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SOLRAD (SOLar RADiation) 1 is the public designation for SOLRAD/GRAB 1, a combination science and surveillance satellite launched into orbit on June 22, 1960. It was the first satellite to successfully observe solar X-rays, the first to conduct surveillance from orbit, and the first to be launched with another instrumented satellite (the unrelated navigation satellite, Transit 2A).

Galactic Radiation and Background satellite 1.jpg
SOLRAD/GRAB 1 model at the National Cryptologic Museum
Mission typeSolar X-Ray
COSPAR ID1960-007B
SATCAT no.1960-007B
Spacecraft properties
Launch mass19.05 kilograms (42 lb)
Start of mission
Launch dateJune 22, 1960 05:54 (1960-06-22UTC05:54Z) UTC
RocketThor DM-21 Ablestar
Launch siteCape Canaveral LC17B
End of mission
DeactivatedApril 1961
Orbital parameters
Reference systemGeocentric
RegimeLow Earth
Perigee altitude614 kilometers (382 mi)
Apogee altitude1,061 kilometers (659 mi)[1]
Period101.70 minutes

Developed by the United States Navy's Naval Research Laboratory (NRL), the satellite was in many ways a direct successor to NRL's Project Vanguard, the first American satellite program. The satellite's scientific mission was a success, sending useful data until November 1960 that determined normal solar X-ray output and confirmed the connection between increased solar X-ray activity and radio fade-outs.

The SOLRAD scientific package aboard the satellite provided cover for the Galactic Radiation and Background (GRAB) electronic surveillance package, whose mission was to map the Soviet Union's air defense radar network. The GRAB mission was also successful, operating until September 22, 1960, and revealing that the Soviet air defense radar network was more extensive than had been expected. SOLRAD/GRAB 1 was switched off in April 1961, making it the first satellite to be remotely deactivated.



SOLRAD 1 on top of Transit 2A with four of its creators.[2] From left: Martin J. Votaw, George G. Kronmiller, Alfred R. Conover, and Roy A. Harding.

In 1957 the Soviet Union began deploying the S-75 Dvina surface-to-air missile, controlled by Fan Song fire control radars. This development made penetration of Soviet air space by American bombers more dangerous. The United States Air Force began a program of cataloging the rough location and individual operating frequencies of these radars, using electronic reconnaissance aircraft flying off the borders of the Soviet Union. This program provided information on radars on the periphery of the Soviet Union, but information on the sites in the interior of the country was lacking. Some experiments were carried out using radio telescopes looking for serendipitous Soviet radar reflections off the Moon, but this proved an inadequate solution to the problem.[3]:362

In March 1958,[4]:4 while the United States Naval Research Laboratory (NRL) was heavily involved in Project Vanguard, the United States Navy's effort to launch a satellite, NRL engineer Reid D. Mayo determined that a Vanguard derivative could be used to map Soviet missile sites. Mayo had previously developed a system for submarines whereby they could evade anti-submarine aircraft by picking up their radar signals. Physically small and mechanically robust, it could be adapted to fit inside the small Vanguard frame.[3]:364

Mayo presented the idea to Howard Lorenzen, head of the NRL's countermeasures branch. Lorenzen promoted the idea within the Department of Defense, and six months later the concept was approved under the name "Tattletale".[3]:364 President Eisenhower approved full development of the program on August 24, 1959.[4]:4

After a news leak by The New York Times, Eisenhower cancelled the project. The project was restarted under the name "Walnut" (the satellite component given the name "DYNO"[2]:140, 151) after heightened security had been implemented, including greater oversight and restriction of access to "need-to-know" personnel.[5]:2 American space launches were not classified at the time,[6][7] and a co-flying cover mission that would share space with DYNO was desired to conceal DYNO's electronic surveillance mission from its intended targets.[8]:300

The study of the Sun's electromagnetic spectrum provided an ideal cover opportunity. The Navy had wanted to determine the role of solar flares in radio communications disruptions[8]:300 and the level of hazard to satellites and astronauts posed by ultraviolet and X-ray radiation.[9]:76 Such a study had not previously been possible, as the Earth's atmosphere blocks the Sun's X-ray and ultraviolet output from ground observation. Moreover, solar output is unpredictable and fluctuates rapidly, making sub-orbital sounding rockets inadequate for the observation task. A satellite was required for long-term, continuous study of the complete solar spectrum.[10]:5–6, 63–65[11]

