This is a photo of the top of the aft sgement of the right hand solid rocket booster, (SRB), fown on the disastrous STS-51-L mission. It shows the seal which is thought to have leaked, causing the destruction of the Challenger Shuttle and the death of its entire crew. A ring of yellow putty can be seen at the top of the segment. Below this and separated by a layer of grease are the two O-rings which are thought to have failed due to the extremely low temperatures experienced by the right booster before launch.