SOLRAD (short for "SOLar RADiation," sometimes presented as "SOLRAD") was an American series of satellites sponsored by the US Navy in a program to continuously monitor the Sun. SOLRAD was the Naval Research Laboratory's first post-Vanguard satellite. [1]
Until the Kennedy administration, American satellite launches were unclassified. [2] As a result, the United States Air Force and the Navy found themselves in the awkward position of wanting to orbit spy satellites but not reveal their nature to potential enemies. Just as the Air Force elected to pair their capsule film recovery satellites with biological payloads under the Discoverer program, so did the Navy develop a scientific cover for its GRAB series of radio/radar surveillance (ELINT) satellites.
The field of solar X-ray astronomy lent itself well to such an application. As the Earth's atmosphere absorbs extraterrestrial X-ray sources (of which the Sun is by far the most prominent), it is necessary to send sensors high in or above the atmosphere to detect them. Otherwise, a vast spectrum of solar output is unavailable to Earthbound scientists. [3]
Thus, the GRAB satellites would be equipped with X-ray sensors such that they could conduct publicly available scientific research while secretly spying on other countries' military installations. Moreover, through continuous observation of the Sun, the SOLRAD satellites would help the military better understand the effect of solar activity (including solar flares) on radio communications. [4]
When the National Aeronautics and Space Administration was established on July 29, 1958, most of the NRL Vanguard group's 200 scientists and engineers became the core of NASA's spaceflight activities (though the group remained housed at NRL until the new facilities at the Goddard Space Flight Center in Beltsville, Md. became available in September 1960).
Despite this exodus, NRL satellite and space-based research continued. Through the advocacy of NRL engineer Martin Votaw, a small contingent of remaining NRL rocket scientists and technicians regrouped to form the Satellite Techniques Branch headed by Votaw.
Their first project was SOLRAD. The new branch was tasked with creating the engineering hardware of the "satellite bus," responsible for the structure, power supply, command, telemetry and the coordination of a satellite, along with its interface with the booster. The branch also handled any special circuitry needed to support the satellite payload. [5]
The SOLRADs were not a standardized series of satellites. The first five SOLRADs, launched 1960–1962, were scientific payloads aboard GRAB ELINT satellites, whose primary mission was to monitor foreign radar and communications systems. Starting in 1963, the next three SOLRADs were stand-alone satellites co-launched with next-generation POPPY surveillance satellites, [6] and beginning with SOLRAD 8, in 1965, SOLRADs were launched alone under the auspices of the Explorer program. [7]
| Name | Launch date | International Designators | Other names | Launch vehicle |
|---|---|---|---|---|
| SOLRAD mass simulator | 13 April 1960 | 1960-003C | – | Thor DM-21 Ablestar [8] |
| SOLRAD 1 | 22 June 1960 | 1960-007B | GRAB-1 | Thor DM-21 Ablestar |
| SOLRAD 2 | 30 November 1960 (failed launch) | SRD-2 | GRAB-2 | Thor DM-21 Ablestar |
| SOLRAD 3 | 29 June 1961 | 1961-015B | GRAB-3a, Injun 1 | Thor DM-21 Ablestar |
| SOLRAD 4 | 24 January 1962 (failed launch) | GRAB, Injun 2 [9] | Thor DM-21 Ablestar [7] | |
| SOLRAD 4B | 26 April 1962 (failed launch) | SRAD4B | GRAB-3b | Scout X-2 |
| SOLRAD 5 | Not launched | – | GRAB | – |
| SOLRAD 6 | 15 June 1963 | 1963-021C | Solrad 6A [10] | Thor-Agena D |
| SOLRAD 7A | 11 January 1964 | 1964-001D | Solrad 6 [11] | Thor Augmented Delta-Agena D |
| SOLRAD 7B | 9 March 1965 | 1965-016D | – | Thor Augmented Delta-Agena D |
| SOLRAD 8 | 19 November 1965 | 1965-093A | Explorer 30 | Scout X-4 |
| SOLRAD 9 | 5 March 1968 | 1968-017A | Explorer 37 | Scout B-1 S160C |
| SOLRAD 10 | 9 July 1971 | 1971-058A | Explorer 44 | Scout B S177C |
| SOLRAD 11A | 14 March 1976 | 1976-023C | Titan IIIC | |
| SOLRAD 11B | 14 March 1976 | 1976-023D | Titan IIIC | |
| SOLRAD 11C | Not launched | SRD-11C | – |
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Vanguard 3 is a scientific satellite that was launched into Earth orbit by the Vanguard SLV-7 on 18 September 1959, the third successful Vanguard launch out of eleven attempts. Vanguard rocket: Vanguard Satellite Launch Vehicle-7 (SLV-7) was an unused Vanguard TV-4BU rocket, updated to the final production Satellite Launch Vehicle (SLV).
