Space Shuttle Solid Rocket Booster - Challenger Disaster

Challenger Disaster

The Challenger accident originated with a design flaw and system failure of one of its SRBs. The cause of the accident was found by the Rogers Commission to be a faulty design of the SRB joints compounded by unusually cold weather the morning of the flight. The commission found that the large rubber "O-rings" in SRB joints were not effective at cold temperatures like those of the January 1986 morning of the accident (36 °F (2 °C)). A cold weather-compromised joint in the right SRB failed at launch and eventually allowed hot gases from within that rocket booster to sear a hole into the adjacent main external fuel tank and also weaken the lower strut holding the SRB to the external tank. The leak in the SRB joint caused a catastrophic failure of the lower strut and partial detachment of the SRB, causing a collision between the SRB and external tank. With a disintegrating external tank and severely off-axis thrust from the right SRB, traveling at a speed of Mach 1.92 at 46,000 feet, the Space Shuttle stack disintegrated and was enveloped in an "explosive burn" (i.e., rapid deflagration) of the liquid propellants from the external tank. The Orbiter broke into several large pieces as a result of "severe" aerodynamic forces.

During the subsequent downtime, detailed structural analyses were performed on critical structural elements of the SRB. Analyses were primarily focused in areas where anomalies had been noted during postflight inspection of recovered hardware.

One of the areas was the attachment ring where the SRBs are connected to the external tank. Areas of distress were noted in some of the fasteners where the ring attaches to the SRB motor case. This situation was attributed to the high loads encountered during water impact. To correct the situation and ensure higher strength margins during ascent, the attach ring was redesigned to encircle the motor case completely (360 degrees). Previously, the attachment ring formed a 'C' shape and encircled the motor case just 270 degrees.

Additionally, special structural tests were performed on the aft skirt. During this test program, an anomaly occurred in a critical weld between the hold-down post and skin of the skirt. A redesign was implemented to add reinforcement brackets and fittings in the aft ring of the skirt.

These two modifications added approximately 450 lb (200 kg) to the weight of each SRB. The result is called a "Redesigned Solid Rocket Motor" (RSRM).