Vintage Micro: The First ELINT Satellites

In today’s world, electronic intelligence or ELINT satellites are considered an important part of maintaining the nation’s security. While the National Reconnaissance Office (NRO) is tight lipped about its activities, it is generally known that the US maintains constellations of large and very capable satellites monitoring a whole range of transmissions from their perches in space. And despite this secrecy, today this capability is also at the heart of the debate about potential violations of the rights of citizens as well as causing problems with our allies.

In stark contrast with today, the original American ELINT satellites deployed over half a century ago were very modest in size and capabilities. Conceived and first launched before NRO was even founded, the existence of the first ELINT satellites was not even officially acknowledged until 1998 – years after the details of NRO’s once secret Corona reconnaissance satellite series started to be declassified. But despite being what would today be classified as “microsatellites”, the first ELINT satellites played an important role in the Cold War.

The Birth of ELINT Satellites

The idea to use satellites for ELINT dates back to studies performed before the dawn of the Space Age. America’s very first reconnaissance satellite program, known as WS-117L, included a signal intelligence capability when its requirements were secretly approved in March 1955 – almost six months before the announcement of the America’s first “official” satellite program, Vanguard. But as development of this program with its large and complicated satellites (which would include several early intelligence satellite series including Corona) plodded forward, a simpler solution was found to meet a more limited ELINT application.

Determining the location and operating characteristics of Soviet air defense radar installations was vitally important in developing electronic countermeasures and planning bomber missions into the Soviet Union in the event of war. In early 1958, an engineer at the Naval Research Laboratory (NRL) named Reid D. Mayo came up with an ingenious yet simple method to do just this while stranded in a snow storm during a family trip. Mayo’s idea was simply to have a small satellite relay in real time the S-band radar signals detected while overflying the Soviet Union directly to ground stations just over the border where they would be recorded. From the vantage point of its nominal 925-kilometer orbit, the satellite could detect radars within a 2,650 kilometer radius compared to just 320 kilometers typical for electronic “ferret” aircraft that regularly patrolled along Soviet borders. These recordings could then be analyzed on the ground to determine the position of Soviet radar installations and their signal characteristics.

The coverage over the Soviet Union and China expected from a single pass of a ELINT satellite in a 925-km orbit inclined 70 degrees to the equator. (NRL)

Back at NRL, Mayo’s concept was evaluated in more detail and it was found that the required ELINT payload could be easily accommodated inside a modified version of the “standard” 51-centimeter in diameter Vanguard satellite built at NRL thus greatly speeding its development (see “Vintage Micro: The Original Standardized Microsatellite”). In July of 1958, NRL proposed the concept under the codename Project Tattletale and received approval from President Eisenhower on August 24.

As with other forms of satellite surveillance at this time, Eisenhower was concerned about the perception of the US spying even on a secretive potential adversary like the Soviet Union. As a cover story and a means of making good use of available payload space inside the satellite, NRL scientists installed sensors originally developed as part of the Vanguard program’s science payload to monitor the Sun’s Lyman-α emissions in the ultraviolet as well as X-rays to perform some legitimate science. Publicly the satellite was called SOLRAD for “SOLar RADiation”. Its secret cover name was GRAB for “Galactic Radiation And Background”. But despite the security surrounding the project, an altered version of the name was leaked – GREB for “Galactic Radiation Experiment Background” or, according to some declassified documents, “Galactic Radiation Energy Balance”. After 1962, the secret name for this first series of ELINT satellites was Dyno. While the scientific mission of the satellite was well known, its ELINT mission was completely unknown to the public as well as to the scientists involved with the SOLRAD scientific instruments until it was declassified in 1998.

