Wondrium Looks at Engineering Failure behind Challenger Disaster

engineering failure, decision-making failure to blame for fatal launch

By Jonny Lupsha, Wondrium Staff Writer

In 1986, the space shuttle Challenger exploded 73 seconds after launch. All seven crew members aboard the space shuttle were killed. What caused the Challenger disaster and what did we learn from it?

Cold temperatures affecting the O-Rings in the solid rocket booster segment joints and poor decision-making led to the Challenger disaster. Photo by Kennedy Space Center / Wikimedia Commons / Public Domain

On January 28, 1986, the space shuttle Challenger launched from Cape Canaveral, Florida. Just 59 seconds after liftoff, a plume of flame emerged from the shuttle’s solid rocket booster. After another 14 seconds, the Challenger exploded, killing everyone on board. Following the disaster, it took two months to recover all seven astronauts’ remains and NASA delayed its missions for more than two years as it investigated and redesigned various shuttle features to prevent another tragedy.

What made the Challenger explode in the first place? Was it preventable? In his video series Epic Engineering Failures and the Lessons They Teach, Dr. Stephen Ressler, Professor Emeritus from the United States Military Academy at West Point, analyzes the Challenger disaster and those responsible.

What Caused Challenger to Explode?

The Challenger disaster had two critical errors that sealed its fate: an engineering failure and an organizational decision-making failure. The engineering failure centered on one of the solid rocket boosters (SRBs), which gave Challenger much of its extra thrust to take off.

SRBs are constructed from segments rather than built whole, and the point where any two segments meet is called a field joint. The small gap between the segments is sealed shut by a pair of “O-rings” made of heat-resistant synthetic rubber.

“The purpose of these O-rings was to prevent hot, high-pressure propellant gas from leaking out of the motor,” Dr. Ressler said. “The most ingenious aspect of this technology is that the O-ring, which was designed to contain the high pressure generated within the SRB, was also sealed by this same internal pressure.”

In testing, engineers saw that internal pressure led to a slight ballooning of the SRB segment’s steel casing, causing a gap to open between segments by just a few hundredths of an inch. This opening, called joint rotation, was just large enough to prevent the O-rings from sealing. NASA determined that using larger O-rings would solve the problem.

Throughout the early 1980s, several more problems emerged. In 1981, recovered O-rings showed signs of erosion. In 1984, recovered SRB materials showed proof that the first O-ring in one pair of O-rings had failed to seal. The secondary O-ring sealed successfully, but the implications were impossible to ignore.

The faulty O-rings were one of two major problems that led to the Challenger disaster.

Who Was Responsible for the Challenger Explosion?

The aerospace company responsible for the O-rings was called Thiokol. In response to continued and increasing problems with their O-rings, they formed an emergency task force to research the faulty part and develop a new kind of modified field-joint design.

“Although this new design had great promise, it was disapproved by NASA in September 1985 because of its cost, and even if it had been approved, it couldn’t possibly have been implemented prior to the STS-51L Challenger mission,” Dr. Ressler said. “And that brings us back to January 27, 1986—the eve of the ill-fated launch.”

Thiokol saw a consistent pattern in O-ring failure: low temperatures. When they heard that the Kennedy Space Center would fall to 18 degrees Fahrenheit that night and only get up to 28 degrees before the launch, they set up a conference call with NASA program managers from the Marshall Space Flight Center in order to recommend a postponement of the launch.

“Although this recommendation was entirely reasonable, it provoked an unexpectedly harsh reaction from NASA,” Dr. Ressler said. “Larry Mulloy angrily announced that he couldn’t accept Thiokol’s rationale, then added, ‘My God, Thiokol, when do you want me to launch—next April?’ George Hardy said he was ‘appalled’ by the recommendation.”

Thiokol eventually reversed its decision, saying that its research had been inconclusive. It’s believed that Thiokol did so as a business decision. Whatever the cause, Thiokol got on the same page as NASA and the launch proceeded to its fatal conclusion.

Epic Engineering Failures and the Lessons They Teach is now available to stream on Wondrium.