Still baffled by a fuel gauge failure, NASA (search) on Friday delayed the launch of its first space shuttle mission in 2 1/2 years 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.

Mission managers expected to meet later in the day to plot their next strategy and settle on a target launch date for Space Shuttle Discovery (search). The shuttle's seven astronauts, meanwhile, planned to return to Houston on Saturday and wait it out there.

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.

It was the latest setback in NASA's grueling and drawn-out effort to return to space and recover from the Columbia disaster (search) which killed all seven astronauts on Feb. 1, 2003. NASA has made a multitude of safety improvements to the aging shuttle to avoid future catastrophes — efforts that have repeatedly delayed the mission.

But it was an unrelated matter — a fuel gauge that read full instead of empty — that caused Wednesday's launch postponement.

NASA officials had held out hope, however slim, that they might be able to launch Discovery this weekend or early next week. But with engineers no closer to figuring out why the fuel sensor acted up, the space agency had no choice but to call for a lengthy standdown.

"They haven't found anything new," Buckingham said, "but they're still searching for answers."

The space agency is up against the clock. If extensive repairs are needed and the shuttle has to be moved off the launch pad and into the hangar, the flight could end up being bumped into September.

The timing of a launch is a complicated process, controlled partly by the location of the international space station, Discovery's destination. The shuttle must take off in daylight to ensure good camera views — a requirement for spotting any damage. That's one of the many changes called for by the Columbia accident investigators.

Twelve teams of engineers around the country pored through data Friday for clues as to why one of four hydrogen-fuel gauges in Discovery's external fuel tank malfunctioned during a routine pre-launch test Wednesday.

The 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 is to focus on testing new safety and repair methods and delivering supplies to the international space station.

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."

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. On Friday afternoon, technicians were just getting into Discovery to check the electronic box.

The fuel gauges are critical and even though only two are needed, all four must be working properly for a launch to proceed. Deputy shuttle program manager Wayne 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 replaced.

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, said Hale.

He said NASA wanted to avoid such a test now on the shuttle's new and stronger turbopumps.

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.

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.