Editor's Note: This story was updated at 4:50 p.m. ET to reflect additional statements from NASA. Contrary to the previous report, NASA denies it is undertaking any effort to look specifically for sabotage.

NASA does not suspect sabotage was behind the glitch that twice delayed the launch of the space shuttle Endeavour recently.

The agency is investigating all possible explanations for the problem, but has no specific processes to search for intentional tampering, officials said.

"NASA is not concerned about sabotage at all," NASA spokesman Kyle Herring said. "They develop a detailed fault tree to try to come to a conclusion as to what the problem is. The program leaves no stone unturned in an investigative effort. There is never a fault tree that has a block in it that's labeled sabotage."

Endeavour's STS-127 mission was supposed to lift off June 13, but a leak of hydrogen gas from a pipe attached to the shuttle's fuel tank kept the vehicle grounded. NASA tried to launch Endeavour a second time on Wednesday, but again the leak appeared, even after workers replaced the leaky seal between the pipe and the shuttle.

The shuttle will now stand down until at least July 11 while investigators probe the cause of the failure, which also delayed the shuttle Discovery's STS-119 mission in March. That flight managed to blast off four days later than planned, after the seal swap-out apparently stopped the leak.

So far, the root cause of the issue is mysterious.

"We've got to step back and try to understand this problem," space shuttle deputy program manager LeRoy Cain said in a briefing after the second Endeavour delay. "I'm confident we will do that. We will be relentless in terms of trying to understand what's going on with this system."

While NASA fully expects to find a technical glitch at fault, its investigative processes will be able to detect any human-introduced error as well, if it occurred, Cain said.

NASA plans to retire its three aging space shuttles in 2010, though its next-generation spaceship, called Orion, will not be ready by then.

The agency began cutting shuttle-related jobs last month and expects to have to lay off a significant number of workers after the last shuttle flies. Because each shuttle launch delay has ripple effects on future scheduled flights, the stall with Endeavour has the potential to extend the shuttle fleet's end date. NASA is mindful that some workers may be under stress due to the situation.

"We have talked a great deal about those kinds of potential issues," Cain said. "And I think we're taking measures that are commensurate with the circumstances that we have here as we go forward this summer and for the rest of the shuttle program for sure."

He said he doubted anyone on staff would try to sabotage the program.

"I think that we've got a highly professional work force here, and to a person, at least when I talked to them, they're in this business because they love the work that they do and they love to support the human spaceflight endeavor."

A case of sabotage has occurred before, with a subcontractor working on the 2007 flight of Endeavour. NASA discovered a space station computer box that was intentionally damaged, with cut wires. They were able to repair the damage with no ill effects to the flight.

In this situation, though, NASA has stressed that there is no reason to suspect intentional tampering, and they are not taking any particular steps to investigate this possibility.

"We trust the people who work on this program and we'll do anything we can to help them understand and correct a problem," Herring said. "We know it's a dedicated work force. Any problems of any kind we would uncover through our normal checks and balances."

In response to any suggestion of sabotage, United Space Alliance, a major NASA contractor on the shuttle, released a statement.

"Any suggestion that our workforce would do anything to intentionally hinder a safe and successful launch is grossly irresponsible and completely off-base. The entire shuttle team worked extremely hard making the necessary repairs and preparing Endeavour for the July 17th launch attempt. It is a testament to their dedication, commitment and skill that the vehicle was in a position to go for the second attempt. Neither USA nor our NASA customer has any reason to suspect any wrongdoing of any kind, and there is no investigation being undertaken."

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