Challenger lifted off at 11:38 EST exactly. In the first four seconds of flight, grey smoke was seen on the launch pad cameras coming out of the aft (bottom) field joint in the right booster. This was the O-rings being partially destroyed - they had been frozen solid and could not seal, so the blow-by of hot gases burned them away completely before the "extrusion" could happen. However, aluminium oxide, formed by the burning rocket fuel, plugged the gap and formed a weak seal. "Challenger" was safe for now, and quickly cleared the launch tower.