CAPE CANAVERAL, Fla. – The launch of the space shuttle Discovery was pushed back into late next week after NASA managers decided Friday they could no longer hold engineers and launch workers in a continual countdown status.

“We are on a day-by-day basis,” said N. Wayne Hale Jr., deputy shuttle program manager.

He insisted, however, that “we are not in any sense of the word becoming pessimistic about meeting the July (launch) window,” which ends July 31.

“We have the entire resources of the agency behind us,” he added.

National Aeronautics and Space Administration managers said they have more than 100 items on the so-called “fault tree” left to look at to determine what caused the failure of a fuel sensor just two hours before Discovery’s scheduled launch Wednesday.

A dozen engineering teams are working on the problem, which first arose during a test in April, when two sensors failed. The sensors are designed to shut off the liquid hydrogen fuel before the engines run dry.

After that failure, NASA managers swapped out a new external fuel tank and thought they had solved the problem. Instead, another sensor, one of four monitoring hydrogen fuel levels, failed during countdown.