The Italian-made Raffaello cargo module could be returned to Endeavour's payload bay later today. Photo: Spaceflight Now/NASA TV

The international space station's one working command-and-control computer turned over control of the station's orientation to the shuttle Endeavour's computers early today as part of an ongoing procedure to revive Alpha's still-crippled computer system.

While Endeavour works to boost the station's altitude by about two miles, the Destiny module's lone operational C&C computer - C&C-2 - will re resynched with its guidance and navigation system machines and engineers will press ahead with work to re-initialize one of the lab's other two C&C computers.

The third C&C computer - C&C-1 - is believed to have a failed hard drive. It will be replaced with an identical computer that normally would be used to control scientific equipment in the Destiny lab module.

Once all of that is done, the space station will have a fully operational computer system for the first time since Tuesday night when C&C-1 suddenly dropped off line, triggering a domino-like cascade of failures that crippled the complex.

Because engineers do not yet know exactly what caused the initial failure, computers controlling laboratory experiments and the station's new Canadian robot arm will not be allowed to talk to the C&C machines until engineers verify their software is bug free.

In Russia, meanwhile, ground crews are readying a Soyuz spacecraft for launch to the space station carrying two cosmonauts and millionaire space tourist Dennis Tito. Liftoff is scheduled for Saturday with a docking on Monday.

NASA mission managers asked their Russian counterparts Thursday to delay the flight by one day, allowing the Endeavour astronauts to spend an extra two days docked to the station while ground engineers complete thorough tests of the station's computer system.

As of 6 a.m. today, however, the Russians had not yet agreed to delay Tito's flight.

NASA insiders say if the Russians fail to honor the request - which the U.S. agency considers essential to ensuring the long-term health of the outpost - already strained relations between the station partners will erode even more.

In the meantime, Endeavour will remain docked to the station at least through Sunday morning, one day longer than originally planned. If the Russians agree to delay the Soyuz flight by one day, Endeavour will not undock until Monday.

The three-seat Soyuz serves as the station crew's lifeboat. The Russian spacecraft are only certified for 180 days in orbit and the lifeboat currently attached, which was launched on Oct. 31, is at the end of its orbital lifetime.

Tito and his two crewmates are known as a taxi flight crew. They will deliver a fresh Soyuz to the station, spend about a week on board the outpost and then return to Earth in the current return vehicle. At issue is whether the Russians will agree to put one more day of orbital life on the current Soyuz.

But for Endeavour to remain docked for an additional two days, the Soyuz flight must slip. The Soyuz cannot dock to the station while the shuttle is attached because it would have to pass close to Endeavour's vertical tail fin on final approach and it's not known how that proximity might affect the Russian craft's radar and other systems.

In the meantime, assuming the overall computer reconfiguration work goes well today, the Endeavour astronauts will demate the Raffaello cargo module around 2:41 p.m., using the shuttle's robot arm to place it back in Endeavour's cargo bay for return to Earth.

At least two C&C computers must be operational before Raffaello can be undocked from the Unity module's downward-facing port. While a single computer can operate the motor-driven bolts holding the cargo module to the station, flight controllers want at least one operational backup in place in case additional problems crop up.

Additional tests of the new Canadarm 2 space crane will be deferred until Saturday when station arm operator Susan Helms will hand a 3,000-pound cargo pallet back to the shuttle's robot arm for reberthing in Endeavour's payload bay.

Helms then plans to put the arm through a dry run of procedures that will be needed in June to install the station's main airlock. The arm work also requires at least two operational C&C computers.

The computer problems began Tuesday night when C&C-1 suddenly had problems accessing its internal hard drive and then crashed. C&C-2 took over but it, too, had hard drive problems and began acting erratically. Flight controllers then switched to C&C-3, which soon experienced similar problems and dropped off line, taking the station's main communications system down with it.

The C&C computers provide critical telemetry to the ground and carry out the commands needed to reconfigure various space station systems. Working in the blind using backup communications paths, flight controllers finally managed to bring C&C-2 back on line late Wednesday. Forty minutes later, however, it shut down again.

At that point, unknown to ground engineers, a program running in two computers inside the Unity node detected that all three C&C machines were down and automatically began cycling power on and off in a bid to force one of the computers to reboot.

The so-called Mighty Mouse program worked, and C&C-2 rebooted from scratch using pristine software. Engineers spent the rest of the day Wednesday restoring communications, studying telemetry and developing a plan to revive the other computers.

Overnight, engineers resynchronized the two node computers with C&C-2 and re-established the station's S-band communications system before handing attitude control over to the shuttle this morning.