an obscure shock-wave phenomenon called shock-shock interaction comes into play. When a reentering spacecraft breaks apart, hundreds of pieces—none with the carefully planned aerodynamics of the intact craft—are flying at hypersonic speeds, creating a chaotic web of shock waves. Clark likened them to the bow waves behind a water-skier’s boat. At the nodes of these shock waves—the places where they intersect—the forces add together with savage, otherworldly intensity. “It
