[Dan in Pasadena]

Tyson,
At one time, before the Shuttle was operational, there was a plan to make the entire crew compartment - somewhat like a giant capsule ala the Apollo and Gemini programs, able to be jettisoned away from the rest of the Orbiter in the event of a terminal emergency. In fact, this crew compartment IS a sealed unit that contains the breathable environment and it DID jettison away in the Challenger disaster...but not intentionally. It can be seen in the photos of the explosion right as it pulls apart...which is one of the reasons some or possibly all of the astronauts were alive all the way down.

This feature was done away with due to cost and other considerations. The Orbiter also had/has the capability of getting the astronauts out on an emergency basis while still on the launch pad via detonation cord in the crew compartment windows and what amounts to long wires that they shoot down off the gantry on...think of James Bonds sliding down a wire.

One of the secondary sources of explosion during the Challenger disaster were large hydrazine spherical tanks that are the fuel for smallish ignitors or "jets" that micro-fire as neened in orbit to manuever the Orbiter. The hemispheres of these tanks used to be made at Marquardt here in L.A... actually in Van Nuys. The detonation cord I mentioned above was made at a place that used to be called Explosive Technology in Fairfield, near Sacramento. I don't know how much this stuff has changed over the years, I've been out of the aeropsace business for 15 years but I used to be intimately involved. What I can say for sure is that the Shuttle program is old, old , OLD tech. It was originally designed in the early 70's. Too long ago for it to be still in use in my opinion.