Wavelengths of light blocked by Earth's atmosphere

The NRL already had a purpose-built solar observatory in the form of Vanguard 3, which had been launched in 1959. Vanguard 3 had carried X-ray and ultraviolet detectors, though they had been completely saturated by the background radiation of the Van Allen radiation belt.[10]:63 Development of the DYNO satellite from the Vanguard design was managed by NRL engineer Martin Votaw, leading a team of Project Vanguard engineers and scientists who had not migrated to NASA.[12] The dual-purpose satellite was renamed GRAB ("Galactic Radiation And Background"), sometimes called GREB ("Galactic Radiation Experiment Background"), and referred to in its scientific capacity as SOLRAD ("SOLar RADiation").[2]:142, 149[8]:300

A dummy mass simulator SOLRAD was successfully launched on April 13, 1960, attached to Transit 1B,[8]:301 proving the dual satellite launch technique.[13] On May 5, 1960, just four days after the downing of Gary Powers' U-2 flight over the Soviet Union highlighted the vulnerability of aircraft-based surveillance, President Eisenhower approved the launch of an operational SOLRAD satellite.[14]:32


SOLRAD 1 schematic

Like Vanguard 3, SOLRAD/GRAB 1 was roughly spherical, 51 centimeters (20 in) in diameter, and powered by six circular patches of solar cells.[5]:10 SOLRAD/GRAB 1 was slightly lighter, massing 19.05 kilograms (42 lb)[5]:A1-2 (as opposed to Vanguard's 23.7 kilograms (52 lb)).[15] The solar cells powered nine D cell batteries in series (12 volts total)[5]:10 providing 6 watts of power.[14]:32

The satellite's SOLRAD scientific package included two Lyman-alpha photometers (nitric oxide ion chambers) for the study of ultraviolet light in the 1050-1050 Å wavelength range and one X-ray photometer (an argon ion chamber) in the 2–8 Å wavelength range, all mounted around the equator of the satellite.[16]

The satellite's GRAB surveillance equipment was designed to detect Soviet air defense radars broadcasting on the S band (1,550–3,900 MHz).[14]:29, 32 over a circular area 6,500 kilometers (4,000 mi) in diameter beneath it.[2]:108 A receiver in the satellite was tuned to the approximate frequency of the radars, and its output was used to trigger a separate VHF transmitter in the spacecraft. As it traveled over the Soviet Union, the satellite would detect the pulses from the missile radars and immediately re-broadcast them to American ground stations within range, which would record the signals and send them to the NRL for analysis. Although GRAB's receiver was omnidirectional, by looking for the same signals on multiple passes and comparing that to the known location of the satellite, the rough location of the radars could be determined, along with their exact pulse repetition frequency.[4]:4–7[2]:108

"NSA Data Reduction", indicating the intelligence to be derived by processing the satellite downlink

Telemetry was sent via four whip-style 63.5 centimeters (25.0 in) long antennas mounted on SOLRAD's equator.[9]:76 Scientific telemetry was sent on 108 MHz,[9]:78 the International Geophysical Year standard frequency used by Vanguard.[17]:84, 185 Commands from the ground and electronic surveillance were collected via smaller antennas on 139 MHz.[4]:7 Data received on the ground was recorded on magnetic tape and couriered back to the NRL, where it was evaluated, duplicated, and forwarded to the National Security Agency (NSA) at Fort Meade, Maryland, and the Strategic Air Command at Offut Air Force Base Omaha, Nebraska, for further analysis and processing.[18]

Like most early automatic spacecraft, SOLRAD/GRAB 1, though spin stabilized,[8]:300 lacked attitude control systems and thus scanned the whole sky without focusing on a particular source.[10]:13 So that scientists could properly interpret the source of the X-rays detected by SOLRAD/GRAB 1, the spacecraft carried a vacuum photocell to determine when the Sun was striking its photometers and the angle at which sunlight hit them.[10]:64

Launch and orbitingEdit

Lift-off of the Thor Able Star rocket with Transit 2A and SOLRAD 1 satellites

SOLRAD/GRAB 1 was launched at 05:54 UTC on June 22, 1960, via Thor DM-21 Ablestar launch system from Cape Canaveral LC17B.[13][19] The launch marked the first time two instrumented satellites had been carried to orbit on the same booster. SOLRAD/GRAB 1 initially circled the Earth once every 101½ minutes,[20] varying from 611 kilometers (380 mi) to 1,046 kilometers (650 mi) in altitude; this was a deviation from the planned 930 kilometers (580 mi) circular orbit, caused by glitches in the second stage of the booster,[21] but it did not affect the satellite's objectives.[19]

Scientific resultsEdit

SOLRAD/GRAB 1, the world's first orbital solar observatory, transmitted more than 500 batches of scientific data between June and November 1960,[10]:64–65 after which it became impossible to determine the angle at which the Sun hit the SOLRAD experiments.[22] Nevertheless, SOLRAD/GRAB 1 continued to send data until April 1961, when the spacecraft was switched off from the ground. This marked the first time a satellite had been remotely deactivated.[21]

