The Space Review

protruding shroud
The eleventh heavy ferret satellite. Note the odd protrusion on the side of the payload fairing. (credit: Paul Gatherer)

Ferrets of the high frontier: US Air Force ferret and heavy ferret satellites of the Cold War

<< page 1: the Agena ferrets


A total of sixteen of these Agena ferret satellites were launched atop Thor boosters between February 21, 1962 and July 16, 1971. Photographs of the first fifteen launches have become available, although there is no photograph of the payload section of the fourteenth launch. It is now clear from photographs of various payload shrouds for these spacecraft that they underwent several changes over the years.

Photographs of the first four Agena ferret launches all show a vehicle with a relatively small, pointy launch shroud, often obscured by an inflatable air conditioning blanket while on the launch pad. Photographs of the fifth and later vehicles show a subtle change, the addition of a cylindrical section above the Agena and below the conical nose cover. This is consistent with previous documentation indicating that only four of the F-2 satellites were built and that a follow-on F-3 was planned.

It is now clear from photographs of various payload shrouds for these spacecraft that they underwent several changes over the years.

A photo of the eleventh launch vehicle, which was launched on July 25, 1967 under the designation Program 770, shows a large protrusion on the side of the shroud. This indicates some kind of change in the payload. No protrusion is visible on two available photos of the twelfth launch, although they were taken from different angles than the photos of the eleventh launch. It therefore appears as if the eleventh Agena ferret carried some specialized equipment not carried on other vehicles.

Photographs of the thirteenth and fifteenth Agena ferret launches, dated October 5, 1968 and August 26, 1970 respectively, depict much larger launch shrouds than used for the earlier launch vehicles. This strongly implies another significant change in the satellite payload.

No photographs of the payload shroud for the fourteenth or sixteenth launch vehicles are yet available for comparison. It is therefore not yet possible to determine if the larger payload shroud was also used for these two launches. But these photos now suggest that the Agena ferret program included at least four, and possibly five variants. These are:

F-2/Program 102/Program 698BK1-4
F-3?/Program 698BK5-7
Program 7708-10, 12
Program 770 (with protrusion)11
larger shroud13, 14?, 15, 16?

The specific mission of the Agena ferrets remains unknown, but they obviously were larger and had greater pointing/stability and power requirements than their ferret subsatellite counterparts. The Agena spacecraft that placed them in orbit also provided power and stabilization.

The fact that these satellites remained in production through 1970, even after the introduction of the more numerous ferret subsatellites, indicates that they served some unique role. However, they were discontinued soon after the CANYON high-altitude comint satellites entered service, which might imply that the primary value of the Agena ferrets was for communications intelligence gathering and not general monitoring of radar signals. Planned comint collection via satellite is mentioned in still-classified documents as early as April and May 1962, and was apparently part of the dispute that resulted in Admiral Frost’s firing from the NSA.

The major problem with such a conclusion, however, is that low Earth orbit is a poor place to conduct communications intelligence interception, for the satellite quickly moves out of range of the communications signals. An Agena ferret gliding overhead with its nose-mounted antennas pointed down at the ground might receive only the boring parts of conversations, or nothing at all. It is like trying to listen to an important conversation two people are having on a street corner while you pass by on a bicycle.

CANYON, which flew in a much higher orbit that appeared to trace a figure-eight pattern in the sky, was much better suited to intercepting communications between Soviet microwave communications towers. The Soviet Union had a large network of microwave communications towers and microwave beams transmitted from one tower to another would leak out into space, where they could be intercepted by a satellite that crossed through the beam. The Agena ferrets would not have been very useful for this kind of mission, although their operations may have initially identified the vulnerability of Soviet microwave communications to interception in orbit. The KH-7 GAMBIT photo-reconnaissance satellite was ultimately used to determine the precise line-of-sight of these multiple microwave towers. This certainly enabled analysts to determine the layout of the Soviet communications net, but also enabled them to determine the points in space where the microwave transmissions would be most vulnerable to interception.

According to Robert Naka, the former Deputy Director of the National Reconnaissance Office, there were other drawbacks to operating sigint satellites in low orbits besides their short time over their targets. “What we generally did was we put a tape recorder in the satellite and tried to store the signals until we came over one of our U.S. based control stations, when we dumped out the signals tape from the tape recorder,” Naka said during an interview in 2000. “Well, the tape was a very fragile unreliable thing. We began to learn how to make that go a whole lot better,” he explained. “The other thing we did was we began to put the satellites into geosynchronous orbit so we didn’t need a tape. We just sent the information straight down to a ground station in the United States and that was that. So we lengthened the period before we would have to replace that satellite.”

