CAPE CANAVERAL, Fla. -- Revealing emails from some of NASA's top bosses express how dangerous the shuttle really is. Despite the concern, Tuesday afternoon, NASA said they'll continue to fly.

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The emails make it clear that the exact same problem that delayed the space shuttle launch last week could have posed a danger since the start of the shuttle program more than 25 years ago. The problems are with the fuel sensors at the very bottom of the shuttle's external tank.

Now, NASA will try to fix the problem on a very tight deadline. They announced the problem is so serious, they are going to run a fueling test next Tuesday on the launch pad, a complete about-face from proposals made last week to try and fly regardless of the fuel sensors.

After the space shuttle launch was scrubbed last Friday because of a faulty fuel sensor system in the shuttle's external fuel tank, some of NASA's top brass considered flying the shuttle regardless. But in an external email, head of NASA's Office of Safety and Assurance Bill McArthur wrote, "Right now I'm far from being comfortable with flying in our current condition."

In another email, Wayne Hale, the head of the shuttle program, also expressed extreme concern about the shuttle's safety, writing that they have spent three years trying to fix the problem to no avail: "Having completed everything that we can think of to do, we must come to the place where we have to consider what it means to fly with an unreliable system."

The sensors, which work like the low fuel light in your car, shut down the shuttle's main engines before they run out of liquid hydrogen, over heat and explode. Tuesday in a telephone news conference, Hale said his feelings have changed.

"Our thinking has evolved from Friday, early Friday, when I wrote that little note and I think there is quite a lot that we can do yet to troubleshoot and perhaps make this system work," Hale said.

Hale acknowledged in his email that the problem may have made shuttle flights riskier than previously thought, writing, "It is likely that this system has been unreliable all along. It seems to me likely that we have been flying the entire history of the program with a false sense of security."

So how important are the sensors? There have been cases in the past where they've studied the shuttle's performance and they came close to needing those sensors to shut down the engines before there was a disaster.

Atlantis is still scheduled to launch on January 2.