KH-8 Gambit 3 - Camera Optics Module

Camera Optics Module

The Camera Optics Module of KH-8 consists of four cameras.

The main camera of KH-8B (introduced in 1971) with a focal length of 175.6 in (4.46 m) is a single strip camera, designed to gather high-resolution images of ground targets. In the strip camera the ground image is reflected by a steerable flat mirror to a 1.21 m (48 in) diameter stationary concave primary mirror. The primary mirror reflects the light through an opening in the flat mirror and through a Ross corrector. At periapsis altitude of 75 nautical miles, the main camera imaged a 6.3 km wide ground swath on a 8.811 in (223.8 mm) wide moving portion of film through a small slit aperture, resulting in an image scale of 28 meter / millimeter. The Astro-Position Terrain Camera (APTC) contains three cameras: a 75mm focal length terrain frame camera, and two 90mm focal length stellar cameras. The terrain frame camera takes exposures of Earth in direction of the vehicle roll position for attitude determination. The stellar cameras observed in 180 degree opposite directions and took images of star fields.

The films used by GAMBIT were provided by Eastman Kodak, and evolved through a series of successively higher definition films, starting with Type 3404 with a resolving power of 50 to 100 line pairs per mm. Subsequent films used were Type 1414 high-definition film, SO-217 high-definition fine-grain film, and a series of films with silver-halide crystals of very uniform in size and shape. The size of silver-halide crystals decreased from 1,550 angstrom in film Type SO-315, to 1,200 angstrom in SO-312, and ultimately to 900 angstrom in SO-409.

Under optimal conditions GAMBIT would thus have been able to record ground features as small as 0.28 m to 0.56 m (1 ft to 2 ft) using the Eastman Kodak Type 3404 film. Using a film with a resolving power equivalent to the Kodak's Type 3409 film of 320 to 630 line pairs per mm, GAMBIT would have been able to record ground features as small as 5 cm to 10 cm (2" to 4") . The actual numbers of the ground resolution achieved by GAMBIT remain classified. GAMBIT was also able to record objects in orbit. The capability was developed to photograph Soviet spacecraft, but was first used to aid NASA engineers designing repairs for the damaged Skylab space station in 1973.