Galactic Radiation and Background (GRAB) was the first successful United States orbital surveillance program, comprising a series of five Naval Research Laboratory electronic surveillance and solar astronomy satellites, launched from 1960 to 1962. Though only two of the five satellites made it into orbit, they returned a wealth of information on Soviet air defense radar capabilities as well as useful astronomical observations of the Sun.
Thor was a US space launch vehicle derived from the PGM-17 Thor intermediate-range ballistic missile. The Thor rocket was the first member of the Delta rocket family of space launch vehicles. The last launch of a direct derivative of the Thor missile occurred in 2018 as the first stage of the final Delta II.
SOLRAD 4B was a solar X-ray, ultraviolet, and electronic surveillance satellite. Developed by the United States Navy's United States Naval Research Laboratory, it was the fifth in both the SOLRAD and the GRAB programs.
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Vanguard TV-5, also called Vanguard Test Vehicle-Five, was a failed flight of the American Vanguard rocket following the successful launch of Vanguard 1 on Vanguard TV-4. Vanguard TV-5 launched on 29 April 1958 at 02:53:00 GMT, from Launch Complex 18A at the Cape Canaveral Air Force Station. The rocket was unsuccessful in its attempt to place an unnamed satellite into orbit.
Solrad 9, also known Explorer 37 and Explorer SE-B, was one of the SOLRAD program that began in 1960 to provide continuous coverage of solar radiation with a set of standard photometers.
Solrad 10, also known Explorer 44, NRL-PL 165 and Explorer SE-C, was one of the SOLRAD series designed to provide continuous coverage of wavelength and intensity changes in solar radiation in the UV, soft and hard X-ray regions. The satellite also mapped the celestial sphere using a high-sensitivity X-ray detector.
Explorer 44,, was a NASA satellite was one of the SOLRAD program that began in 1960 to provide continuous coverage of solar radiation with a set of standard photometers. Explorer 44 was a spin-stabilized satellite, was the third in a series of SOLar RADiation spacecraft (SOLRAD) designed to provide continuous coverage of wavelength and intensity changes in solar radiation in the UV, soft, and hard X-ray regions. It also mapped the celestial sphere using a high-sensitivity X-ray detector. Information collected was expected to contribute to a better understanding of the physical processes involved in solar flares and other solar activity, and the potential effects of this activity on short-wave communications, as well as on future human space travel. For the period of July 1971 to June 1973, the core memory data of Explorer 44 were used rather than those from Explorer 37. The Explorer 44 core memory failed on 11 June 1973, and Explorer 37 was heavily used until 25 February 1974, when the gas supply of the attitude control system was exhausted.
SOLRAD 7A was the seventh solar X-Ray monitoring satellite in the SOLRAD series, and the fourth to successfully orbit the Earth. It was boosted into orbit along with four other military satellites atop a Thor Augmented Delta-Agena D rocket on January 11, 1964. Data returned by SOLRAD 7A dramatically revised scientific models of the solar corona.
SOLRAD1 is the public designation for SOLRAD/GRAB 1, a combination science and surveillance satellite launched into orbit on 22 June 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.
SOLRAD 2 was the public designation for a combination surveillance and solar X-rays and ultraviolet scientific satellite, the second in the SOLRAD program developed by the United States Navy's Naval Research Laboratory. The SOLRAD scientific package aboard the satellite provided cover for the GRAB electronic surveillance package, the mission of which was to map the Soviet Union's air defense radar network.
SOLRAD 3 was a solar X-ray satellite, the third in the SOLRAD program. Developed by the United States Navy's Naval Research Laboratory (USNRL), it shared satellite space with and provided cover for the Navy's GRAB 2, a secret electronic surveillance program.
SOLRAD 6 was the sixth solar X-ray monitoring satellite in the United States Navy's SOLRAD series, the third in the series to successfully orbit. It was launched along with POPPY 2, an ELINT surveillance package, as well as three other satellites, boosted into orbit via a Thor Augmented Delta-Agena D rocket on June 15, 1963.
SOLRAD 4 was a solar X-rays, ultraviolet, and electronic surveillance satellite. Developed by the United States Navy's United States Naval Research Laboratory (USNRL), it was the fourth in both the SOLRAD and the GRAB programs.
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SOLRAD 7B was the eighth solar X-Ray monitoring satellite in the SOLRAD series and the fifth to successfully orbit the Earth. It was launched via Thor Augmented Delta-Agena D along with seven other satellites on March 9, 1965. The satellite provided continuous coverage of the Sun during the International Quiet Solar Year from March through October 1965.