13th ferret launch
The thirteenth heavy ferret satellite. The payload shroud is different from previous launches. (credit: Paul Gatherer)

Ferret subsatellites

The other major type of ferret satellite operated by the US Air Force during the 1960s was the ferret subsatellite type. The ferret subsatellites were deployed in large numbers in four basic categories and operated until the mid-1980s. Their mission, which was probably the monitoring of Soviet radar emitters, certainly overlapped somewhat with the Navy’s signals intelligence satellites. But it is now apparent that the Air Force ferret subsatellites flew in a large number of different configurations and their primary attribute may have been their ability to be adapted to a wide range of signals intelligence collection requirements.

The ferret subsatellites were deployed from several classes of photographic reconnaissance satellites. The subsatellites were attached to the aft rack of the Agena for early launches, alongside the engine, and used a solid rocket motor to boost them to higher orbit. Three test flights with science payloads were made before flights with sigint payloads began. How the satellites were attached to the massive KH-9 HEXAGON photo-reconnaissance satellite, which did not have an Agena-derived booster, remains unknown. In addition, the KH-7 GAMBIT’s Agena did not stay attached to the KH-7 itself, requiring that the subsatellite be deployed early in the mission, before the separation of the GAMBIT photo-reconnaissance satellite from the Agena.

On April 30, 1962, the primary contractor for the CORONA reconnaissance program, Lockheed Corporation, prepared briefing slides for a “Discoverer Research Program” to deploy small wheel-shaped spacecraft from the Agena aft rack during Discoverer launches. At that time Discoverer was the cover story for the CORONA reconnaissance program.

It is now apparent that the Air Force ferret subsatellites flew in a large number of different configurations and their primary attribute may have been their ability to be adapted to a wide range of signals intelligence collection requirements.

The Discoverer Research Program proposal was for a scientific satellite. The briefing charts indicated a seven-month development schedule from approval to launch. Considering that the first Agena subsatellite was ready for launch in March 1963, only eleven months later, it seems likely that the Discoverer Research Program of April 1962 was actually approved soon after Lockheed engineers made their proposal. Although this project may have been initially approved as a limited scientific effort, the Air Force may have quickly recognized the opportunity to launch small signals intelligence satellites piggyback on its other spacecraft launches, using the same payload bus as Lockheed proposed for the Discoverer Research Program.

Lockheed justified the satellite as a deployable payload from the Agena on three criteria. First, an alternative launch method would have utilized a Blue Scout launch vehicle at a cost of $855,000, whereas hitching a ride from a photo-reconnaissance flight was essentially free. Second, the orbital weight could be 225 pounds (102 kilograms) as opposed to 160 pounds (73 kilograms). And finally, the vehicle could have an active lifetime of two to six months versus only one month for the Blue Scout version. Equipment would have been located in two compartments around the perimeter of the circular spacecraft.

From the limited documentation available, Lockheed’s initial proposal was apparently simply for a satellite to take advantage of additional capability on its Agena upper stage, rather than to develop a cover story for a new signals intelligence satellite. But by the time the company proposed it, the Samos F-1 program had been canceled. Assuming that its mission was still valid, Lockheed’s proposal for a satellite deployed from existing missions must have been an attractive alternative.

The satellite that Lockheed actually built looks considerably different than Lockheed’s original wheel-shaped proposal. It was named Program 11, often abbreviated as P-11. The Program 11 satellite was a rectangular box and it seems likely that soon after they proposed the Discoverer Research Satellite, Lockheed engineers realized that they could make their satellite larger to take advantage of the rectangular space on the Agena aft rack, and yet still employ spin stabilization.

The satellites were attached to a mounting bracket on the aft rack of the Agena that swung outward 90 degrees, so that the satellite pointed in the direction of the Agena’s rocket bell. Because the CORONA satellites flew backwards in orbit, the mounting bracket actually caused the P-11 satellites to face toward the direction of flight so that when their rocket engines fired they gained velocity and thus entered a higher orbit.

The Program 11 designation was apparently applied to both the three scientific and several operational sigint satellites launched through 1965. At some point the designation Program 989 was applied to these satellites, although it is unknown when this started. As previously noted, at least one of these satellites was launched under the designation Program 770, although it is unclear if that designation was specifically applied to the subsatellite ferret.

In July 1964, the CIA investigated using the P-11 satellites in concert with the Mach 3 A-12 OXCART reconnaissance plane, which at the time was still referred to as the A-11. According to a declassified memo, an NRO official “sketched a plan whereby three P-11 satellites spaced 120 degrees apart in polar orbit would make north/south passes across the Soviet Union progressing say East to West but with 500 miles [800 kilometers] cross spacing between each trace at intervals of 30 minutes. The A-11 could fly diagonally across the Soviet Union stimulating the defense networks while the P-11s gathered the resulting elint data. He speculated the radars of interest may include Token, Tall King, Spoonrest.”

