40 years ago today, the Challenger space shuttle exploded on live television just 73 seconds

after liftoff. All seven astronauts aboard died, including Krista McCullough, the first teacher,

an ordinary citizen to fly in space, plunging the nation into morning.

I spoke with our science correspondent, Miles O'Brien, who has covered the space program for decades,

about that moment and how it changed the country for our video podcast, Settle in. Here's some of that

conversation. Why was this particular launch? Why did it capture the public's imagination in a way that

previous launches hadn't? It was all about the teacher, Jeff, Krista McCullough, elementary school teacher from Concord,

New Hampshire, who had participated in a nationwide contest to become the first teacher in space.

She was a fabulous, interesting character and won the rights to fly on the shuttle

as the shuttle program turned toward allowing civilians to fly in space. And they were leaning

toward trying to show the world that the space shuttle system was routine and could get people to space,

everyday people to space in a relatively inexpensive way.

In 1986, they had 15 flights on the manifest, way, way beyond anything it had attempted in the past.

It was going to launch spy satellites, commercial satellites, scientific missions,

and they were really kind of hell-bent to prove that this system was reliable enough

for a teacher to fly and give lessons.

And so the world was fixated on that after 24 previous flights.

The first flight, of course, in 1981 got a lot of attention.

The shuttle has cleared the tower.

Then many of the flights fell off the front page of the newspapers.

But this one really captured hearts and minds and pointedly, sadly, was watched by hundreds of thousands of school kids in their classrooms that morning.

You happened to be there that day. Set the scene for us. What was it like? Well, I wasn't quite there.

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