[pdonis]

> If those were unmanned test flights pushing the vehicle limits

As far as the launch to orbit, which was the flight phase when Challenger was lost, every Shuttle flight pushed the vehicle to its limits. That was unavoidable. There was no way to do a launch that was any more stressful than the actual launches were.

[zardo]

You can push the environmental conditions of the launch e.g. winds and temperatures.

[pdonis]

See my response to Mauling Monkey upthread on why the cold temperature of the Challenger launch actually wasn't the major issue it was made out to be.

Note also my comments there about other SRB designs that were known well before the Shuttle and the range of temperatures they could launch in. Those designs were used on many unmanned flights for years before the Shuttle was even designed. So in this respect, the unmanned test work had already been done. The Shuttle designers just refused to take advantage of all that knowledge for braindead political reasons.