The satellite communicated results in real-time, which meant that data could only be received when there was a tracking station within range – either one of Vanguard's Minitrack stations or a few other isolated receivers.[10]:64 Thus, just one to ten minutes per orbit,[22] some 1.2% of the satellite's active time, returned solar observations. The magnetic deflectors proved effective, allowing SOLRAD/GRAB 1 to become the first satellite to successfully observe solar X-rays.[10] However, they also interacted with the Earth's magnetic field, causing the satellite to precess (wobble around its axis like a spinning top) so that its sensors were in shadow half of the time the satellite was in sunlight.[10]:64


Approximately 20% of SOLRAD's data transmissions contained X-ray measurements, sufficient to establish the Sun's normal X-ray radiation levels (in the 2–8 Å range of detection) during times of inactivity: less than 6x10−11 Joules/cm2/sec. When X-ray output was observed strongly in excess of this baseline, it was usually correlated with solar activity visible from the ground. The data also showed that the X-ray output could change significantly in as little as one minute, underscoring the need for constant observation.[10]:64–65

When detectable X-ray output exceeded three times the normal rate,[10]:64–65 radio fade-outs occurred, confirming the link between solar X-ray variability and the strength of the Earth's ionized thermospheric layers.[12] These fade-outs were found to not just be caused by solar flares, but also by active solar prominence regions, bright surges, and subflares at the edge (or limb) of the Sun.[10]:64–65


SOLRAD/GRAB 1 did not find a correlation between solar ultraviolet output and thermospheric disturbance,[10]:53 and the Lyman-Alpha detectors were excluded from the later SOLRAD 3/GRAB 2 mission.[23]:28

Nuclear test monitoringEdit

It had been hoped during design and development that SOLRAD/GRAB 1 would be able to identify above-ground atomic tests, which produced strong emissions of X-rays in the bands that the satellite could detect. If a nuclear test ban treaty between the United States and the Soviet Union were to go into effect, SOLRAD/GRAB 1 or its successors might then be able to detect unauthorized tests by the Soviets. However, no spikes corresponding to known Soviet atomic tests were conclusively found in SOLRAD/GRAB 1's data. The Vela-Hotel satellites were later purpose-built for the task after the ratification of the Partial Nuclear Test Ban Treaty in 1963.[24]

GRAB radio control hut and team overseas

GRAB resultsEdit

SOLRAD/GRAB 1 was the world's first operational surveillance satellite. For fear that the Soviets would discover the satellite's espionage mission, and mindful of the problems caused by the U-2 incident,[25] President Eisenhower insisted that every GRAB transmission be personally approved by him,[14]:32 and that transmissions not be made on successive passes.[25] Thus, though the satellite's surveillance equipment functioned for the 92 days from launch until their failure on September 22, 1960, GRAB 1 only returned 22 batches of data, its first delivered on July 5, 1960[21] to the station at Wahiawa, Hawaii, well out of the range of Soviet detection.[5]:3 Even this first limited surveillance endeavor saturated the ground teams' ability to analyze and process the data[5]:39 and yielded valuable information, including the revelation that Soviet air defense activity was more extensive than expected.[21]

Legacy and statusEdit

The SOLRAD/GRAB series flew four more times finishing with the SOLRAD 4B mission launched April 26, 1962. Of the five SOLRAD/GRAB missions, only SOLRAD/GRAB 1 and SOLRAD 3/GRAB 2 were successes, the others failing to reach orbit. SOLRADs 6, 7A, and 7B co-flew with GRAB's signals intelligence successor, Poppy, 1963–1965. The final five SOLRAD satellites (8, 9, 10, 11A, and 11B) were stand-alone scientific satellites, three of which were also given NASA Explorer program numbers. These flew from 1965–1976. In all, there were thirteen operational satellites given the SOLRAD designation.[8]:301–302 The GRAB program was declassified in 1998.[21]

As of June 2019, SOLRAD/GRAB 1 (COSPAR ID 1960-007B)[16] is still in orbit.[26] The backup for the SOLRAD/GRAB 1 mission is on display at the Smithsonian National Air and Space Museum.[27]

