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The National Reconnaissance Office envisioned using the shuttle to carry cameras that would image large parts of the Soviet Union over the course of each mission. (credit: NASA)

Black ZEUS: The top secret shuttle mission that never flew

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In the late 1970s, the secret National Reconnaissance Office (NRO), which developed and operated the United States’ fleet of intelligence satellites, began studying a top secret payload that would fly inside the Space Shuttle’s payload bay. The payload, named ZEUS, would have featured a pair of powerful reconnaissance cameras capable of observing large portions of the Soviet Union during a shuttle flight. One variant of ZEUS would have been a recoverable “free-flyer” satellite, deployed by the shuttle and retrieved by a later shuttle mission. ZEUS was so secret that not even its existence was acknowledged—blacker than black, as the spooks would say. But now, recently declassified documents have shed light on this top secret, almost completely unknown shuttle payload.

The payload, named ZEUS, would have featured a pair of powerful reconnaissance cameras capable of observing large portions of the Soviet Union during a shuttle flight.

Throughout the 1970s NASA was building the Space Shuttle, and other American space agencies looked toward its debut with varying degrees of hope, skepticism, and even hostility. The Air Force planned on retiring its fleet of expendable launch vehicles and transitioning numerous satellites including missile warning satellites, comsats, weather satellites, and Navstar GPS satellites to fly on the space shuttle by the mid-1980s. NRO leadership was less enthusiastic about the shuttle than some in the Air Force, both because of concern that an accident could ground the shuttle for an extended period of time, and the requirement for secrecy for their intelligence satellites. Every shuttle launch would get attention, and the spooks hated attention.

NRO Director Hans Mark ran the secret reconnaissance satellite organization from 1977 until October 1979. Mark was promoted to Secretary of the Air Force in July 1979 and gave up the NRO hat a few months later. In his 1987 memoir, Mark recounted that he had pushed the reluctant NRO organization to move its satellites to the space shuttle and take advantage of its unique capabilities (see “The spooks and the turkey”, The Space Review, November 20, 2006). ZEUS was probably a major aspect of this policy change.

ZEUS concepts
Artist illustration of various configurations of HEXAGON cameras carried in the shuttle bay. It is unclear if these are concepts for ZEUS or an electro-optical version of the camera system that would store the imagery electronically. Considering the state of data storage technology in the 1980s and the massive amount of data that could be captured by the HEXAGON optics, a digital system would have stressed the state of the art.

The dawn of ZEUS

The existence of ZEUS was disclosed in Jeffrey Richelson’s 1990 book America’s Secret Eyes in Space. Richelson described ZEUS and another project known as DAMIEN as shuttle-based camera systems studied by the NRO. But until now little was known about either system. A newly declassified 1979 document explains that “Project ZEUS is intended to be the photographic space program which will replace Program 467, satisfy standing search and Mapping, Charting and Geodesy requirements of the mid-1980s and beyond, provide the flexibility and capability of a film system, provide inherent responsiveness, and achieve low life-cycle cost.” Program 467 was another term for the HEXAGON reconnaissance satellite, a school bus-sized spacecraft that entered service in 1971 and operated until the mid-1980s. HEXAGON played an important role in the space shuttle program. When NASA was first designing the shuttle, they sought the backing of the national security community, including the NRO, which lent its support to the shuttle in return for NASA agreeing to size its payload bay to be big enough to carry a HEXAGON.

Although film seems like an ancient and outdated technology today, it was a powerful data storage method. Film was tremendously effective for taking photographs of large amounts of territory at relatively high resolution.

HEXAGON is considered by many people who worked on it at the time to be the most-sophisticated mechanical spacecraft ever flown. That is because it was a film-based camera system that ran strips of film at very high speed through two rotating cameras that swept a large field of view beneath them, covering the distance of Cincinnati to Washington, DC in a single image. It was also complicated because the camera reduced image smear despite the high-power optics, camera rotation, and the speed of the film. The film was collected in four Satellite Recovery Vehicles (SRVs) that were returned to Earth as they filled up. Later on, a separate mapping camera was added to the front of the satellite and equipped with its own smaller SRV.

Although film seems like an ancient and outdated technology today, it was a powerful data storage method. Film was tremendously effective for taking photographs of large amounts of territory at relatively high resolution. Although the exact resolution of the HEXAGON system remains classified, it was considerably better than the officially-stated capability of 0.6 to 1 meters. In fact, a person using a relatively simple formula and plugging in the known parameters of the HEXAGON system can develop their own estimate of its capabilities: about 0.2 meters at nadir (looking straight down) from perigee, and 0.4 from apogee. Of course, the imagery included angles considerably away from nadir, so the stated figures may be reasonably close to an average or “typical” value. It was the combination of resolving power and area coverage that made the HEXAGON so impressive.

