I think the whole grounding is a kneejerk reaction to please the media and congress rather than having any real safety reasons.
It's almost certain that shuttles have always been hit by flying debris to some extent, and the damage was extremely minor (shuttles have made it back safely with large sections of their heatshield missing in the past, the little dents and scratches seen now are nothing in comparison).
That's not to say a replacement is way overdue of course. The initial plans when designing the shuttle system was for it to be replaced by the late 1980s.
Its intended replacement was almost ready to fly (awaiting the delivery of a final component and final assembly) when it was cancelled (X-33/VentureStar).
In fact, NASA and the US government under Clinton (mainly) seems to have done what it can to make sure the US human space program is killed off completely (note that the decision to kill VentureStar came just before Clinton left office, a final stab in the back of the pro-space people in the Republican party).
For a design that's almost 30 years old, the shuttle is performing remarkably well.
About the only thing where the shuttle didn't deliver as planned/hoped for was launch cost. This is still several orders of magnitude higher than it should be for a commercially viable system, far more than expected. In large part this is caused by the extremely long maintenance cycles needed between flights, making rapid turnaround (and thus high vehicle utilisation) impossible (the original estimates had called for a few weeks at most, the turnaround time is now nearly half a year).
The accident rate (2 accidents in over 100 launches) is low for space launchers (it's still too high of course, but it's better than the existing alternatives).
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duckman
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