"Too many of us buy sunglasses on impulse, let's say at an airport, " he says.

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Its creators say the Solar Impulse is designed to showcase the potential of solar power and will never replace fuel-powered commercial flights.

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Americans have a strong impulse for course corrections and a sense that their greatness could be lost, but let's say for argument's sake that the U.S. is a declining superpower along the lines of postwar Britain.

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