…m insulation (SOFI) fell from one of the ramps that attached the shuttle to its external fuel tank. As the crew rose at 28,968 kilometres per hour the piece of foam collided with one of the tiles on the outer edge of the shuttle’s left wing.
A quick technical correction here. ~28,968 kph (~18,000 mph) is roughly the orbital velocity of the Space Shuttle. Columbia was traveling at 2,523 kph (2,300 ft/s) at the time the foam from the external tank impacted the leading edge of the Shuttle’s wing.
NASA notes that “The visual evidence shows that the debris impacted the wing approximately 0.161 seconds after separating from the ET. In that time, the debris slowed down from 2300 fps to about 1500 fps, so it hit the orbiter with a relative velocity of about 800 fps. In essence, the debris slowed down and the Orbiter did not, so that the Orbiter ran into the debris.”