The SOLRAD/Dyno Satellite

Like the Vanguard satellite, Dyno consisted of a polished aluminum sphere with a diameter of 51 centimeters. Unlike the standard Vanguard satellite, the exterior sported six flat circular patches with a diameter of 23 centimeters each that carried 156 silicon solar cells to provide one watt of electrical power to recharge the payload’s batteries no matter the satellite’s orientation to the Sun. The SOLRAD scientific payload consisted of improved versions of the science hardware developed for the Vanguard program’s Package I and Ia. These instruments were a pair of detectors to measure solar Lyman-α emissions in the 105 to 135 nm range of the ultraviolet and second pair of detectors to measure solar X-rays in the 0.1 to 0.8 nm range (corresponding to photon energies in the 1.5 to 12 keV range). Despite multiple attempts, only the X-ray detector had been successfully orbited during the Vanguard program on Vanguard 3 launched in 1959 but radiation rendered the data unusable. Modifications to the instrument and SOLRAD’s lower 925-kilometer orbit would avoid this issue.

Unclassified diagram showing the major components of the SOLRAD 1 satellite. The “skin thermistors” in reality were the locations of the antennas used by the classified ELINT payload. Click on image to enlarge. (NRL)

For the secret ELINT mission, Dyno carried a single channel, fixed-frequency S-band crystal video receiver to detect Soviet radar transmissions. These signals were received using six monopole antennas (which were disguised as skin temperature sensors in public diagrams) for omnidirectional detection of signals. The received signals would then be transmitted in real time to the ground for 40 minutes upon command. Data were transmitted through a two-channel FM/AM 40 milliwatt transmitter via four whip antennas arranged around the circumference of the satellite. Peak power requirements for the on board equipment was six watts. The first Dyno satellites had a mass of just 19 kilograms making them “microsatellites” by today’s definition.

The first SOLRAD/Dyno satellite shown riding piggyback atop of Transit 2A in preparation for launch. (USN)

The Dyno satellites were launched as piggyback payloads with the US Navy’s experimental Transit navigation satellites using the Thor Able Star launch vehicle which was designed specifically to place payloads into medium-altitude orbits. Also known as the Thor Epsilon, this new launch vehicle was based on the earlier Thor Able which also spawned the long-lived Thor Delta or simply Delta family of rockets whose distant descendants still fly today. Like the three-stage Thor Able, the booster of the Thor Able Star was a modified USAF Thor IRBM built by Douglas Aircraft. The second stage of this two-stage rocket, built by Space Technology Laboratories, Inc., was 5.9 meters long and 1.4 meters in diameter giving it over twice the propellant load of the Thor Able second stage. Unlike its predecessors which relied on a separate third stage to orbit its payload, however, this second stage had an in-orbit restart capability. During a typical ascent, the Thor and the first burn of the second stage would place the stage and its payload into a short-lived, elliptical transfer orbit. After a 20-minute coast where the attitude was controlled by nitrogen gas jets, the stage’s AJ10-104 engine (which was similar in design to earlier engines used in the Thor Able and Vanguard second stages) would reignite near apogee to circularize the orbit. Once in its final orbit, Dyno would separate from the Transit satellite to begin its mission.

The First Dyno Launches

On June 22, 1960 at 1:54 AM EDT, Transit 2A and the first Dyno satellite, publically known as SOLRAD 1 and sometimes GREB 1, were successfully launched by Thor Able Star DM-21A No. 281 from Launch Complex 17B at Cape Canaveral and into orbit to become the first successful piggyback satellite launch. Because of some glitches in the operation of the Able Star second stage, a 611 by 1,046-kilometer orbit with an inclination of 66.7° was achieved instead of the desired 930-kilometer circular orbit. Despite the slightly elliptical orbit, Dyno 1 was ready to start its public scientific and secret ELINT missions.

