NASA said Friday it would not try to launch the space shuttle Discovery until late next week — at the earliest.

The space agency is backing out of the countdown and has given up trying to make a launch attempt anytime soon, said spokesman Bruce Buckingham.

As mission managers expected to meet later in the day to plot their next strategy and settle on a target launch date, hundreds of NASA (search) engineers scrambled to figure out why a fuel gauge on space shuttle Discovery (search) failed just before its scheduled liftoff.

Most likely, NASA's first mission since the 2003 Columbia disaster will require more complicated repairs and be delayed into next week or even September, depending on the extent of work needed.

"Everybody is tremendously disappointed," said Michael Wetmore, director of space shuttle processing. "But everybody was also here 2 ½ years ago and saw that we failed in our mission to protect the crew. So there's no one who wants to go forward with a potential risk to the crew that hasn't been appropriately analyzed and addressed."

NASA remains stumped as to why one of four hydrogen-fuel gauges in Discovery's external fuel tank malfunctioned during a routine pre-launch test Wednesday.

Watch "Discovery: Return to Space," a one-hour special on the FOX News Channel, on Saturday at 9 p.m. and 12 a.m. EDT.

The seven astronauts were already on board, liftoff was little more than two hours away and the astronauts' families, members of Congress and space buffs around the world were eagerly waiting. The 12-day mission was loaded with interesting challenges that called for testing new safety and repair methods and delivering supplies to the international space station (search).

But everything came to a halt when launch controllers sent information mimicking an empty fuel tank. One of the fuel gauges remained stuck on "full."

Hours later, long after the tank was emptied, the troublesome gauge finally started working. That makes it an intermittent problem, deputy shuttle program manager Wayne Hale said, "which is the worst kind of thing to troubleshoot."

The problem could be in the gauge at the bottom of the tank — an electronic box aboard the shuttle that serves as a data-relay hub — or in the cables and wires in between.

The fuel gauges are critical and even though only two are needed, all four must be working properly for a launch to proceed. Hale said these low-level fuel gauges never failed until April, when two malfunctioned during a fueling test of Discovery's original tank. That tank was later replaced for other safety reasons.

If the fuel tank was empty but the sensors indicated full, the engine turbines would spin too fast and likely rupture — possibly damaging the tail of the spacecraft and dooming the crew. A ground test that accidentally caused that to happen back in the early 1980s resulted in severe "uncontained" damage, Hale said.

NASA is loath to repeat such a test on the shuttle's new and stronger turbopumps, Hale said.

On the other end of the scale, if the sensors were to trigger a premature shutdown of the main engines on the way to orbit, the shuttle would be forced to attempt a dangerous emergency landing in Europe or elsewhere.

"None of those options are really what you'd like to have happen to you," Hale said.

Workers will need to enter Discovery's engine compartment to get to the electronic box that is associated with the fuel gauges. The box contains transistors that may not have been assembled correctly.

NASA has a spare box ready to put in, but the device is exhibiting a signal interference problem and may not be reliable. If engineers have to put together a box from scratch, the work could take anywhere from 10 days to three weeks, Hale said.

It will be considerably more complicated if workers have to reach the fuel gauges themselves inside the tank.

NASA is up against the clock. If Discovery isn't flying by the end of July, the shuttle must remain grounded until September to ensure a daylight liftoff for good camera views — a requirement for spotting any damage during launch. That's one of the many changes called for by the Columbia accident investigators.

When Columbia blasted off on its doomed mission, NASA had no clear pictures of the foam insulation hitting the left wing and knocking a hole in it. The gash caused the spacecraft to break apart during re-entry on Feb. 1, 2003, killing all seven astronauts.

Watch "Discovery: Return to Space," a one-hour special on the FOX News Channel, on Saturday at 9 p.m. and 12 a.m. EDT.