page_title: KH-9 Hexagon
section_title: Main camera
hierarchical_section_title: KH-9 Hexagon / Main camera
caption_attribution_description: English: Ground resolution of KH-9 HEXAGON's main camera system (trend as a function of mission number), with extrapolation of redacted data.
context_page_description: KH-9, commonly known as Big Bird or KeyHole-9, was a series of photographic reconnaissance satellites launched by the United States between 1971 and 1986. Of twenty launch attempts by the National Reconnaissance Office, all but one were successful. Photographic film aboard the KH-9 was sent back to Earth in recoverable film return capsules for processing and interpretation. The best ground resolution achieved by the main cameras was better than 0.6 metres.
  They are also officially known as the Broad Coverage Photo Reconnaissance satellites, built by Lockheed Corporation for the National Reconnaissance Office.
  The satellites were an important factor in determining Soviet military capabilities and in the acquisition of accurate intelligence for the formulation of U.S. national policy decisions as well as deployment of U.S. forces and weapon systems. The satellites were instrumental in U.S. National Technical Means of Verification of SALT and the Anti-Ballistic Missile Treaty.
  The KH-9 was declassified in September 2011 and an example was put on public display for a single day on 17 September 2011 in the parking lot of the Steven F.
context_section_description: The main camera system was designed by Perkin-Elmer to take stereo images, with a forward looking camera on the port side, and an aft looking camera on the starboard side. Images were taken at altitudes ranging from 90–200 miles (480,000–1,060,000 ft; 140–320 km). The camera optical layout is an f/3.0 folded Wright Camera, with a focal length of 60 in (1.5 m). The system aperture is defined by a 20 in (0.51 m) diameter aspheric corrector plate, which corrects the spherical aberration of the Wright design. In each of the cameras the ground image passes through the corrector plate to a 45-degree-angle flat mirror, which reflects the light to a 36-inch-diameter (0.91 m) concave main mirror. The main mirror directs the light through an opening in the flat mirror and through a four-element lens system onto the film platen. The cameras could scan contiguous areas up to 120 degrees wide, and achieved a ground resolution better than 2 ft (0.61 m) during the later phase of the project.
caption: A achieved ground resolution of Satellite Vehicles (SV) 1 to 18 main cameras.
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