One suspected reason for the change in damage, according to reports by Katnik and outside organizations that helped Kennedy Space Center study the issue, is NASA changed the way it "foamed" the external tank sometime shortly before that mission in an effort to be more environmentally friendly by reducing the use of ozone-depleting materials. "Freon was used in the production of the previous foam," he reported. "This method was eliminated in favor of foam that did not require freon for its production. MSFC is investigating the consideration that some characteristics of the new foam may not be known for the...