There were initially seven built: one structural test rig (never left the ground nd was destroyed), one flight test airframe (Enterprise) and then the five service orbiters. Challenger was destroyed, and a replacement spaceframe was ordered to replace it.

Who knows if there can be a replacement this time. There should be: if Bush has any sense of proportion, then maybe he should think about not rushing into a war which no-one supports and re-direct his attention to the space program to ensure the livelihoods of engineers all over the US. This would ensure our future, not a bloody oil war!!!