I think that "environamentalism" and NASA efforts to "improve" the shuttle to meet these goals may have responsible for the loss of both Challenger and Columbia.I think that the following facts are correct, but I do not know that with absolute certainty, so I am running this by HZ.

In the case of Challenger, the asbestos based joint compound was replaced with a non-asbestos based compound, and then this replacement was not properly tested before flight. As is now known, the design of the O-rings was faulty in the first place, and it is likely that the asbestos based compound was the only thing that had not prevented earlier catastrophic failure.

In the case of Columbia, the freon based propellant for External Tank insulation was replaced. In this case, stnad alone system testing was probably impossible, but then the in flight failures of the new tank insulation system were not observed and reported up the safety chain. In addition, problems with the new tank insulation application were not reported either.

So fundqamentally, the question that I am looking for HZ feedback on is, were NASA's attempts to improve the shuttle to deal with "environmental" concerns mistakes, or simply mistakenly implemented? Is there a specific general failure mode, one common to both losses, that needs to be looked at? Does it have any application to efforts aimed at upgrading the shuttles' reaction control systems, or any other shuttle upgrades?