KH-9 (BYEMAN codename HEXAGON), commonly known as Big Bird or KeyHole-9,^[1] was a series of photographic reconnaissance satellites launched by the United States between 1971 and 1986. Of twenty launch attempts by the National Reconnaissance Office, all but one were successful.^[2] Photographic film aboard the KH-9 was sent back to Earth in recoverable film return capsules for processing and interpretation. The highest ground resolution achieved by the main cameras of the satellite was 2 ft (0.61 m),^[3] though another source says "images in the "better-than-one-foot" category" for the last "Gambit" missions.^[4]

They are also officially known as the Broad Coverage Photo Reconnaissance satellites (Code 467), built by Lockheed Corporation for the National Reconnaissance Office (NRO).^[1]

The satellites were an important factor in determining Soviet military capabilities and in the acquisition of accurate intelligence for the formulation of U.S. national policy decisions as well as deployment of U.S. forces and weapon systems. The satellites were instrumental in U.S. National Technical Means of Verification of Strategic Arms Limitation Talks (SALT) and the Anti-Ballistic Missile Treaty (ABMT).^[5]

The KH-9 was declassified in September 2011 and an example was put on public display for a single day on 17 September 2011 in the parking lot of the Steven F. Udvar-Hazy Center of the National Air and Space Museum.^[6][7][8]

On 26 January 2012, the National Museum of the United States Air Force put a KH-9 on public display along with its predecessors the KH-7 and KH-8.^[9]

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. Lockheed Missiles and Space Company (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) were completed in May 1971, and it was subsequently shipped to Vandenberg Air Force Base in a 70 ft (21 m) container. Ultimately, four generations ("blocks") of KH-9 HEXAGON reconnaissance satellites were developed. KH9-7 (missions 7 to 12) was the first to fly a Block-II panoramic camera and SBA. Block-III (missions 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 (missions 19 and 20) was equipped with an extended command system using plated-wire memory.^[10] In the mid 1970s, over 1,000 people in the Danbury, Connecticut area worked on the secret project.^[11]

A reentry vehicle from the first Hexagon satellite sank to 16,000 ft (4,900 m) 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 had disintegrated during the nine months underwater, leaving no usable photographs.^[12]

Over the duration of the program, the lifetime of the individual satellites increased steadily. The final KH-9 operated for 275 days. The satellite mass with and without the Mapping Camera System was 13,300 and 11,400 kg (29,300 and 25,100 lb), respectively.

(NSSDC ID Numbers: See COSPAR)

The total cost of the 20 flights KH-9 program from FY1966 to FY1986 was US$3.262 billion in respective year dollars (equivalent to 17.47 billion in 2023, with an average reference year of 1976).^[10]

Data source: The Encyclopedia of US Spacecraft ^[1] and NSSDC

• Launch vehicle: Titan IIID/34D
• Total weight: 11,400 kg (25,100 lb), with mapping camera 13,300 kg (29,300 lb)
• Reentry weight: 5,330 kg (11,750 lb) ^[54]
• Max. diameter (main body): 3.05 m (10.0 ft) ^[54]
• Length (with mapping camera): 16.21 m (53.2 ft)^[54]
• Orbit: elliptical, 160 km × 240 km (99 mi × 149 mi)
• Scanners: television, radio, and high resolution camera

• The reaction control system of a KH-9, showing the propellant tanks.
• A KH-9 in scaffolding, being prepared for launch.
• A technician despools one of the re-entry modules which contained the film used by the cameras.
• A diagram showing the assembly, testing and launch preparations of a KH-9.
• The forward section of a KH-9.
• A KH-9 re-entry module hanging from its parachute, ready to be retrieved.
• Another view of the KH-9's reaction control system.
• A KH-9 being transported by truck in a special canister.
• The shroud and base of a KH-9 undergo vibration tests in an acoustic chamber.
• This painting of a KH-9 shows the two different camera types that the satellite carried.
• Basic specifications and diagram of the KH-9.
• This diagram shows the various sections of the KH-9 and their dimensions.
• A KH-9 at the National Museum of the United States Air Force (front view).
• A KH-9 at the National Museum of the United States Air Force (forward section).
• A KH-9 at the National Museum of the United States Air Force (film recovery unit).
• A KH-9 at the National Museum of the United States Air Force (center section).
• A KH-9 at the National Museum of the United States Air Force (left camera).
• A KH-9 at the National Museum of the United States Air Force (rear view without solar panels).

Other U.S. imaging spy satellites:

• CORONA series:
  • KH-1
  • KH-2
  • KH-3
  • KH-4
• KH-5 Argon
• KH-6 Lanyard
• KH-7 Gambit
• KH-8 Gambit 3
• KH-10 (Manned Orbiting Laboratory)
• KH-11 Kennen
• KH-13 (Enhanced Imaging System)