See alsoEdit


  1. ^ "SOLRAD 1, Trajectory Details". NASA Space Science Data Coordinated Archive. Retrieved April 14, 2019.
  2. ^ a b c d e "Review and Redaction Guide" (PDF). National Reconnaissance Office. 2008. Retrieved January 24, 2019.
  3. ^ a b c Bamford, James (December 18, 2007). Body of Secrets: Anatomy of the Ultra-Secret National Security Agency. Knopf Doubleday Publishing Group. ISBN 978-0-307-42505-8.
  4. ^ a b c d McDonald, Robert A.; Moreno, Sharon K. "GRAB and POPPY: America's Early ELINT Satellites" (PDF). National Reconnaissance Office. Retrieved February 11, 2019.
  5. ^ a b c d e f "History of the Poppy Satellite System" (PDF). National Reconnaissance Office. August 14, 2006. Retrieved February 28, 2010.
  6. ^ Day, Dwayne A.; Logsdon, John M.; Latell, Brian (1998). Eye in the Sky: The Story of the Corona Spy Satellites. Washington and London: Smithsonian Institution Press. p. 176. ISBN 978-1-56098-830-4.
  7. ^ "Space Science and Exploration". Collier's Encyclopedia. New York: Crowell-Collier Publishing Company. 1964. p. 356. OCLC 1032873498.
  8. ^ a b c d e f American Astronautical Society (August 23, 2010). Space Exploration and Humanity: A Historical Encyclopedia [2 volumes]: A Historical Encyclopedia. Santa Barbara, Calif: ABC-CLIO. ISBN 978-1-85109-519-3.
  9. ^ a b c "'Bonus' Payload Set for Transit 2A Orbit". Aviation Week and Space Technology. New York: McGraw Hill Publishing Company. June 20, 1960. Archived from the original on January 9, 2019. Retrieved January 8, 2019.
  10. ^ a b c d e f g h i j k l Significant Achievements in Solar Physics 1958–1964. Washington D.C.: NASA. 1966. OCLC 860060668.
  11. ^ Committee on the Navy's Needs in Space for Providing Future Capabilities, Naval Studies Board, Division on Engineering and Physical Sciences, National Research Council of the National Academies (2005). "Appendix A: Department of the Navy History in Space". Navy's Needs in Space for Providing Future Capabilities. Washington D.C.: The National Academies Press. p. 157. doi:10.17226/11299. ISBN 978-0-309-18120-4. Archived from the original on January 7, 2019. Retrieved January 6, 2019.
  12. ^ a b Parry, Daniel (October 2, 2011). "NRL Center for Space Technology Reaches Century Mark in Orbiting Spacecraft Launches". U.S. Naval Research Laboratory. Archived from the original on January 7, 2019. Retrieved January 12, 2019.
  13. ^ a b McDowell, Jonathan. "Launch Log". Jonathon's Space Report. Retrieved December 30, 2018.
  14. ^ a b c d "NRO Lifts Veil On First Sigint Mission". Aviation Week and Space Technology. New York: McGraw Hill Publishing Company. June 22, 1998. Retrieved March 6, 2019.
  15. ^ "Vanguard 3". NASA Space Science Data Coordinated Archive. Retrieved January 25, 2019.
  16. ^ a b "SOLRAD 1". NASA Space Science Data Coordinated Archive. Retrieved April 4, 2019.
  17. ^ Constance Green and Milton Lomask (1970). Vanguard — a History. Washington D.C.: National Aeronautics and Space Administration. ISBN 978-1-97353-209-5. SP-4202.
  18. ^ "G R A B, Galactic RAdiation and Background,World's First Reconnaissance Satellite". U.S. Naval Research Laboratory. Archived from the original on July 26, 2007. Retrieved April 14, 2019.
  19. ^ a b "Busy Day at the Cape! Four Shots Successful". Chicago Daily Tribune. Associated Press. June 23, 1960. p. 6 – via
  20. ^ Benedict, Howard (June 22, 1960). "Single Rocket Puts Two Satellites in Orbit". Alabama Journal. Montgomery, Alabama. Associated Press. p. 6 – via
  21. ^ a b c d e LePage, Andrew. "Vintage Micro: The First ELINT Satellites". Drew Ex Machina. Retrieved January 18, 2019.
  22. ^ a b Kahler, S. W.; Kreplin, R. W. (1991). "The NRL Solrad X-ray Detectors: a Summary of the Observations and a Comparison with the SMS/GOES Detectors". Solar Physics. 133 (2): 378. Bibcode:1991SoPh..133..371K. doi:10.1007/BF00149895.
  23. ^ "Transit, Two Small Satellites Work Despite Malfunction". Aviation Week and Space Technology. New York: McGraw Hill Publishing Company. July 10, 1961. Archived from the original on January 10, 2019. Retrieved January 8, 2019.
  24. ^ Dr. Herbert Friedman (1987). Origins of High-altitude Research in the Navy. Washington, D.C.: National Academies. p. 32. OCLC 19708021. NAP:16277.
  25. ^ a b "The Navy's Spy Missions in Space". U.S. Naval Research Laboratory. Retrieved April 21, 2019.
  26. ^ "SOLRAD 1 (GREB)". Archived from the original on January 6, 2019. Retrieved January 8, 2019.
  27. ^ "Satellite, Electronic Intelligence, Galactic Radiation And Background, (GRAB-1)". Smithsonian. Retrieved April 25, 2019.

External linksEdit