Beginning with Discoverer 14, each Corona program satellite carried increasingly sophisticated camera equipment on-board. They used special 70mm film made by Kodak (for the sake of comparison, civilian cameras typically use 35mm film) which allowed for wide and high resolution shots. Early Corona satellites carried about a mile and a half of film for each of the two cameras on board
To calibrate the cameras from space, the Air Force made a giant grid of concrete crosses in the desert outside of Phoenix, Arizona. These 267 crosses, each about 60 feet in diameter, are a mile apart from one another down to the millimeter. They were used as "ground truth" targets
The problem, of course, was how to recover the precious photographic intelligence
The solution was to jettison the two re-entry capsules for each camera (appropriately known as the "film buckets"). These each came equipped with a heat shield which would be dropped after the film bucket reached 60,000 feet, at which point a parachute would be deployed. The film bucket would continue its descent to Earth until about 15,000 feet, at which point a plane would fly by and scoop the descending capsule out of the air. While such a recovery technique might seem delightfully analog today, China was using film buckets as recently as 2005 for their surveillance satellites.
Thursday, June 20, 2019
"The First Spy Satellites Had to Drop Gigantic Buckets of Film Back to Earth"
Vice (from 2017):