Scientific American 201907

(Rick Simeone) #1
540

600 feet

520

400
330

West Crater

Planned landing zone

The onboard
LPD (Landing
Point Desig­
nator) is steering
the lander
to ward a boulder
field north of
West Crater.

Armstrong assumes
attitude control of
the lander from the
onboard computer.

The Eagle approaches
the boulder field.

West Crater

Armstrong repositions (pitches
forward) the Eagle to maintain
ground speed and fly past the
boulder field.

The lunar lander flies over
the West Crater boulder field.

58 Scientific American, July 2019


THE FINAL MINUTES
The carefully choreographed mission hit a few snags as the
Eagle descended for landing. This map, created using the
same 3-D-modeling techniques as were used for the map on
the preceding pages, shows the lander’s altitude during the
nail-biting moments in which Armstrong navigated past
the intended landing spot—which turned out to be littered
with dangerous boulders—and found a new target literally
on the fly.
The trouble began at an altitude of about 33,000 feet,
when a warning light labeled “1202 program alarm” began
flashing on the Eagle’ s dashboard. “What is it?” Armstrong
asked Aldrin as the light blinked and a bell rang at irregular
intervals. Neither recognized the alarm from any of their
flight simulations. Eventually mission controllers radioed
that it could be safely ignored, but trying to determine its
cause wasted precious time.
As the lander’s fuel reserves dwindled, the Eagle became
increasingly difficult to maneuver. When the propellant in
its tank sank below 50 percent, the fuel started sloshing
wildly, jerking the vehicle in all directions. The issue also
caused the lander’s low-fuel-level alarm to go off between
30 to 45 seconds early, making it seem like the astronauts
had less time than they did to safely reach the ground.

Finally, with the Eagle at around 2,000 feet, Armstrong
looked out of his window to examine the proposed landing
site. (He should have done this several minutes earlier, but
as he said later in a debriefing, “our attention was directed
toward clearing the program alarms, keeping the machine
flying, and assuring ourselves that control was adequate to
continue without requiring an abort. Most of the attention
was directed inside the cockpit during this time.”) He didn’t
like what he saw. As he described it in the debriefing, the
landing site was a “large rocky crater surrounded with the
large boulder field with very large rocks covering a high
percentage of the surface.”
Running out of fuel and time, Armstrong took over steering
the spacecraft from the onboard computer at around 540
feet. Just under the wire, he guided the Eagle past the boulder
field to a safe landing on relatively flat ground.

Edward Bell is a contributing art director at
Scientific American and an animator specializing
in planetary science. He is author of the award-
winning iPad book Journey to the Exoplanets.
Free download pdf