All future space shuttle flights have been grounded by NASA because of foam that flew off Discovery's fuel tank while lifting off. This is precisely what caused the Columbia catastrophe:

"Call it luck or whatever, it didn't harm the orbiter," Parsons said. If the foam had broken away earlier in flight when the atmosphere is thicker, increasing the acceleration and likelihood of impact it could have caused catastrophic damage to Discovery.

"We think that would have been really bad, so it's not acceptable," said Parsons' deputy, Wayne Hale. He said every indication so far is that Discovery is safe for its return home.

Yeah, it would have been bad.

I haven't been comfortable with this mission since I learned that NASA was prepared to bend its own rules, and launch Discovery even if the fuel gauge problem that delayed the mission a week ago recurred. NASA argued that it would be justified in doing so if it determined that there was nothing fundamentally wrong with the shuttle. But it didn't foresee this, did it? What else has NASA not foreseen?

A full scale investigation must be launched to determine precisely why this problem - basically identical to that which happened to Columbia - has again occurred. The investigation should not be conducted by NASA, but by a panel appointed from the outside. It must be completely independant of NASA.

Hopefully, the rest of the mission will go perfectly, any possible damage has not been grave, and the Discovery will return safely to earth. Prayers are in order for the crew of the Discovery.

One would hope that NASA has begun to think about a completely new design, from the ground up, for the type of spacecraft which will carry humans into space from this point on.

It's time to retire the space shuttle. It has seen its day, and completed its honorable service, but that service should now be at an end. An entirely new blueprint for a space vehicle is in order. Discovery is the last space shuttle that should ever be launched.

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Related:

Discovery Is Off
NASA Determined To Launch Even If Problem Recurs
NASA May Launch Discovery Despite Fuel Gauge Failure

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Update: NASA was warned at the end of June of the debris shedding problem:

A task force established by NASA to monitor the agency's safety improvements after the 2003 disaster concluded on June 28 that the agency "did not meet" the requirement of a team of accident investigators that the agency "eliminate all . . . debris shedding." It noted pointedly that the external fuel tank, attached by metal struts to the shuttle during its violent launch, "still sheds debris that could potentially cripple an orbiter."

And yet they still they launched Discovery, fully prepared to bend their own rules, and launch even if the fuel gauge failed again.

Is this unbelievable or what?