Such a mission would have been highly provocative, especially in light of American promises in the wake of the Gary Powers U-2 shootdown incident of May 1960 to not fly spyplanes over the Soviet Union. The mission, which was apparently only a theoretical proposal, never occurred.

A total of 44 subsatellites were launched as secondary payloads aboard LANYARD, ARGON, KH-7 GAMBIT, and KH-9 HEXAGON reconnaissance satellites between 1963 and 1985. One satellite was also deployed during a launch of several Navy small satellites aboard a Thorad Agena D in September 1969. In that case, the ferret subsatellite used its rocket motor to brake to an orbit lower than the other payloads rather than boost to a higher orbit. One satellite failed to reach orbit during the first launch in March 1963. Another satellite was probably carried aboard the last KH-9 HEXAGON launch, which exploded in April 1986.

During the latter 1980s Lockheed attempted to sell a commercial version of the subsatellite, which it had named the Small Research Satellite, or SRS, and released line drawings of the vehicle.

The first three P-11 satellites were dedicated science missions. The scientific results of the missions were published in the Journal of Geophysical Research. Two photographs of the first Lockheed subsatellite attached to the Agena aft rack of the first KH-6 LANYARD reconnaissance satellite have now been discovered. They depict the satellite in its closed, stowed configuration, revealing little about the design. This was a scientific mission prior to the advent of the sigint version. This launch was a failure and neither the LANYARD nor the subsatellite entered orbit.

However, during the latter 1980s Lockheed attempted to sell a commercial version of the subsatellite, which it had named the Small Research Satellite, or SRS, and released line drawings of the vehicle. The company indicated that the satellite had spin-stabilized and gravity-gradient stabilized versions.

Lockheed donated the prototype scientific subsatellite to the US Air Force Museum in Dayton, Ohio, where it resides today. The satellite on display features numerous small antennas. It hung for years with only a simple label. But in recent years the Air Force Museum created a webpage for the satellite. The webpage (not currently available) provides more information:

The Lockheed research satellite was designed to carry different types of scientific payloads to make it more versatile in investigating various characteristics of the space environment. Its maximum weight at launch was 350 lbs [159 kilograms] and it was programmed to spin in space from 60 to 80 revolutions per minute for stabilization purposes. The first launch of this type satellite was made in 1963 from an Agena space vehicle in orbit around the Earth. By firing one or more of its three solid propellant rocket engines, it could propel itself into an accurate, highly-elliptical polar orbit for the purpose of measuring radiation in the inner Van Allen belt. During hundreds of orbits and an active, useful life of more than 2 1/2 months, the Lockheed Research Satellite radioed back to Earth approximately 100 million measurements of scientific data. More than 20 versions of this satellite have been placed in Earth orbit.

Assuming that the three actual scientific satellites were all of the same type, then this means that at least 20 different versions of sigint ferret satellites were ultimately flown. There were four major categories.

The first category included the first three scientific satellites and four sigint satellites and probably constituted the Program 11 satellites. They all had orbits with perigees around 300 kilometers with inclinations from a low of 64.5 to a more usual 95.5 degrees based upon the initial inclination of their host launcher. They rode on CORONA, ARGON, LANYARD, and KH-7 GAMBIT launch vehicles and were used from 1963 until 1965.

The second category of satellites began flying in 1965, with 500-kilometer orbits and inclinations of 65.7 to 109.9 degrees. These orbits were generally similar to the Program 102 Agena ferret satellites. Twenty-six satellites of this type were launched. They deployed from KH-4A and KH-4B CORONA reconnaissance satellites and later from KH-9 HEXAGON reconnaissance satellites. A single satellite was also launched from a Long Tank Thrust Augmented Thor Agena D rocket carrying several Naval Research Lab payloads.

In 1976 a new category of satellites began flying with orbits of 600–700 kilometers and inclinations between 95.8 and 96.4 degrees. Five satellites of this type were launched, all aboard KH-9 HEXAGON reconnaissance satellites. The last was launched in June 1983, although it is probable that the last KH-9 HEXAGON, which exploded during launch, also carried one of these satellites.

