. deadline approached to inform Russian flight controllers orchestrating the approach of a Soyuz spacecraft carrying tourist Dennis Tito whether Endeavour would be undocking today or Monday.

NASA managers said Saturday they needed at least two operational C&C computers and at least one working hard drive, or mass storage device - MSD - before Endeavour would be cleared for undocking. Otherwise, the shuttle would remain attached for one more day and the Russians would have to modify the Soyuz rendezvous timeline to set up a Tuesday docking.

As it turned out, it was a moot point. Two of the station's three main computers already were working and engineers at the Johnson Space Center in Houston coaxed a hard drive in one of the machines - C&C-2 - back into operation as last night's deadline approached.

Early this morning, they reloaded C&C-1 with control software and while its hard drive is not yet operational, the station has three functional C&C computers and one hard drive, clearing the way for Endeavour to depart.

"For both crews, here's the C&C status," astronaut Lisa Nowak radioed the astronauts shortly after wakeup today. "It's good news. C&C-2 is fully functional, including MSD. It's in primary right now. The caution and warning configuration is fully restored with all the proper messages inhibited and suppressed.

"C&C-3 has no changes, it's in backup but still with no MSD. C&C-1 is in standby. It's loaded, but we had a little trouble formatting the disk. We got a disk format error on the MSD. We think it's OK, but we're going to dump it to analyze. Once we verify that that MSD is OK, we're going to swap the status of C&C-1 and 3. C&C-1 will go to backup and C&C-3 will go to standby."

"OK, that's pretty clear," replied station astronaut James Voss.

"And the bottom line to that is we are go for undocking today," Nowak said.

"Well, that's good but it's also bad," Voss mused. "We're going to really be sad to see these guys go, we've enjoyed having them with us up here on Alpha. One quick one, have we gotten to the bottom-line (computer) problem yet, have we figured that out?"

"Not yet, Jim, and we're going to have some procedures coming on board to create a couple of backup (C&Cs) just in case there are more problems."

"OK. Do they think it's hardware related or software?"

"It's initially looking like a hardware problem because we're having problems with the MSDs on C&C-1 and 3, the hard drives are not spinning up," Nowak said.

NASA flight controllers have said throughout the station's computer ordeal that a software problem of some sort was believed to be the culprit. It's not yet clear whether Nowak was referring to the overall problem or the trouble getting two of the hard drives operational.

In any case, the astronauts on both crews were allowed to sleep late today, waking up at 5:11 a.m. to begin a final few hours of joint activity.

After one more meal together, hatches between the two spacecraft will be closed at 11:11 a.m. and Endeavour will undock at 1:34 p.m. After a loop around the outpost to photograph the complex with a large-format IMAX camera, Endeavour will depart for good at 2:34 p.m.

Pilot Jeffrey Ashby will be at the controls.

"This is one of the more interesting tasks that I have to do," he ssaid in a NASA interview. "I will be manually flying the undock, separation and the maneuver around the international space station.

"As the shuttle separates, I will manually fly directly out from the docking port to a distance of about 400 feet. And then I will fly an arc around the space station to a point where we are looking directly down upon the top of the space station at a distance of about 400 feet.

"At that point we intend to execute a maneuver which places the nose of the shuttle to the Earth. And, as we drift around behind the space station, we are hoping to catch a moment where we can take a short IMAX scene of the space station as it passes through the horizon of the Earth. It's a spectacular view."

The Soyuz TM-32 spacecraft, meanwhile, is continuing its two-day rendezvous with the station. If all goes well, Tito and his two crewmates - Talgat Musabayev and Yury Baturin - will dock with the space station a few minutes before 4 a.m. Monday.