In May 1960, the Soviets shot down a U-2 spy plane over Soviet airspace. U-2s could fly at 70,000 feet (21.3km) but apparently, that wasn't high enough. We needed to go higher. To space!
So, the US needed a satellite that could take pictures! The thing is, a U-2 flight eventually lands-- the film in the cameras could be taken out and developed. If we launch a satellite, we needed a way to get the film from space to intelligence officers. This had never been done before.
They worked for years but eventually the CIA launched the U.S.'s first spy satellite, CORONA. CORONA's first on-board camera was five feet long, and could see things about 40 feet across. It was America's first imaging satellite, and also the first U.S. satellite program, ever.
Since it used film, CORONA would take pictures, and drop the film in heavy buckets with parachutes. The buckets would reenter the atmosphere, and be caught by a "claw hook" hanging off military cargo planes, or recovered by ships after splashdown.
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