The most banal of problems led to an explosion that killed seven astronauts 73 seconds after takeoff on January 28, 1986.

The massive rubber rings were intended to contain the hot gases caused by burning rocket fuel.

The NASA space shuttle Challenger exploded 73 seconds after lift-off. (AAP)

But the stark temperature changes from a profoundly cold morning to the white-hot heat of take-off caused the O-rings to fail.

Before that day’s launch, the coldest takeoff had taken place on a 12-degree day. When the Challenger launched, it was -3 degrees.

Engineers were concerned about the effect of the cold weather on the rubber rings, but NASA pushed to launch the space shuttle anyway.

Part of the pressure to launch on that day was a scheduled broadcast of the takeoff being shown in schools across America.

The crew included teacher Christa McAuliffe.The crew included teacher Christa McAuliffe. (NASA)

For the first time a teacher was being sent to space.

Christa McAuliffe was selected out of 11,000 applicants as part of the Teacher in Space program.

McAuliffe was chosen so she could communicate with students in space.

But the program was not the original plan.

As a way to educate and engage with young children, NASA considered launching the Sesame Street character Big Bird into space.

Caroll Spinney, who played Big Bird and Oscar the Grouch, has retired from his role on Sesame Street.Caroll Spinney, who played Big Bird and Oscar the Grouch, was offered a trip on the Challenger. (Sesame Workshop/Robert Fuhring)”I once got a letter from NASA, asking if I would be willing to join a mission to orbit the Earth as Big Bird,” puppeteer Carol Spinney said.

“There wasn’t enough room for the puppet in the end, and I was replaced by a teacher.”

An estimated 2.5 million school children watched the Challenger blow up.

Though it was not apparent at the time, a study found at least some of the astronauts survived the initial explosion.

The Challenger disaster was a severe blow to the American space program. (AP)

“The crew of the space shuttle Challenger honoured 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.”

There were no further manned flights until September 1988.

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