Ultrasound inspections of the shuttle Endeavour's robot arm show small areas of delamination where an access platform hit the crane earlier this week during insertion into the ship's cargo bay to fix a leaking oxygen line. Shuttle program manager Ronald Dittemore said tonight Endeavour's launch was delayed to no earlier than next Friday to give engineers more time to assess the severity of the arm problem and to confirm the fatigue-related crack in an oxygen line flex hose is not any sort of generic, fleet-wide problem.

"We did decide to move the launch date to no earlier than the 22nd of November," he told reporters during an evening teleconference. "We continue to have two open issues and we're in different stages of converging to a solution on both issues."

But Dittemore said he expects results by Monday and at that point, he should be better able to assess the odds of actually launching Endeavour next Friday.

"The folks are going to work the weekend, both on the RMS (robot arm) and on the O2 system leak recovery," he said. "Monday is going to be a big day for us."

NASA had hoped to launch Endeavour on a space station assembly and crew rotation flight last Monday morning. But late Sunday, as the crew was strapping in for launch, engineers decided a leak in one of two lines that feed oxygen to the ship's crew cabin was unacceptable for flight and the countdown was called off.

Analysis indicated the leak was most likely in a section of tubing just below the floor of the forward end of the payload bay. A cargo access platform was inserted into the bay to give engineers a place to work. But as the platform was being maneuvered into position, one of the workers serving as a "spotter" to help guide the platform into place apparently got distracted while repositioning himself, allowing the platform to hit Endeavour's fragile 50-foot-long robot arm.

"It was human error," Dittemore said. "We had spotters in place and those spotters are required to call a time out, or a halt, if we get too close to structure. This particular person got distracted at the time that it was getting close to the structure and it was a mistake."

A section of protective insulation was torn and while the oxygen line repair work continued, a second troubleshooting effort was initiated to assess the damage to the robot arm. Overnight Thursday and into today, engineers gained access and cut away a 4-inch by 5-inch section of the honeycomb outer layer to permit ultrasound examinations of the arm's carbon-composite structure.

"The honeycomb bumper damage is of no concern," Dittemore said tonight. "That layer is just what it means, it's a bumper layer, it provides no structural support. So cutting it out just allows us access to the inner surface.

"We have completed preliminary ultrasonic testing of the area of concern and we have seen some small areas of delamination. That delamination does not mean it is unacceptable. It just means at this point we need to go in there for some further testing to see to the degree that the delamination implies some concern to us whether the structural integrity of the boom has been compromised. At this point, we do not know that. ... We do not have data that says the arm has been impacted to the point that we cannot use it or cannot fly it.

Additional ultrasonic tests are planned over the weekend. At the same time, another group of engineers is looking at possible backup plans in case the arm ultimately is deemed unflyable.

The worst-case scenario would require hauling Endeavour back to its hangar so another arm could be installed in place of the one currently on board. A rollback, Dittemore said, would delay launch five to six weeks and, in all likelihood, force NASA to delay launch until early January.

That's because the shuttle cannot be launched to the space station between Dec. 11 and Dec. 25 due to what is known as a "beta angle cutout." The beta angle is the angle between the plane of the station's orbit and the sun and it determines the amount of electricity the lab's arrays can generate. During cutout periods, the station cannot generate enough power for joint operations with the shuttle. A six-week delay to haul Endeavour to its hangar, swap out robot arms and return the ship to the pad would put launch well into the December beta angle cutout, forcing a delay to early January.

Another option, however, would be to simply remove the arm at the launch pad and fly the mission without it, using the station's Canadarm2 space crane to pull Endeavour's payload - a 45-foot-long, 14.5-ton solar array truss segment - from the orbiter's cargo bay for attachment to the station. This option, assuming it is even possible, would delay launch two to three weeks, Dittemore said.

The STS-113 flight plan currently calls for the shuttle's arm to pull the P1 truss from the payload bay because one of its support struts physically blocks the station arm from directly grappling the beam. If the shuttle arm and its central support strut were simply removed, Dittemore said the station arm could pull P1 from its perch in the cargo bay. Such a decision would require additional training for Kenneth Bowersox, commander of the next full-time station crew and the prime operator of Canadarm2 during P1's installation.

But Kennedy Space Center sources say it would be extremely difficult, if not impossible, to safely remove the robot arm at the launch pad. If that assessment is correct, NASA must either clear the arm for launch next week "as is" or stand down for the year. But the analysis continues and it's too early to say how this might play out.

As for the oxygen line investigation, Dittemore said preliminary analysis shows NASA probably is not facing a fleet-wide problem that could trigger a lengthy delay. He said the line in question includes three sections: A stainless steel central tube and metal-sheathed flex hoses at each end. The leak occurred in the flex hose connecting the line to a fitting in the crew cabin's aft bulkhead.

The oxygen line, and a nitrogen line that is structurally connected to it, are free to move, Dittemore said, because they are not anchored down as one might expect. As a result, the lines have experienced the vibrations of launch 18 times. The oxygen line apparently cracked due to vibration-related fatigue. Engineers do not believe any other flex hoses in the shuttle are subjected to similar launch loads.

Workers already have replaced the leaking oxygen hose. Just to be on the safe side, Dittemore said, they will replace the associated nitrogen line over the weekend. They also have removed a similar hose from the shuttle Discovery and plan to remove a corresponding section from Atlantis to find out if any similar problems are present.

As of this writing, no other flex hose problems have been found.

"We use the flex hoses in a lot of different applications in different systems throughout the ship," Dittemore said. "However, what's different about this particular failure is as we have come to look at the configuration, it's apparent to us we have a weak configuration that actually ties two flex hoses together and doesn't mount it to hard structure. Typically, if you have a flex hose you would hard mount it to structure so it doesn't vibrate and induce motion that would result in fatigue."

The lines in question aboard Endeavour are connected at both ends by flex hoses "so they are free to move in the middle between two flexible hoses holding them to structure. We tied those two lines together (when Endeavour was built), the O2 and the N2, but we never made the connection of the mounting to a hard point. If we'd mounted it to a hard point, we would have contained the motion. ... So we believe this particular configuration is probably the culprit. It does not indict all flex hoses throughout the vehicle and we have no data in our database that shows we're having problems with flex hoses in other parts of the vehicle. So we think it's configuration dependent."

Engineers are working through the weekend to make absolutely sure no similar configurations are present in other parts of the shuttle.