The launch of Transit 2A and SOLRAD 1 atop of a Thor Able Star on June 22, 1960. (NRL)

Very quickly the SOLRAD payload, which made the claim of being the first astronomical satellite, returned useful data from its ultraviolet and X-ray detectors that had an immediate scientific impact. Analysis of the data showed that radio “fade outs” that affected long distance communications were caused by solar X-ray emissions that altered the radio-reflective properties of Earth’s ionosphere. But while the scientific data were quick in coming, the Eisenhower administration was wary of using the ELINT payload in the wake of the Gary Powers U-2 incident which had happened only two months earlier. The administration feared what the Soviet response might be if they detected the transmissions from Dyno 1 and required presidential authorization for every ELINT data collect.

The first test of the ELINT payload took place on July 5, 1960 as the satellite passed over Hawaii during orbit 199 well out of range of the Soviet Union. With this successful test, Dyno was deemed ready for its clandestine mission. Dyno 1 made a total of 22 authorized data collects over Soviet and Chinese territory before its ELINT payload unexpectedly stopped functioning after September 20. Despite the unexplained loss, the ELINT payload returned a huge amount of useful data. The surprisingly large number of signals detected not only demonstrated that the Soviet’s air defense radar system was much more extensive than originally thought, but it required the development of new analysis techniques to extract as much useful information as possible from the cacophony of signals in the recordings.  While the ELINT mission ended after only 90 days, SOLRAD’s scientific results continued to be transmitted to Earth until April 1961 when the satellite was finally commanded to turn off – another first for the US.

The next Dyno launch, in the guise of SOLRAD 2, took place on November 30, 1960 as a piggyback payload with Transit 3A. Thor Able Star DM-21A No. 283 lifted off from LC-17B but the Thor booster malfunctioned forcing range safety to detonate its destruct package. Unfortunately, debris from the wreck caused an international incident when it came down over Cuba allegedly killing a cow in the process. Future flights would be launched on a less southerly azimuth to avoid a repeat with the ascending rocket performing a “dog leg” maneuver to reach the required orbit inclination.

The Last Dyno Missions

The third Dyno satellite was part of a triple payload launch – the first one ever attempted. The primary payload on this launch was Transit 4A. The piggyback payloads were the next Dyno satellite named SOLRAD 3 (or sometimes called GREB 3) and another small satellite called Injun 1. This latter payload was a USAF-sponsored satellite with a mass of 18 kilograms (another microsatellite by today’s definition) carrying a set of radiation detectors built at the State University of Iowa for James Van Allen to study cosmic radiation and the Van Allen belts discovered three years earlier using the first Explorer satellites by Dr. Van Allen himself. The scientific payload of SOLRAD 3 was an X-ray detector similar to the one flown on the previous SOLRAD satellites. For this mission, the ELINT payload was upgraded so that two radar frequencies could be monitored instead of just a single frequency as on the earlier spacecraft. This newer satellite was the same size and configuration as before but the mass had increased to 25 kilograms.

Diagram showing the launch configuration for the first triple payload launch attempt with Transit 4A, Injun and SOLRAD/GREB 3 on top.

The triple payload lifted off atop Thor Able Star DM-21A No. 315 on June 29, 1961. While the payload achieved a 764 by 869-kilometer orbit with an inclination of 66.8°, the three satellites failed to separate from each other as planned. This was the second NRL piggyback payload that failed to separate once in orbit. The previous incident occurred with the launch of Transit 3B on February 21 which carried NRL’s LOFTI 1 (Low Frequency Transmission through the Ionosphere) which was also based on the SOLRAD design. After this latest glitch, NRL took direct responsibility for the separation mechanism and the problem never recurred.

Despite the separation problem, the mission was salvageable. To avoid electromagnetic interference between the piggyback payloads, the Injun and Dyno satellites simply operated on alternating days. By the time of this launch, the new Kennedy administration had come into office and removed restrictions on Dyno’s ELINT activities including the requirement to obtain White House approval for each data collect. Unencumbered by the old restrictions, much more frequent ELINT operations started on July 15, 1961 and continued for the next 14 months accumulating an immense volume of data on the Soviet air defense radar network. So much data was being collected that analysts simply could not keep up. Fortunately by October 1961, a new automated analysis system came on line to not only process the backlog of existing data but also handle data expected from the new Dyno satellites being prepared for launch as well as ELINT data from the USAF experimental Samos reconnaissance satellites.

