Everywhere you look in aerospace, you'll find composites.
by Mark Clarkson
ATK Aerospace Systems builds composite space structures, including solid rocket boosters for the shuttle, rocket motor cases and nozzles. Its commercial launch vehicle, Liberty, is expected to launch next year. When it comes to building for space, designs are cut to the bone, asserts Nathan Christensen, ATK's senior manager, engineering tools and analysis.
"In space vehicles," he says, "you have very low margins of safety. They're designed right down to the gnat's eyeball. An unmanned vehicle might have a safety margin of 1.2. A manned vehicle might still only have a 1.5 margin, whereas with an aircraft you're looking at margins of 4 or 5."
Unlike metals, composites fail progressively. Cracks or delaminations in one area redistribute stresses to adjoining areas, which fail in turn.
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