The National Museum of the United States Air Force in Dayton, OH is home to some impressive aircraft. These include the famous B-17 bomber “Memphis Belle,” and the B-29 “Bockscar,” which dropped the atomic bomb on Nagasaki in 1945 to bring an end to the Second World War. The museum, which is the largest and oldest military aviation museum in the world, is spread over 19 acres and features an entire section of Cold War aircraft, missiles and photographic reconnaissance satellites.

Among those “eyes in the sky” is the KH-9, codenamed Hexagon but also known as the Big Bird. This series of satellites was the largest and last U.S. intelligence satellites to return photographic film to Earth. During the Cold War 19 HEXAGON missions imaged 877 million square miles of its surface between 1971 and 1986. The main purpose was wide-area search, which allowed analysts to pore over photos to focus in on potential threats with close-up surveillance from GAMBIT satellites.

The Invention of a Sky Satellite

The HEXAGON was first conceived in the early 1960s as a replacement for the CORONA reconnaissance satellites that were operated by the Central Intelligence Directorate of Science & Technology beginning in 1959. Much like the CORONA, the HEXAGON was developed to work in unison with the high resolution accuracy of the GAMBIT to identify high-value Soviet targets.

What is remarkable about the HEXAGON is that it utilized twin optical panoramic mirror cameras, which rotated and swept back and forth as the satellite flew over the Earth. This was a process that intelligence officials referred to as “mowing the lawn.” The cameras worked together to produce stereo images, taking overlapping images to form a very large panoramic view from above.

Images were taken at altitudes ranging from 90 to 200 miles. Each of the six-inch wide frames of HEXAGON film captured a swath of terrain that covered roughly 370 nautical miles on each pass over the Soviet Union and China. The cameras had a resolution of two to three feet.

Some of the missions included a separate mapping camera at the front of the satellite, which was able to capture a wider area that made for very accurate maps for war planning. The camera also featured its own bucket-like return vehicle.

The HEXAGON satellite missions lasted from 124 to 275 days and film was launched in four or five (for those with mapping missions) return capsules, which were caught mid-air by a Lockheed C-130 military aircraft snagging the capsules’ parachute. The film was brought to Hawaii and shipped to the CIA for analysis. However, the very first film bucket from a KH-9 HEXAGON sank to the bottom of the Pacific Ocean in early 1972 when the Air Force recovery aircraft was unsuccessful in snagging the bucket.

In total, the satellite carried about 20 miles of film that was originally 6.6-inches wide and about 2000ths of an inch thick and was only black and white. As technology improved the film did get thinner and eventually color, as well. Later missions carried as much as 30 miles of film.

The United States Force launched the HEXAGON satellites aboard Titan IIID rockets from Vandenberg AFB, CA, while tracking and control was conducted from Sunnyvale, CA.

Total Secrecy

Building the HEXAGON was no easy task, as its development included not only the satellite but also its very complex camera and film systems. The CIA played a role in designing the satellite, and envisioned that it would be 60-feet long, and weigh 30,000 pounds.

The Lockheed Corp. built the HEXAGON vehicle, and between 1966 and 1967 multiple contractors were selected to develop the subsystems. LMSC was awarded the contract for the Satellite Basic Assembly (SBA), Perkin-Elmer Corp. for the primary Subsystem (SS) that allowed the twin cameras to work together, McDonnell for the Reentry Vehicle (RV), RCA Astro-Electronics Division for the Film Take Up System, and Itek for the Stellar Index Camera (SI).

Throughout most of the HEXAGON’s use many of the individuals who worked on the various systems were unable to tell anyone what they did.

“One person who worked on the satellite told his wife and family he made dishwashers and other appliances,” said Douglas N. Lantry, Ph.D., curator and historian in the research division at the National Museum of the United States Air Force.

“Even when the project was fully declassified in 2011 it had been so secret that those who worked on it still didn’t know if they could talk to one another about it,” Lantry told ClearanceJobs.

Throughout the project there were several taboo words, and these included such terms as “optical bar” but not “HEXAGON.” Even when the teams did discuss the satellite, abbreviations were used and much of the talk was done in code – so that “LO” would describe the system’s film “looper” while “OB” was used for “optical bar.” Surprisingly the biggest taboo word was “film,” and that was because it would indicate that the HEXAGON was in fact an eye in the sky with a camera.

During phone conversations the use of code was strictly enforced, and anyone even saying a taboo work would require the other party to hang up. Moreover, when team members traveled they were required to leave identification and any identifying documents behind – and when signing in during a visit to another office those working on HEXAGON merely signed, “self.”

Down to Earth

From 1971 to 1986 there were 20 launch attempts of the HEXAGON by the National Reconnaissance Office (NRO), and 19 of those were successful. Ironically it was the final launch on April 18, 1986 that failed. That marked the end of the program, which cost a total of $3.262 billion (equivalent to $14.36 billion in 2018 dollars).

The program was declassified in September 2011, and an example of the HEXAGON satellite was put on public display for just a single day on September 17, 2011 in the parking lot of the National Air and Space Museum. Since January 26, 2012 the KH-9 HEXAGON has been on permanent loan from NRO at the National Museum of the United States Air Force. It is on display alongside its predecessors the KH-7 and KH-8.

While the museum houses numerous missiles, as well as the B-36 – the largest American bomber ever to take flight – and even a B-2 Spirit “stealth bomber” in its collection, the importance of the KH-9 HEXAGON can’t be understated. During the Cold War it was truly our eyes in the sky.