A schematic showing the CONOPS (concept of operations) for the GRAB ELINT satellite. Click on image to enlarge. (NRO)

The fourth Dyno payload was launched as part of the Composite 1 mission which was the first attempt to launch five satellites on one rocket. SOLRAD 4 carried an expanded set of ultraviolet and X-ray detectors along with a secret two-channel ELINT package. In addition to SOLRAD 4, the Composite 1 flight included the 27-kilogram Injun 2, the 26-kilogram LOFTI 2 and the 16-kilogram SECOR (Sequential Collation of Range) designed to provide range calibration data for the USAF – all microsatellites by today’s definition. The fifth payload was the 4-kilogram SURCAL (Surveillance Calibration) which was to remain attached to the Able Star second stage and provide measurements for calibrating the Navy’s Space Surveillance System. Composite 1 lifted off from LC-17B atop Thor Able Star DM-21A No. 311 on January 23, 1962. Unfortunately a malfunction in the second stage prevented the innovative multi-satellite payload from reaching orbit.

The final Dyno launch was unique in the series in that it was launched as a solo payload on a Scout, all-solid rocket from Launch Complex D at Naval Missile Facility at Point Arguello, California (today known as SLC-5 in South Vandenberg AFB). Scout X-2 No. 11 lifted off on April 26, 1962 carrying SOLRAD 4B but a malfunction in the fourth stage prevented it from reaching orbit. With the last failure, the Dyno series of ELINT satellites was quietly retired with the last satellite unlaunched (which, in 2002, was donated to the National Air and Space Museum).

Closeup of the last unlaunched SOLRAD/Dyno satellite donated to the National Air and Space Museum in 2002. (NASM)

Although only two Dyno satellites were successfully placed into orbit and operated over a total of less than a year and a half, the huge volume of data gathered was enough for the American intelligence community to start to assess the true extent of the Soviet Union’s air defense system. A new and increasingly more sophisticated satellite series named Poppy would succeed Dyno to continue NRO’s secret ELINT activities until the end of that program in 1977 along with a host of other satellites which remain largely classified to this day. And the SOLRAD series would also continue as a separate NRL-sponsored scientific satellite program studying the Sun until SOLRAD 11B was finally shutdown in June 1979.

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Related Reading

“Vintage Micro: The Original Standardized Microsatellite”, Drew Ex Machina, July 5, 2014 [Post]

“The US Navy in the Space Age”, Space Views, June 26, 2000 [Article]

“Spy in the Sky”, Space Views, March 1, 1999 [Article]

General References

Philip J. Klass and Joseph C. Anselmo, “NRO Lifts Veil on First Sigint Mission”, Aviation Week & Space Technology, Vol. 148, No. 25, pp. 29, 32-33, June 22, 1998

Robert A. McDonald and Sharon K. Moreno, “Raising the Periscope… Grab and Poppy: America’s Early ELINT Satellites”, National Reconnaissance Office, Recognition Ceremony Edition, September 2005

Jonathan McDowell, “Naval Research Laboratory Satellites”, Journal of the British Interplanetary Society, Vol. 50, No. 11, pp. 427-432, November 1997

“Transit IV-A/INJUN/GREB III”, STL Space Log, Vol. 1, No. 7, pp. 44-45, December 1961

“Composite 1”, STL Space Log, Vol. 2, No. 2, pp. 23-24, June 1962

“History of the Poppy Satellite System”, National Reconnaissance Office document 56105-78 (declassified version), c1978

“U.S. Navy/NRO Program C Electronic Intelligence Satellites (1958-1977)”, National Reconnaissance Office document (declassified version), 3 September 1998