Today, we expect the unexpected. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
"How high is the sky?" asks
Donald Hunton, an Air Force physicist. Airplanes
can still fly 12 miles up. But the air is only a
20th as thick as it is on the ground. The space
shuttle orbits at altitudes 15 times higher than
that -- 170 miles up. Strange things happen to the
air that's left at those heights.
For one thing, the air is one ten-billionth as
thick as it is down here. It's so thin that
molecules can easily travel miles without hitting
another molecule. And those molecules are hotter
than the ones around us -- over 1000x F -- but
there aren't enough of them to heat anything. The
air's too thin. It's composition is odd because
lightweight molecules and hot molecules float to
the top of the atmosphere. There's a lot more
hydrogen and helium up there.
That high-altitude air is giving space engineers
fits. Down on earth's surface we're protected from
heavy ultraviolet radiation. At high altitudes that
radiation breaks diatomic oxygen into atoms. And
high-temperature atomic oxygen is viciously
corrosive stuff.
So unexpected problems arise. The first symptom
astronauts saw was a glowing corona around surfaces
facing into what we might call "the wind." It's not
a kind of wind you can feel. The air's too thin for
that. But it reveals itself in a glowing shock wave
around the shuttle. The glow is caused by
complicated chemical reactions, and those reactions
are made worse by the high speed. The shuttle moves
so fast that it breaks certain molecules apart when
it hits them.
Worse than that, atomic oxygen attacks many
surfaces. The shuttle returns to earth with camera
lenses fogged, with clear plastic covers turned
yellow, and with paint dulled.
Research is now aimed at inventing materials that
won't be affected by atomic oxygen. Space engineers
are especially worried about the Hubble space
telescope. It's scheduled to fly in 1990, and
they've found the coating designed to protect its
lens will trigger a bright corona. Any corona will
blind the telescope as it squints into the inky
reaches of space.
But don't worry. The Hubble telescope will fly.
Engineering designers expect the unexpected.
They're at their best when they have to slip the
clutches of problems from their blind side. A new
material, an altered configuration, a new concept
-- it's fun, I tell you. It's so much fun to beat
nature at her own game.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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