The shuttle could not pass the tests that SpaceX will demonstrate. Post-Challenger, it was substantially improved, but still had survivability gaps and questions whether the some of the abort modes were truly survivable (especially under the more severe conditions). http://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Post-...
While the SRBs were burning, the shuttle could not abort at all. This is the ascent period when the Challenger was lost.
After the SRBs detached, there were several options to abort, all of them assuming the shuttle was mostly functional. For the first four shuttle launches, the shuttle had ejection seats so the astronauts (two, anyway :-O) could escape a crippled shuttle. http://en.wikipedia.org/wiki/Space_Shuttle_abort_modes
It looks like the Apollo system had good abort coverage. http://en.wikipedia.org/wiki/Apollo_abort_modes
The shuttle could not pass the tests that SpaceX will demonstrate. Post-Challenger, it was substantially improved, but still had survivability gaps and questions whether the some of the abort modes were truly survivable (especially under the more severe conditions). http://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Post-...
The best the astronauts could do on the launch pad was a "zip line" escape http://americandigest.org/mt-archives/american_studies/how_t... (with scary pictures: http://www.collectspace.com/ubb/Forum30/HTML/001111.html).
While the SRBs were burning, the shuttle could not abort at all. This is the ascent period when the Challenger was lost.
After the SRBs detached, there were several options to abort, all of them assuming the shuttle was mostly functional. For the first four shuttle launches, the shuttle had ejection seats so the astronauts (two, anyway :-O) could escape a crippled shuttle. http://en.wikipedia.org/wiki/Space_Shuttle_abort_modes