A launch-pad camera captures a close-up view of the shuttle Challenger's liftoff on Jan. 28, 1986. From this camera position, a cloud of gray-brown smoke can be seen on the right side of the solid rocket booster, directly across from the letter "U" in "United States" on the orbiter. This was the first visible sign that a breach in the booster's joint may have occurred. Investigators determined that frigid overnight temperatures caused the booster joints' normally pliable rubber O-ring seals to become hard and non-flexible. The failure of the seals caused hot exhaust gases to blow through the joints, cutting into the external fuel tank.