Critical to US Security: The Development of the Gambit and Hexagon Satellite Reconnaissance Systems [open pdf - 3MB]
From the Introduction: "Since the early 1960s, US policymakers have come to rely increasingly on photo-reconnaissance satellite imagery for timely and accurate intelligence. Photo-reconnaissance satellites and the information they provide have become virtually indispensable to the US Intelligence Community and its intelligence assessments. Developed, operated, and managed by the National Reconnaissance Office (NRO) , these satellite systems sparked a revolution in intelligence collection. Operating in a crisis atmosphere, the NRO forged a unique working partnership with US private industry to design and build these new satellite systems. The NRO/industry partnership drove space reconnaissance technology beyond current limits. It made possible a new generation of photo-reconnaissance technologies that resulted in the acquisition of never-before-seen, detailed intelligence data for US officials."
Government Publishing Office: http://www.gpo.gov/