But uneasy memories were stirring of briefings, years ago, about top-down failure cascades. The classic example being the Twin Towers, which had collapsed in toto despite the fact that all the initial damage had been confined to their upper floors. Debris from a high-level event could damage structural elements far below, with incalculable results. The thin, almost nonexistent atmosphere up here would allow debris to fall at supersonic velocity. Energy, and damage, would increase as the velocity squared…
