The space shuttle Challenger was one of NASA’s greatest triumphs. It was the second shuttle to reach space, in April 1983, and successfully completed nine milestone missions before tragically exploding 73 seconds into its final flight.

Challenger infortunatley was also NASA’s darkest tragedy. On its 10th launch, on Jan. 28, 1986, the shuttle exploded 73 seconds after liftoff, killing its seven crew members. The tragedy changed the space program forever.

Space launches had become less than life-changing in the United States. Although the projected 50 launches per year did not materialize in the launch program, serving the Space Station and other somewhat mundane, non-moon landing level missions were not keeping the attention of the American public.

The launch on January 28, 1986, was different. The sun had been up for less than an hour and air temperatures were a few notches above freezing when the crew of STS-51L boarded the orbiter Challenger that Tuesday morning.

All around the United States and beyond people were excited—in large part because the seven-person crew’s included Payload Specialist Christa McAuliffe, a schoolteacher and mother of two chosen to fly as part of NASA’s Teacher in Space program. McAuliffe was proof that space was now truly open to average Americans, not just hot-shot astronauts. Students in school  nationwide would watch the launch LIVE and would truly know that no dream was beyond their reach in life.

Tragically, 73 seconds after Challenger’s launch, that dream quickly became a nightmare. Challenger disappeared as white vapor bloomed from the external tank. Spectators were stunned and instantly devastated. Teachers scrambled to get their kids out to recess and away from the reality of what had just taken place. And images of the horrific, Y-shaped explosion dominated the media cycle for days, weeks and months to come. For the first time in its history, NASA had lost its crew on a mission—with the nation watching on television.

Much has changed since that day in the space program, and the world we live in since the day Challenger exploded killing its entire crew, but our hearts still go out to the families and friends of those brave Americans. We firmly believe that the lessons learned from the terrible loss that day have been the foundation of what is and will always be a more safe and more transparent space program. You will forever stay in our hearts and minds Challenger… we thank you and we will never forget.

Sources: CNN, MSN, NASA