HEXAGON was launched atop Titan 34D rockets throughout the 1970s, and at various times the National Reconnaissance Office considered shifting the HEXAGON to the space shuttle when the shuttle began flying, starting with the twenty-first HEXAGON vehicle. The original launch date for the shuttle was 1979, but that eventually slipped to 1981. The NRO studied multiple variants of the HEXAGON, including some with more film-return capsules and even radically different designs for shuttle launch. They also studied options for recovering HEXAGON satellites after their film was expended. For reasons that are still unclear, NRO officials decided against flying the HEXAGON on the shuttle and halted production of the satellites at twenty vehicles.

By the late 1970s, the NRO was considering ending HEXAGON but using its optical system—the two powerful rotating cameras—in a new system that would take advantage of the shuttle’s planned reusability. “The ZEUS system will be STS optimized for launch economics, recovery and recycle, and payload vs. STS parameters,” the declassified NRO document states. “The photographic hardware will utilize current technology in electronics, computers, software, and structural materials.” By 1979, the objectives and requirements for ZEUS were known, technical feasibility had been established through studies, but no hardware solutions had been selected.

The hardware designs being studied included palletized and free-flyer options. At the time, NASA and its potential user community expected that the shuttle would fly frequently, even weekly, and NASA was evaluating common systems that would be carried in the shuttle payload bay that could support different payloads. The palletized ZEUS option would be a fully integrated system, and it could use the onboard processing capabilities of the shuttle orbiter. It might also be equipped with a real-time or near-real-time system so that an operator inside the orbiter could maximize the performance of the camera system. The NRO anticipated that ZEUS would fly on 21-day shuttle missions, but acknowledged that the on-orbit lifetime of the shuttle orbiters had still not been determined.

Another option that the NRO was studying for ZEUS was a free-flyer version. This would be launched from the shuttle, released into orbit, and then be retrieved by a later shuttle flight and returned to Earth for refurbishment. Even by the late 1970s NASA was expecting dozens of shuttle flights per year—up to 50 at one point—and so NRO officials considered routine deployment and recovery of ZEUS to be entirely feasible.

KENNEN demonstrated that the era of film-return satellites, which had started in the late 1950s, was coming to an end. KENNEN was undoubtedly one of the reasons why the NRO did not develop ZEUS.

In either configuration, ZEUS would operate in a standard shuttle orbit of 120–160 nautical miles (220–295 kilometers), which was higher than a typical HEXAGON orbit. This meant that even though ZEUS would have the same 60-inch (1.5-meter) focal length optical system as HEXAGON, the images it produced would be lower resolution than the HEXAGON. The shuttle would launch from either Florida into 57-degree inclined orbits, or 96-degree inclined orbits flying from Vandenberg Air Force Base in California. The NRO’s plan in 1979 was for up to four palletized launches in 1984, increasing to a maximum of six palletized launches a year starting in 1985. But the projected launch schedule was two per year from Florida and one per year from Vandenberg, starting in 1985.

In addition to the film-based ZEUS system, it also appears that the NRO considered using the HEXAGON cameras in an electro-optical configuration, substituting an early CCD array for the film. A declassified image shows several configuration concepts featuring the long optical bar HEXAGON optics, but no film supplies. Phil Pressel, who designed the original HEXAGON camera system in the latter 1960s while at Perkin-Elmer Corporation in Danbury, Connecticut, referred to these illustrations as highly dubious and doubts that whoever drew them understood the HEXAGON system. Pressel, whose 2013 book Meeting the Challenge describes the development of the HEXAGON camera, said he would need to see more to understand what was being proposed for these palletized shuttle payloads. But Pressel acknowledged that there were multiple studies of flying HEXAGON optics inside the space shuttle’s payload bay.

The demise of ZEUS

In December 1976, the Air Force launched the NRO’s first KH-11 KENNEN satellite. KENNEN used an electro-optical system that turned images into digital data that was then beamed back to a ground station. A second KENNEN was launched in 1978. Both spacecraft suffered some problems and had some limitations, such as a smaller field of view than HEXAGON or ZEUS. But, they demonstrated that the era of film-return satellites, which had started in the late 1950s, was coming to an end. KENNEN was undoubtedly one of the reasons why the NRO did not develop ZEUS. Although KENNEN could not image the vast amounts of territory that each HEXAGON mission could, KENNEN stayed aloft for years, constantly beaming down data, whereas the maximum life of a HEXAGON satellite was nine months—when the film ran out, the satellite was useless.

Another likely reason for the cancellation of the ZEUS program was Hans Mark’s departure from the NRO. Without a strong shuttle advocate at the helm, the NRO rank-and-file, and eventually its new leadership, began strongly resisting the policy requiring that they launch their payloads on the space shuttle. ZEUS may have offered capabilities required by the American intelligence community, but that was insufficient to prevent it from being canceled. Within only a few years, the NRO began moving every satellite that it could off of the shuttle and back to expendable rockets. That move did not happen as fast as some at the NRO would like, and when the Challenger came apart in a cold Florida sky in January 1986, a number of NRO satellites were left on the ground without a path to orbit. ZEUS, however, was not one of them.