The CIA declassified portions of it’s KH-9 Hexagon imaging satellite in 2011. Hexagon was first deployed into space in 1971. Between 1977 and 1986 Hexagon performed 19 missions, imaging 877 million square miles of the Earth’s surface. The KH-9 was also the last and largest imaging satellite to return it’s photographic film to earth.
Hexagon was desgined to replace the Corona series imaging spacecraft:
The KH-9 was originally conceived in the early 1960s as a replacement for the Corona search satellites. The goal was to search large areas of the earth with a medium resolution camera. The KH-9 carried two main cameras, although a mapping camera was also carried on several missions. The photographic film from the cameras was sent to recoverable re-entry vehicles and returned to Earth, where the capsules were caught in mid-air by an aircraft. Four re-entry vehicles were carried on most missions, with a fifth added for missions that included a mapping camera.
Between September 1966 and July 1967, the contractors for the Hexagon subsystems were selected. LMSC was awarded the contract for the Satellite Basic Assembly (SBA), Perkin Elmer for the primary Sensor Subsystem (SS), McDonnell for the Reentry Vehicle (RV), RCA Astro-Electronics Division for the Film Take Up system, and Itek for the Stellar Index camera (SI). Integration and ground-testing of Satellite Vehicle 1 (SV-1) was completed in May 1971, and it was subsequently shipped to Vandenberg Air Force Base in a 70 ft container. Ultimately, four generations (“blocks”) of KH-9 Hexagon reconnaissance satellites were developed. KH9-7 (1207) was the first to fly a Block-II panoramic camera and SBA. Block-III (vehicles 13 to 18) included upgrades to electrical distribution and batteries. Two added tanks with ullage control for the Orbit Adjust System (OAS) and new thrusters for the Reaction Control System (RCS) served to increase KH-9’s operational lifetime. In addition the nitrogen supply for the film transport system and the camera vessel was increased. Block-IV was equipped with an extended command system using plated wire memory. In the mid 1970s, over 1000 people in the Danbury, Connecticut area worked on the secret project.
A reentry vehicle from the first Hexagon satellite sank to 16,000 feet below the Pacific Ocean after its parachute failed. The USS Trieste II (DSV-1) retrieved its payload in April 1972 after a lengthy search but the film disintegrated due to the nine months underwater, leaving no usable photographs.
Over the duration of the program the lifetime of the individual satellites increased steadily. The final KH-9 operated for up to 275 days. Different versions of the satellite varied in mass; most weighed 11,400 kg or 13,300 kg.
I suggest going through the Hexagon Wikipedia page as is there are some very interesting photos of the different components of the spacecraft.
In 2013, Phil Pressel wrote the definitive guide to Hexagon called: Meeting the Challenge: The Hexagon Reconnaissance Satellite. From the Amazon book description;
Meeting the Challenge: The Hexagon Reconnaissance Satellite is the recently declassified story of the design, development, production, and operation of the Hexagon KH-9 reconnaissance satellite. It provided invaluable photographic intelligence to the United States government, and it stands as one of the most complicated systems ever put into space. In 1965 CIA Director John McCone issued the call for a satellite with unparalleled technical requirements that could visually map most of the landmass of the earth, photograph selected areas of interest, and return the resulting film safely to Earth. Developed by the Perkin-Elmer Corporation and operated between 1971 and 1986 Hexagon was the last film-based orbiting photo-reconnaissance satellite. This engineering marvel features the following achievements: the world’s largest spherical thermal vacuum chamber used to test the system; the development and use of new and sophisticated electronics, such as LED’s and brushless motors; the ability to precisely control the synchronization of film traveling at up to 200 inches per second at the focal plane, on a rotating camera, mounted in a moving vehicle and focused on a moving earth; sixty miles of film used on each mission; and, stereo photography of the entire surface of the earth. When film captured by the satellite was sent back to earth it launched in a film-return capsule which was snagged by an aircraft as it parachuted downward upon reentering the earth’s atmosphere. In 1972 a film bucket containing sensitive images sank to the bottom of the Pacific Ocean, resulting in a daring rescue three miles underwater by the U.S. Navy’s submergence vehicle Trieste II. Featuring both technical details and historical anecdotes, former Perkin-Elmer engineer Phil Pressel has written the definitive account of this important chapter in U.S. intelligence and aerospace history.
Seems like an interesting book and as such Mr. Pressel has done quite a few media interviews. I recently watched this one from the International Spy Museum in Washington DC:
As Mr. Pressel mentioned in the interview, you can view the KH-9 Hexagon at the National Museum of the USAF. I do recall seeing it there but being rather time limited I didn’t quite have an appreciation for exactly what I was looking at. I look at the satellite with a guide and to our amusement we noticed a piece of plywood acting as a bracing member on the airframe (granted the KH-9 there is a “mockup” used to troubleshoot problems the real satellites may be having in space).