As they descend to the surface of the Moon during the final 13 minutes before landing,

Neil Armstrong and Buzz Aldrin are in their spacesuits, visors down.

They are in their ramps cabin, in an atmosphere of pure oxygen.

The Apollo spacecraft's life support systems were a critical link in the chain of survival

for the astronauts.

Failures here could lead to deadly consequences, something NASA discovered at terrible

cost in January 1967.

Here's Neil Armstrong talking in 2001 with some emotion about the darkest moment in

the Apollo program, the disaster that struck Apollo 1, a fire in pure oxygen during testing

of the command module capsule on the grounds of the launch pad in Florida, a catastrophe

that killed his astronaut colleagues, Gus Grism, Roger Chaffey and Ed White.

Ed White and I were good friends, neighbors, very traumatic times.

You're much more likely to accept loss of a friend in flight, but it really hurt to lose

a minute ground test and that was indictment of ourselves.

We didn't do the right thing somehow.

That's doubly traumatic.

We choose to go to the moon.

Captain, we're go for landing.

He'll get to hear us go for landing, over.

We're getting on the 12th floor through the program alarm.

Hold it at 18 foot, we're going to make it a thing.

Roger.

...