Safely??

The Challenger disaster could perfectly well have been avoided if they had been willing to look. There was a clear indication of substantial deviation from design and the joint could have been engineered to stay in compression during the twang.

But Columbia was fundamental. There was an awful lot of insulation aerodynamically before the heat shield. Once again, multiple warnings, but keeping the insulation from being torn off while keeping the weight down was problematic. Columbia was the beginning of the end as they realized they couldn't sweep it under the rug anymore and they couldn't truly fix it.

Challenger could also have been avoided simply by not launching in conditions that were known to be out of spec.

> The Challenger disaster could perfectly well have been avoided if they had been willing to look.

The tragedy of Challenger is that Morton Thiokol engineers did look enough to know that the O-ring design was likely to fail under cold weather conditions. This was already a known issue and the engineers specifically recommended that Challenger postpone launch because of the temperature at the pad the night before the launch.

They got overruled... almost certainly for what amounts to political reasons as the big bosses didn't want to throw off the timing of the media-hyped "first class being taught in space".