Atlantis on STS-27 holds the distinction of being the most heavily damaged spacecraft to return safely from orbit. The cork tip of the right-hand SRB fell off during ascent and gouged the side of the orbiter. More than seven hundred tiles were damaged, and one was knocked off completely. During reentry, plasma completely melted through a steel antenna cover under the missing tile and had started melting the skin of the orbiter, but Atlantis passed through the period of peak heating before its airframe was breached.
