Well, it's not just a crack in the insulation of the shuttle Discovery. There are two cracks in the aluminum underneath. NASA hasn't put out a decision as of this moment, but they have never fixed damage of this type on the pad, so we're all going home for a while. The cracks are in the intertank section of the aerodynamic outer skin, where they can't damage the tanks, but this is going to slip the launch way past the latest hoped-for date of early December.
COMMENT: The Shuttle system, remarkably for a new space system, did not greatly overrun its R&D budget when it was under development. The problem is that our space leaders back in the 70s traded off R&D costs for operational costs and reliability by not developing the planned fully reusable two-stage system. Despite the great things achieved by the Shuttle, its astronauts, and its support crew, there is still a melancholy knowledge that the craft could have, and should have, been safer and cheaper to operate.