NASA (search) plans to launch the first space shuttle flight in 21/2 years, even if it is plagued by the same fuel gauge problem that halted the previous countdown two weeks ago, officials said Sunday.

Discovery is set to lift off Tuesday at 10:39 a.m., the same time Columbia took off on its doomed mission in 2003.

Deputy shuttle program manager Wayne Hale (search) said the fuel gauge problem has been a vexing one — engineers still don't know exactly what caused it — and he's repeatedly asked himself, "Are we taking care enough to do it right?"

"Based on the last 10 days' worth of effort, the huge number of people and the tremendous number of hours that have been spent in testing and analysis, I think that we're coming to the right place," he said.

At an evening news conference, Hale and other NASA officials found themselves defending the decision to launch with a fuel gauge failure. They stressed that they will proceed with a liftoff only if the problem is well understood and involves the gauges in question — anything else will result in a postponement.

NASA's own launch rule — in place since the 1986 Challenger disaster (search) — requires that all four hydrogen fuel gauges in the external tank be working properly. Going with three out of four would result in a "deviation" of the rule, Hale told reporters.

"I am committed — and I think the whole team is committed — to doing this in a safe manner," Hale said. "I think we're all still struggling a little bit with the ghost of Columbia, and therefore we want to make sure we do it right."

NASA Administrator Michael Griffin said he supports the decision and even hopes the problem recurs to further pinpoint the source of the trouble. He acknowledged that the public might perceive that the space agency is rushing to launch, but insisted it was the right technical judgment.

"These are rather arcane matters, I would admit. They're rather difficult and sometimes they don't always present well," Griffin said. "But in the long run, I think if it's the right thing, we can explain it to you, and you want us doing what's right, not what necessarily is obvious or popular."

Workers last week repaired faulty electrical grounding inside Discovery in hopes that would solve the fuel gauge problem that thwarted the first launch attempt on July 13. One of the four gauges failed a routine test two hours before the scheduled liftoff. Technicians also swapped the wiring between the troublesome fuel sensor and another one to better understand the issue if it reappears Tuesday.

The same type of problem occurred back in April during a fueling test and was written off as an "unexplained anomaly."

The fuel gauges are needed to prevent the main engines from shutting down too soon or too late during liftoff, in the event of an extreme problem like a leaking tank. The first scenario could result in a risky, never-attempted emergency landing; the second could cause the engine turbines to rupture and, quite possibly, destroy the spacecraft.

Only two fuel gauges are needed to avoid such dangerous situations, but NASA normally requires all four to be working at liftoff for redundancy.

Hale conceded there is no way to know with 100 percent certainty that more fuel gauges will not conk out on the shuttle's climb to orbit, if NASA launches with only three functioning ones. But that would involve stacking up multiple failures, he noted, "and the odds become kind of in the acceptable risk category that we have to go fly with."

One person at Sunday's mission-management meeting, which was led by Hale, had concerns about the fuel gauge issue and expressed them in an anonymous suggestion box. Hale said the matter was addressed and, in the end, the group came to a consensus — "I would almost say unanimity" — that the game plan was good.

NASA has just one week to launch Discovery and its crew of seven to the international space station, before putting off the mission until September.

The space agency is insisting on good lighting in order to see any signs of the type of launch damage that crippled Columbia. The opportunity for good photography, both at Cape Canaveral and over the North Atlantic when the fuel tank separates nearly nine minutes after liftoff, diminishes in August and is unacceptable until Sept. 9.

Columbia and its seven astronauts were brought down by a broken section of fuel-tank foam insulation that struck just over a minute after liftoff and proved lethal during descent two weeks later, on Feb. 1, 2003.

Forecasters, meanwhile, put the odds of good launch weather Tuesday at 60 percent, with rain and clouds as the main concerns. What's more, the weather at the overseas emergency landing sites is not looking good at all.

Hale refused to put his own odds on the chance of a liftoff.

"My observation is that when the weather is good, you have vehicle problems. If the vehicle works, you have weather problems," he said, smiling. "Since we have some weather concerns, I'm confident the vehicle is going to be OK."