A camera in Endeavour's payload bay shows the international space station. The Raffaello cargo module the main feature seen in this view. The Spacelab pallet is also visible on the end Canadarm2 near the shuttle's nose. Photo: Spaceflight Now/NASA TV

Revising an earlier decision to extend the shuttle Endeavour's flight by one day, NASA managers late today decided to extend the mission at least two days to give engineers more time to resolve ongoing computer problems hobbling the international outpost.

The plan, if agreed to by the Russians, would delay launch of a Soyuz spacecraft carrying millionaire space tourist Dennis Tito by at least one day and possibly longer.

"For folks who like to fly in space, I think I have what is good news for the Endeavour crew," astronaut Cady Coleman radioed from Houston shortly after 7 p.m. "We are going to stay docked another day, that would be two total, and plan on undocking on flight day 12 (Monday) and landing on flight day 14 (Wednesday).

"That gives us some time to get our arms around our computer situation and really get a good look at what's going on before we decide to do MPLM and SLP ops," she told station astronaut Susan Helms and shuttle flier Chris Hadfield.

Coleman was referring to delayed work to move a cargo module from the station to the shuttle's payload bay for return to Earth and additional work with the station's newly installed robot arm to hand a no-longer-needed cargo pallet to Endeavour's robot arm for reberthing in the ship's cargo bay.

"Our plan presently is if we can get comfortable tomorrow we would do MPLM (cargo module) ops and the soonest we would do SSRMS (station arm) ops with the SLP (Spacelab Pallet) would be the next day after that," Coleman said.

"Well, Chris is pretty happy," Helms replied. "And Alpha's pretty happy."

"Well I should actually couch that with words that we are pending Russian concurrence, they would have to move their Soyuz launch," Coleman said. "And so we're looking for that concurrence and folks are working real hard to make sure everything is coordinated. But right now that's our plan."

Tito and his two cosmonaut crewmates are scheduled for launch Saturday from the Baikonur Cosmodrome. It takes two days for a Soyuz to catch up with its target and docking was expected Monday morning.

But under the current plan, Endeavour will not leave the station until Monday, which would prevent the Soyuz from making an on-time launch. That's because the Russian spacecraft would have to pass with 20 feet or so of the shuttle's vertical tail fin during final approach and it is not known how that might affect the ship's rendezvous radar, radios or other systems.

The decision to extend Endeavour's mission was based on a desire to make absolutely sure the space station's computers can be restored to normal operation after a series of subtle glitches that crippled the outpost Tuesday evening.

Bill Gerstenmaier, deputy manager of the space station program at the Johnson Space Center in Houston, said the team has two goals: To restore computer redundancy before attempting to undock the Raffaello cargo module; and to gain additional run time on the computers to make sure the software will remain stable over the long haul.

To recap the basic problem: As of 7:45 p.m., just one of the Destiny lab module's three command-and-control computers was operational. In addition, two computers in the Unity module were off line because of a timing synchronization problem.

An artist's concept shows the historic "handshake" between the station and shuttle robotic arms as the Spacelab pallet is handed from Canadarm2 to Endeavour's crane. Photo: CSA

The two node computers, running an emergency program called Mighty Mouse, were responsible for getting C&C-2 back in operation in Destiny after all three of the station's command computers shut down in domino fashion Tuesday night and Wednesday. But C&C-2's input-output capability was deliberately inhibited while engineers studied the situation.

As a result, the computer's internal clock got out of synch with clocks in the Unity computers. When engineers attempted to reboot the Unity machines this afternoon, they immediately shut down, believing there was a problem.

Gerstenmaier said engineers have developed a plan to get the node computers and C&C-2 back in synch this evening. Assuming that work goes well, engineers will attempt to re-establish the station's S-band communications link in order to reprogram one of the two off-line command computers.

All of that will take nine or 10 hours, Gerstenmaier said, assuming all goes well.

The idea is to have two C&C computers on line and operational, along with both node computers, before allowing C&C-2 to drive the motorized bolts holding the Raffaello module in place.

If the computer failed midway through that process, the backup C&C machine could take over. And if that computer failed, the node machines could step in.

Once the cargo module is berthed, engineers will focus on gaining run time on the C&C computers to ensure they will continue working normally. The computer system is required to operate the station's new robot arm and if all goes well, the arm will be powered up Saturday to hand the cargo pallet back to Endeavour's robot arm.

"We've got a large group of folks ... all around the country that are working on these computer software issues," said flight director Wayne Hale. "It's a great challenge. We kind of wish we didn't have this kind of challenge but at the same time, the response has been great, everybody's been working very hard. We're going to resolve these little obstacles on the way to success and get the station all operational before we leave."

If all goes well, that is. And so far, that's turned out to be a big if.