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DONKEY payload fairing
The July 1967 launch of the MULTIGROUP satellite that carried the DONKEY payload had a distinctive, unusual payload fairing.

That’ll do, DONKEY, that’ll do

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When the Manned Orbiting Laboratory (MOL) program started in late 1963, it was going to be an incredibly complex machine: both a human space station and a collection of military experiments and equipment for performing an operational intelligence collection mission. The centerpiece of MOL was going to be a large optics system for conducting photoreconnaissance, code-named DORIAN. But MOL would also operate other intelligence equipment, including a signals intelligence system. Over the next several years, as MOL moved from concepts and studies to becoming blueprints and designs, its managers began to realize how complicated it was and sought to simplify and streamline the spacecraft. In 1965, they decided to eliminate a communications intelligence collection payload called DONKEY. But although the mule might have taken a kick, it didn’t roll over. DONKEY still found a way to fly, the only MOL system that did.

Although the mule might have taken a kick, it didn’t roll over. DONKEY still found a way to fly, the only MOL system that did.

In summer 1964, Colonel John Copley, who had previously worked on the National Reconnaissance Office’s signals intelligence satellites at Los Angeles Air Force Base, was assigned to the MOL program at Air Force Headquarters. Copley was given the task of determining if there were signals intelligence applications for MOL, and in February 1965 he apparently focused on a specific mission. One idea—it is unclear if Copley came up with it or merely evaluated the proposal—was for a communications intelligence (“comint”) payload to intercept signals from a Soviet microwave communications system used by both civilian and military sectors. The precise target system remains classified, but it apparently consisted of a network of transmitters throughout the Soviet Union. Copley determined that intercepting the transmitters’ main beams would be difficult, but that collecting from their sidelobes, which radiated out from a transmitter from its sides like the feathers on a peacock, would increase intercept times while a satellite was overhead. In best case, it could gather enough information to determine what was being transmitted over the network, at least while the MOL was overhead.

Copley proposed that this signals intelligence collector should be included on MOL. It would use a six-foot (two-meter) diameter parabolic “wrapped rib” antenna that would unfold from the side of the big cylindrical MOL. Unlike an umbrella-type dish, the antenna wrapped flexible ribs and the mesh antenna strung between them around a central spoke, enabling a larger diameter antenna to be packed in a smaller volume. It is also possible that the plan was to also use the system to cue the MOL’s powerful DORIAN camera: the system would detect an emitter and point the camera towards it, although it is unclear how precisely the detector could locate a target, especially considering how small DORIAN’s field of view was.

E-Systems in Garland, Texas, and EDL-Sylvania developed a test system installed in the E-Systems facility. An Air Force helicopter flew a payload in an intercept pattern through the main beam and sidelobes of a microwave antenna at the E-Systems facility outside Dallas. EDL analysts examined the collected data and made recommendations for a mission. They determined that a three-axis stabilized satellite was needed for the payload. The payload activities were handled within the BYEMAN security control system under a unique management arrangement.

Sometime in 1965, with the MOL getting increasingly complicated, MOL program managers decided to eliminate the communications intelligence payload from the spacecraft. Although the details are somewhat murky, in November 1965, the SIGINT Working Group of the Committee on Overhead Requirements, which established requirements for US signals intelligence satellites, determined that the information transferred over the Soviet communications network had “high intelligence value.” The group declared that a system was required “to obtain sufficient technical data concerning the location, antenna patterns, and modulation of the [deleted] system to permit valid consideration of [a] follow-on collection system.” The group also indicated that this data could be useful for a planned geosynchronous signals intelligence collection system whose name was deleted from the document, but was almost certainly the CANYON satellite then being built by Lockheed and eventually launched in 1968.

DONKEY ran into problems almost immediately when its antenna pointing mechanism failed. This prevented it from performing the sidelobe collection mission.

With the payload no longer part of the MOL program, the National Reconnaissance Office officials soon transferred the project to the program office in Los Angeles that operated the NRO’s growing stable of signals intelligence satellites. It is unclear when or why the payload was named DONKEY, although it clearly had this codename by early 1966. Program managers and engineers began evaluating how to fly DONKEY. Apparently they initially considered putting the payload on a small dorm-refrigerator-sized P-11 satellite of the type routinely pushed off the back of Agena spacecraft with CORONA or GAMBIT photoreconnaissance payloads. But for unknown reasons the P-11 proved unsuitable.

Next, Copley and his colleagues evaluated the possibility of mounting the payload on the rear of an Agena-based signals intelligence spacecraft named MULTIGROUP. Starting in 1960, the Los Angeles program office had mounted a number of signals detection payloads on the aft rack of the Agena, so-called “AFTRACK” payloads. That program was discontinued by 1966, but DONKEY was designated as the last AFTRACK payload. The Agena was an all-around workhorse that served both as the second stage for Thor and Atlas rockets as well as a spacecraft in orbit providing power, stabilization and communications to various payloads.

The MULTIGROUP satellite would point nose down at the Earth, with its nest of antennas at the front and three solar panels sticking out at the back. But the aft rack of the MULTIGROUP Agena proved to be a poor location for the large antenna, because it would interfere with the solar panels that would be deployed in orbit. Engineers soon determined that the best location was the front of the MULTIGROUP satellite, which had gotten that name because of its ability to carry up to eight different payloads. Although the aft rack would not work, the front of the Agena presented problems as well because MULTIGROUP was crammed with payloads. The satellite already had three other outboard antennas, so packing an additional antenna into that space required careful planning—sort of like loading up a pack mule. Engineers came up with an unusual solution: a bulge in the side of the spacecraft’s payload fairing to fit the extra antenna for DONKEY.

On July 24, 1967, the second MULTIGROUP satellite was launched carrying the DONKEY payload. After the Agena placed it in orbit and the payload fairing was jettisoned, the Agena pitched nose down and MULTIGROUP began deploying its antennas. Officially, the mission consisted of several MULTIGROUP payloads looking at a range of frequency bands, DONKEY, and another payload codenamed SETTER, named after a pointing dog because of its ability to accurately locate the emitters that it detected.

Although nobody knew it at the time, DONKEY turned out to be the only operational intelligence legacy of the Manned Orbiting Laboratory program.

DONKEY ran into problems almost immediately when its antenna pointing mechanism failed. This prevented it from performing the sidelobe collection mission. It could not gather signals for long enough to provide useful intelligence about them. It is unclear if SETTER provided location data for the things that DONKEY detected, but DONKEY was still able to map emitter locations in the Soviet Union, leading to development of a grid that indicated a large majority of the emitters throughout the Soviet landmass. That data proved valuable for later collection activities that remain classified.

DONKEY also made it possible to map communications facilities located at Sary Shagan, the sprawling Soviet radar and anti-ballistic missile testing facility on the edge of Lake Balkhash in Kazakhstan. Sary Shagan’s radars tracked ballistic missiles as well as satellites, but they also had to communicate with other facilities and Moscow, and DONKEY helped figure out how the place was connected.

DONKEY had an independent downlink and operated for 182 days, 30 days longer than the other MULTIGROUP payloads due to a failure of their data link transmitter. Although nobody knew it at the time, DONKEY turned out to be the only operational intelligence legacy of the Manned Orbiting Laboratory program. MOL was canceled two years after DONKEY flew, and none of its hardware made it into space. The little payload was the only MOL payload that sprouted wings and took flight.