LOOK CLOSELY at the photo:

This rare close-up view of the liftoff of the Shuttle Challenger on mission STS-51L. From this camera position, a cloud of grey-brown smoke can be seen on the right side of the Solid Rocket Booster (SRB) on a line directly across from the letter "U" in United States.  This was the first visible sign that an SRB joint breach may have occured.  On January 28, 1986 frigid overnight temperatures caused normally pliable rubber O-ring seals and putty that are designed to seal and establish joint integrity between the Solid Rocket Booster (SRB) joint segments, to become hard and non-flexible. At the instant of SRB ignition, tremendous stresses and pressures occur within the SRB casing and especially at the joint attachmentment points.  The failure of the O-rings and putty to "seat" properly at motor ignition caused hot exhaust gases to blow by the seals and putty. During Challenger's ascent, this hot gas "blow by" ultimately cut a swath completely through the steel booster casing; and like a welder's torch, began cutting into the External Tank (ET).  A chain reaction of events occurring in milliseconds culminated in a massive explosion.  The orbiter Challenger was instantly ejected by the blast and went askew into the supersonic air flow.  Though it was concluded that the G-forces experienced during orbiter ejection and break-up were survivable, impact with the ocean surface was not. Tragically, all seven crew members perished.