The Challenger shuttle disaster that killed 7 crew members was 40 years ago. What happened and how they're being remembered.

Forty years ago, the U.S. space shuttle Challenger set out on a mission to not just launch satellites but to carry the first teacher into space and to inspire the promise of spaceflight into classrooms. The seven crew members reflected a broad spectrum of American society, including two women, the first Asian American astronaut and the second Black astronaut.

One of the women was set to be the first teacher in space and was planning to conduct experiments and teach lessons from the Challenger space trip. The main goal of mission STS-51-L was to launch a second Tracking and Data Relay Satellite. It also carried the Spartan Halley satellite that was supposed to be released by the shuttle, observe Halley’s Comet during its closest approach to the sun and then be picked back up by the Challenger two days later.

But shortly after launch on a cold and clear Florida morning, Challenger exploded, killing all seven crew members. It became one of the most devastating moments in U.S. history.

What happened?

On Jan. 28, 1986, Challenger lifted off from Cape Canaveral, Fla. It had been delayed until 11:38 a.m. ET due to thick ice on the launch pad after central Florida experienced a severe cold wave the night before.

A catastrophic failure occurred 73 seconds after liftoff as the shuttle emerged from “Max-Q,” the period of highest mechanical stress in the lower atmosphere. The vehicle broke apart in flight and exploded into a fireball. All seven aboard the shuttle were killed, and searches revealed no sign of the crew.

Crew consisted of 7, including a high school teacher

Commander Francis R. “Dick” Scobee

Pilot Michael J. Smith

Mission Specialist Ellison S. Onizuka

Mission Specialist Judith A. Resnik

Mission Specialist Ronald E. McNair

Payload Specialist Gregory B. Jarvis

Payload Specialist Christa McAuliffe, a high school teacher from New Hampshire

McAuliffe was chosen from thousands of applicants to represent educators in space as part of NASA’s Teacher in Space Project. This captured the public’s attention and made the launch particularly high profile. Hundreds of people watched the launch in person, while schoolchildren across the country watched it live in classrooms from NASA live feeds or through cable news network CNN, which was new at the time, according to History.com. Americans who weren’t able to watch it live during the traditional workday saw it through taped replays.

What happened in the aftermath?

A special presidential commission investigated the cause of the Challenger disaster, resulting in the Rogers Commission Report, which was released to President Ronald Reagan on June 9, 1986. The investigation found that the explosion was caused by the failure of an O-ring seal on one of the solid rocket boosters. The cold weather on launch day rendered the rubber seals faulty, allowing hot gases to escape and igniting the main liquid-fuel tank.

The report also found communication breakdowns were partly to blame. A number of engineers testified that they had expressed concern about the reliability of the seals and warned that cold conditions for the Jan. 28, 1986, launch could cause failure.

The investigation faulted NASA overall, while contractor Morton Thiokol, which manufactured the booster motors and assembled them at the Kennedy Space Center, was also implicated.

NASA shuttle flights were suspended for nearly three years before resuming, while solid rocket boosters were redesigned and new safety protocols and organizational changes were implemented to better communicate and execute engineering concerns.

40 years later, the astronauts' families still mourn

Every year, near the end of January, NASA observes an annual Day of Remembrance to honor the crews of Apollo 1 and space shuttles Challenger and Columbia. NASA Administrator Jared Isaacman said in a news release, “We remember them not to retreat from risk, but to respect it — to learn, to improve, and continue onward. Their sacrifice and the strength of their families will forever inspire us as we continue to reach for the stars and pursue the secrets of the universe.”

As part of NASA’s Day of Remembrance, mourners of the crew members killed in the Challenger accident gathered at the Kennedy Space Center for a memorial ceremony last week to honor them.

Alison Smith Balch, the daughter of pilot Michael Smith, tearfully said that her life changed forever on that fateful cold January day, the Associated Press reported. “In that sense,” she said, “we are all part of this story.”

“Every day I miss Mike," his widow, Jane Smith-Holcott, told mourners. “Every day's the same.”

A fellow contender for the Teacher in Space Project attended the memorial, remembering fellow teacher McAuliffe. “We were so close together,” said Bob Veilleux, who is a retired astronomy high school teacher from McAuliffe’s home state of New Hampshire.