Drawing showing the side-by-side arrangement of HEXAGON’s twin rotating KH-9 panoramic cameras. You can see both cameras on the underside of the satellite. (Photo courtesy of National Reconnaissance Office)
This drawing shows the extremely complex path of HEXAGON KH-9 main camera film. It ran through more than 100 rollers and precision “air bar” assemblies where it floated on a cushion of gas. The feed reels are on the right, and the four return capsules are on the left, with the cameras in the middle. Film moved at up to 200 inches per second inside the airtight, light-tight, pressurized, climate-controlled film path. (Photo courtesy of National Reconnaissance Office)
HEXAGON KH-9 reconnaissance satellites were the largest and last US intelligence satellites to return photographic film to earth. HEXAGON provided vital intelligence and mapping photos from space that allowed US planners to counter Cold War threats. Between 1971 and 1986, 19 HEXAGON missions imaged 877 million square miles of the earth's surface.
The HEXAGON system improved upon the earlier CORONA satellites. Like CORONA, HEXAGON's main purpose was wide-area search, as opposed to close-up detail imaging like the GAMBIT satellites. Analysts could search broad and wide areas for threats with HEXAGON, then focus in on suspect areas with surveillance from GAMBIT satellites. Used together, these systems proved very effective.
The Lockheed Corp. built the basic HEXAGON vehicle. Its development included creating very complex cameras and film systems. The panoramic cameras, designated KH-9 and made by Perkin-Elmer, were two-part devices. Two separate cameras could work together to produce stereo images. Both cameras used a "folded path" to bend and focus light in a tight space using special mirrors and lenses to produce sharper photos.
The so-called "optical bar cameras" spun on their axes, each taking a long strip image perpendicular to the satellite's forward direction. Each successive strip overlapped a little, creating a very large panoramic picture. Objects smaller than 2 feet across could be imaged from around 80-100 miles altitude.
The Air Force launched HEXAGON KH-9 satellites aboard Titan IIID rockets from Vandenberg AFB, Calif., and provided tracking and control at an Air Force facility at Sunnyvale, Calif.. USAF aircraft recovered film capsules in midair near Hawaii.
Altitude: 80-370 nautical miles Mission duration: 124 days average Panoramic camera: Perkin-Elmer, f/3.0, focal length 60 in., aperture 20 in. Film: 320,000 ft. (60 miles) long, 6.6 in. wide Image resolution: Better than 2-3 ft. Film return capsules: 4 Payload weight: 7,375 lbs.