The purpose of these satellites is unknown, but it seems likely that their mission was to try to intercept and characterize Soviet ground radar emissions. The Strategic Air Command had great interest in Soviet radar systems and needed accurate information in order to protect its strategic bombers. This requirement undoubtedly drove their deployment. New versions of the satellite may have been launched as the Soviet Union fielded new ground radars. The ferret subsatellite may have been a multi-purpose signals intelligence platform, a sigint truck capable of carrying equipment to intercept a variety of electronic emissions.

subsatellite and Agena
A small subsatellite mounted to the aft rack of the Agena upper stage.  Numerous small ferret satellites were launched in this manner. (credit: USAF)

Ferrets and the ABM problem

Whereas the GRAB and ferret subsatellite programs appear to have been largely driven by the requirements of the military services, another subsatellite program was the result of an interagency dispute.

Beginning in the early 1960s the US Intelligence Community became increasingly concerned with Soviet anti-ballistic missile (ABM) capabilities, particularly after the development of a new missile site near Tallinn, Estonia. The missiles at the site were clearly designed for high altitude operation, although just how high remained unknown. But Tallinn was not a high priority target worth defending, leading some in the Air Force to claim that this was a site for conducting “area defense” against American ICBMs. Equally confusing was the fact that no phased-array radars capable of directing ABMs were anywhere near the launch site.

CIA analysts argued that the Tallinn site was not an ABM site, whereas Air Force officials argued that it was, or at least could be, and pointed out that there were still many radars within the Soviet Union that the US had little information about. By summer 1966 this dispute resulted in a call for a revision of satellite signals intelligence collection efforts. By October, the Committee on Overhead Reconnaissance, known as COMOR, which selected targets to be viewed by American photo and sigint satellites, discussed a “consideration of requirement for collection against ABM/AES.” The abbreviation AES stood for anti-Earth satellite, or what we now refer to as ASAT. By November this subject was discussed again and had become an “urgent requirement for sigint satellite collection against Soviet ABM/AES systems.”

A few days later Director of Central Intelligence Richard Helms wrote a letter to the Deputy Secretary of Defense, Cyrus Vance, stating: “On November 17, the United States Intelligence Board (USIB) approved an urgent requirement for information on [Soviet anti-ballistic missile radar and “AES”] systems. It is essential that every effort be made to meet this requirement within the next twelve months. In evaluating the chance of early fulfillment of that requirement, I am convinced that, among the various sigint satellite systems presently available, the best hope lies in a concentrated [deleted] program. This program would involve qualitative improvement, as well as an expanded launch schedule, probably to as many as [deleted] per year. I believe that immediate steps should be taken to develop such a program and to make the necessary NRO funds available.”

By December a group of senior scientific intelligence advisors to the government met to discuss sigint issues in general. According to a letter by the two senior advisors, Edwin Land and Edward Purcell, “the Panel spent considerable time discussing systems which might meet the urgent requirement to determine the characteristics of the Soviet ABM systems. We believe that the Panel in general would agree that the decisions that would be influenced by the information gathered about these defenses are of such magnitude that we ought not be satisfied with any collection system [deleted more than 25 lines of text].”

CIA analysts argued that the Tallinn site was not an ABM site, whereas Air Force officials argued that it was, or at least could be, and pointed out that there were still many radars within the Soviet Union that the US had little information about.

Ultimately the National Reconnaissance Office decided that the best method of gathering this urgently needed information was to modify the existing ferret subsatellite design. In December 1968 a new class of subsatellite ferret began flying to focus on Soviet ABM radars. They had orbits of 1200–1400 kilometers at about 80.3 to 96.9 degrees inclination—significantly higher than their predecessors and requiring an additional kick motor to place them in the proper orbit. The higher orbit undoubtedly resulted from the need to keep the targets in view for a longer period of time. Satellites focused on SAM sites had many targets to locate and analyze, but the ABM ferrets had only a few. Seven satellites of this type were launched from KH-4A CORONA and KH-9 HEXAGON reconnaissance satellites between 1968 and 1983.

But although this had been an urgent requirement in late 1966, apparently requiring an increased launch rate, the urgency began to fade soon after the launch of the first satellite. By that time, Air Force officials had essentially conceded that Tallinn was not an ABM missile site (it was in fact intended to shoot down high-altitude, high-speed XB-70 Valkyrie bombers, which had been canceled before the site was even built). By the early 1970s, the United States and Soviet Union had also entered into a treaty to ban ABMs. This changed situation was reflected in the deployment of these satellites. Four were deployed between late 1968 and 1973, but only three more were deployed in the next ten years.


American signals intelligence satellites were of course only one aspect of a vast signals intelligence collection effort operated by the US Intelligence Community. The amount of information available on their early operation remains extremely limited, especially compared to other satellite intelligence collection operations. It may never be possible to write as detailed a history of signals intelligence satellites as it is for photo-reconnaissance satellites, but slowly we can assemble the edges of the puzzle and a few of its inner pieces.



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