Criticism of The Space Shuttle Program - Accidents

Accidents

While the technical details of the Challenger and Columbia accidents are different, the organizational problems show similarities. In both cases events happened that were not planned for nor anticipated. Flight engineers' concerns about possible problems were not properly communicated to or understood by senior NASA managers. The vehicle gave ample warning beforehand of abnormal problems. A heavily layered, procedure-oriented bureaucratic structure inhibited necessary communication and action.

With Challenger, an O-ring that should not have eroded at all did erode on earlier shuttle launches. Yet managers felt that because it had not previously eroded by more than 30%, this was not a hazard as there was "a factor of three safety margin". Morton-Thiokol designed and manufactured the SRBs, and during a pre-launch conference call with NASA, Roger Boisjoly, the Thiokol engineer most experienced with the O-rings, pleaded with management repeatedly to cancel or reschedule the launch. He raised concerns that the unusually low temperatures would stiffen the O-rings, preventing a complete seal, which was exactly what happened on the fatal flight. However, Thiokol's senior managers overruled him, dismissing his safety concerns, and allowed the launch to proceed. Challenger's O-rings eroded completely through as predicted, resulting in the complete destruction of the spacecraft and the loss of all seven astronauts on board.

Columbia was destroyed because of damaged thermal protection from foam debris that broke off from the external tank during ascent. The foam had not been designed or expected to break off, but had been observed in the past to do so without incident. The original shuttle operational specification said the orbiter thermal protection tiles were designed to withstand virtually no debris hits at all. Over time NASA managers gradually accepted more tile damage, similar to how O-ring damage was accepted. The Columbia Accident Investigation Board called this tendency the "normalization of deviance" — a gradual acceptance of events outside the design tolerances of the craft simply because they had not been catastrophic to date.

The subject of missing or damaged thermal tiles on the Shuttle fleet only became an issue following the loss of Columbia in 2003, as it broke up on re-entry. In fact, Shuttles had previously come back missing as many as 20 tiles without any problem. STS-1 and STS-41 had all flown with missing thermal tiles from the orbital maneuvering system pods (visible to the crew). This image from the NASA archives shows many missing tiles on the STS-1 OMS pods. The problem on Columbia was that the damage was sustained from a foam strike to the reinforced carbon-carbon leading edge panel of the wing, not the heat tiles. The first Shuttle mission, STS-1, had a protruding gap filler that diverted hot gas into the right wheel well on re-entry, resulting in a buckling of the right main landing gear door.