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Harrison Jack Schmidt stares intently at the instruments of the Apollo 17 lunar landing module.

As the spacecraft named Challenger descends toward the moon, Jack calls out its altitude and speed.

Standing beside him in the cramped module is mission commander Gene Cernan.

His eyes are fixed on the window and his hands grip the controls.

Apollo 17 is moments away from landing on the moon.

Jack is the less experienced of the two astronauts. He's never been to space before.

In fact, unlike the other men who have made the journey here before him, he isn't even a pilot.

He's a geologist, and Jack hopes to become the first

scientist to land on the moon, but he and Gene have to get Challenger down safely first.

Their target is the Torres-Litro Valley. It's been chosen for its fascinating geology,

but it's a challenging place to land in. Drift off too far one way, and they risk crashing into a mountain.

Too far another, and they could end up in a giant crater.

The lunar lander weighs 16 tons, and is notoriously difficult to control.

Neil Armstrong overshot the Apollo 11 landing site by more than four miles,

and Jack knows if they do the same today, their mission

may be over before it begins. He and Gene have trained hard for this moment, though, and as

the moon looms ever larger outside their windows, both astronauts remain calm. In just 12 minutes,

they've traveled hundreds of miles and descended more than 35,000 feet out of

...