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30 years later: Remembering the Challenger's crew and NASA's darkest hour

On Jan. 28, 1986, one of the worst tragedies in NASA's history occurred when the space shuttle Challenger broke apart over Atlantic waters 73 seconds into its ascent, resulting in the deaths of all seven crew members onboard.

"We mourn seven heroes: Michael Smith, Dick Scobee, Judith Resnik, Ronald McNair, Ellison Onizuka, Gregory Jarvis, and Christa McAuliffe. We mourn their loss as a nation together," President Ronald Reagan said in a speech delivered the night following the disaster.

"The crew of the space shuttle Challenger honored us by the manner in which they lived their lives. We will never forget them, nor the last time we saw them, this morning, as they prepared for their journey and waved goodbye and 'slipped the surly bonds of Earth' to 'touch the face of God,'" he said in his closing comments.

The catastrophic failure of Challenger's tenth mission, STS-51L, was a direct result of a faulty joint between the two lower segments of the right Solid Rocket Booster, or SRB, according to the Rogers Commission Report.

As the shuttle ascended in the atmosphere, it encountered high-altitude wind shear conditions that lasted for about 30 seconds of the flight.

"The specific failure was the destruction of the seals that are intended to prevent hot gases from leaking through the joint during the propellant burn of the rocket motor," the report states.

Once the seal failed, hot gas began to leak, ultimately leading to the structural failure of the external tank. As a result, the orbiter began to disintegrate off the coastline of Cape Canaveral.

Environmental factors likely contributed to the malfunction of rubber O-Rings, which were designed to keep the joint in the booster sealed, according to the commission investigation.

Record low temperatures across the region had dipped into the low 20s F the night before, and were hovering near freezing in the area on the morning of Challenger's ill-fated launch.

Ice had even accumulated on the launch pad the night before, and needed to be checked and removed by crews prior to liftoff.

While the O-rings used return to their uncompressed shape in higher temperatures, the temperatures on the morning of launch likely prevented the O-rings in the right SRB from following the opening of the gap between the joint at the time of ignition.

"Sealing without any gas blow-by did not occur consistently until the temperature was raised to 55 degrees Fahrenheit," according to the commission report on O-ring performance. "O-ring hardness is also a function of temperature and may have been another factor in joint performance."

The air temperature at liftoff, 11:38 a.m. EST, was 36 F, which was 15 degrees below temperatures of any previous launch. The investigation also revealed that the low temperatures had two effects that could have potentially affected the seal performance, which include O-ring resiliency degradation, and the potential for ice in the joints.

The temperature at the coldest point on the joint of the right SRB was estimated to between 23 to 33 F at the time of ignition, while the temperature on the opposite side facing the sun was estimated to be at around 50 F.

"Just after liftoff at .678 seconds into the flight, photographic data shows a strong puff of gray smoke was spurting from the vicinity of the aft field joint on the right solid rocket booster," NASA reports in STS-51L mission profile. "This area of the solid booster faces the external tank. The vaporized material streaming from the joint indicated there was not a complete sealing action within the joint."

Analysis of the photographs also indicates the O-rings were destroyed shortly after ignition.

"The black color and dense composition of the smoke puffs suggest that the grease, joint insulation and rubber O-rings in the joint seal were being burned and eroded by the hot propellant gases," NASA reports.

However, while temperature might have been a contributing factor in the failure of the O-rings, engineers had seen partial failures of the O-rings prior to the Challenger launch on other missions with warmer weather. Unfortunately, even though a written recommendation advising against a shuttle launch at temperatures below 53 F was given due to fears of O-ring and joint failure, those in charge of Challenger mission were not aware of the potential problem.

"If the decision-makers had known all of the facts, it is highly unlikely that they would have decided to launch 51-L," according to the report.

The heartbreaking Challenger disaster not only changed the way NASA operated, it also impacted the lives of millions around the nation, and is remembered as one of the American space program's darkest days.

"The future is not free: the story of all human progress is one of a struggle against all odds. We learned again that this America, which Abraham Lincoln called the last, best hope of man on Earth, was built on heroism and noble sacrifice. It was built by men and women like our seven star voyagers, who answered a call beyond duty, who gave more than was expected or required and who gave it little thought of worldly reward," President Ronald Reagan said on Jan. 31, 1986.