http://www.thespacereview.com/article/2013/1The geometry of shadows
by Dwayne A. Day
Monday, January 30, 2012
On September 19, 1968, GAMBIT mission 4316 sailed high over the arid Kazakh steppes. The GAMBIT 3—known as the KH-8 to the community that used its products—was a long, thin spacecraft, looking something like a pencil. Inside, the finest in American optics, manufactured by Kodak, stared down at the ground below. Those optics focused on a marvel of modern chemistry, a film, also manufactured by Kodak, that had an incredibly fine grain so that it could capture as much of the image that shown on it as possible as the film moved past a thin slit on the focal plane. That film could be enlarged many times on print, although the hard analysis was done on film positives spread over a light table in a windowless building at the edge of the Washington, DC, Navy Yard, where photo-interpreters stared at panchromatic images and measured shadows and applied basic geometry to determine the heights of objects.
On this September day the Americans got lucky. The skies over the primary Soviet rocket and missile test facility were clear. And down at Tyura-Tam, as it was then known, the Soviets were doing something very interesting. They had rolled out their Moon rocket, a giant vehicle as tall as a Saturn V. It occupied one of their two triad-shaped launch pads. The Americans photographed it at incredibly high resolution. The CIA labeled this the “J vehicle” because they had designated its launch facility at Tyura-Tam as “Complex J” (the Sputnik launch pad, the first identified by the CIA in U-2 overflights, had been designated Complex A). Much later western analysts came to know it as the N-1.