Complex sentence: Although O'Connor said there were still unresolved concerns that foam insulation could break off of the external fuel tank and damage the orbiter, Griffin characterized the risk as acceptable, arguing that it would be better to test one change at a time.
Split into simpler sentences: Although O'Connor said there were still unresolved concerns that foam insulation could break off of the external fuel tank and damage the orbiter, Griffin characterized the risk as acceptable. Griffin argued that it would be better to test one change at a time.