Re: Using Alcohol fuel instead of hydrogen
If the external tank stored kerosene instead of hydrogen it would be 1/4th the volume, and wouldn't need any insulation.
If the external tank stored isopropyl alcohol instead of hydrogen it would be 3/8th the size, and also wouldn't need any insulation, and the main engines would have indefinite stop & re-start capability for the duration of the mission.
And if the shuttle had an escape capsule comprising the entire forward cabin of the shuttle, then the crew would have a secondary re-entry vehicle. See my graphic representation entitled "Shuttle2" in my webfolder.