Which is why I mentioned the VentureStar
It wouldn't be possible to get another shuttle airborne in such a short period of time. As for Kim's thoughts on the OSP, I was under the notion that it took a fairly long time to put an expendable launch vehicle together. He knows far more about it than I, and I could be wrong.
A SSTO vehicle based on X-33 technology could be wheeled out, raised vertically, fueled, then launched, all within a short period of time. Such a short reaction time would prove essential in a space rescue.