7 years ago
These Concrete Relics in Arizona Helped Satellites Spy on the Soviets
Venture into the Sonoran Desert about an hour south of Phoenix and you’ll eventually stumble upon a concrete cross. More than 100 dot the terrain, each of them 60 feet across and spaced precisely one mile apart. The government used them to calibrate the world’s first spy satellites as they peered down on Russia and China while photographing more than 750 million square miles of the planet.
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https://www.wired.com
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