SOLRAD (SOLar RADiation) 1 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 (the unrelated navigation satellite, Transit 2A).
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 22 September 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.
Background
SOLRAD 1 on top of Transit 2A with four of its creators. 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 Dvinasurface-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]:364President Eisenhower approved full development of the program on 24 August 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-rayradiation.[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 13 April 1960, attached to Transit 1B,[8]:301 proving the dual satellite launch technique.[13] On 5 May 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
Spacecraft
SOLRAD 1 schematic
Like Vanguard 3, SOLRAD/GRAB 1 was roughly spherical, 51cm (20in) in diameter, and powered by six circular patches of solar cells.[5]:10 SOLRAD/GRAB 1 was slightly lighter, massing 19.05kg (42.0lb)[5]:A1-2 (as opposed to Vanguard's 23.7kg (52lb)).[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-alphaphotometers (nitric oxide ion chambers) for the study of ultraviolet light in the 1050–1350Å wavelength range and one X-ray photometer (an argon ion chamber) in the 2–8Å 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 (1550–3900 MHz).[14]:29,32 over a circular area 6,500km (4,000mi) 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 Very high frequency (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-style63.5cm (25.0in) long antennas mounted on SOLRAD's equator.[9]:76 Scientific telemetry was sent on 108MHz,[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 139MHz.[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 BaseOmaha, 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 orbiting
Lift-off of the Thor-Ablestar rocket with Transit 2A and SOLRAD 1 satellites.
SOLRAD/GRAB 1 was launched at 05:54 GMT on 22 June 1960, via Thor-Ablestarlaunch system from Cape Canaveral LC-17B.[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 101.7 minutes,[20] varying from 614km (382mi) to 1,046km (650mi) in altitude; this was a deviation from the planned 930km (580mi) circular orbit, caused by glitches in the second stage of the booster,[21] but it did not affect the satellite's objectives.[19]
Scientific results
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
X-rays
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
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 results
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 22 September 1960, GRAB 1 only returned 22 batches of data, its first delivered on 5 July 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 status
The SOLRAD/GRAB series flew four more times finishing with the SOLRAD 4B mission launched on 26 April 1962. Of the five SOLRAD/GRAB missions, only SOLRAD/GRAB 1 and SOLRAD 3/GRAB 2 were successes, the others failing to reach orbit. In 1962, all U.S. overhead reconnaissance projects were consolidated under the National Reconnaissance Office (NRO), which elected to continue and expand the GRAB mission starting July 1962 [2] with a next-generation set of satellites, code-named POPPY.[5] With the initiation of POPPY, SOLRAD experiments would no longer be carried on electronic spy satellites; rather, they would now get their own satellites, launched alongside POPPY missions to provide some measure of mission cover.[13] Starting with SOLRAD 8, launched in November 1965, the final five SOLRAD satellites were scientific satellites launched singly, three of which were also given NASA Explorer program numbers. The last in this final series of SOLRAD satellites flew in 1976. In all, there were thirteen operational satellites in the SOLRAD series.[8] The GRAB program was declassified in 1998.[21]
Explorer 1 was the first satellite launched by the United States in 1958 and was part of the U.S. participation in the International Geophysical Year (IGY). The mission followed the first two satellites, both launched by the Soviet Union during the previous year, Sputnik 1 and Sputnik 2. This began a Space Race during the Cold War between the two nations.
Vanguard 1 is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. It was launched 17 March 1958. Vanguard 1 was the first satellite to have solar electric power. Although communications with the satellite were lost in 1964, it remains the oldest human-made object still in orbit, together with the upper stage of its launch vehicle.
Project Vanguard was a program managed by the United States Navy Naval Research Laboratory (NRL), which intended to launch the first artificial satellite into low Earth orbit using a Vanguard rocket. as the launch vehicle from Cape Canaveral Missile Annex, Florida.
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).
Explorer 7 was a NASA satellite launched on 13 October 1959, at 15:30:04 GMT, by a Juno II launch vehicle from Cape Canaveral Air Force Station (CCAFS) to an orbit of 573 × 1,073 km (356 × 667 mi) and inclination of 50.27°. It was designed to measure solar X-ray and Lyman-alpha flux, trapped energetic particles, and heavy primary cosmic rays. Secondary objectives included collecting data on micrometeoroid penetration, molecular sputtering and studying the Earth-atmosphere heat balance.
The Solar Radiation and Climate Experiment (SORCE) was a NASA-sponsored satellite mission that measured incoming X-ray, ultraviolet, visible, near-infrared, and total solar radiation. These measurements specifically addressed long-term climate change, natural variability, atmospheric ozone, and UV-B radiation, enhancing climate prediction. These measurements are critical to studies of the Sun, its effect on the Earth's system, and its influence on humankind. SORCE was launched on 25 January 2003 on a Pegasus XL launch vehicle to provide NASA's Earth Science Enterprise (ESE) with precise measurements of solar radiation.
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 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.
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.
The SOLRAD 8,Explorer 30 or SE-A satellite was one of the NASA SOLRAD program that began in 1960 to provide continuous coverage of solar radiation with a set of standard photometers. SOLRAD 8 was a spin-stabilized satellite oriented with its spin axis perpendicular to the sun-satellite line so that the 14 solar X-ray and ultraviolet photometers pointing radially outward from its equatorial belt viewed the sun on each revolution. Data were transmitted in real time by means of an FM / AM the satellite's telemetry system and were recorded by the stations on the Spacecraft Tracking and Data Acquisition Network (STADAN) tracking network.
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. 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.
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.
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.
References
1 2 "SOLRAD 1 1960-007B". NASA. 14 May 2020. Retrieved 15 January 2021. This article incorporates text from this source, which is in the public domain.
↑ 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. The National Academies Press. p.157. doi:10.17226/11299. ISBN978-0-309-18120-4. Archived from the original on 7 January 2019. Retrieved 6 January 2019. This article incorporates text from this source, which is in the public domain.
↑ Benedict, Howard (22 June 1960). "Single Rocket Puts Two Satellites in Orbit". Alabama Journal. Montgomery, Alabama. Associated Press. p.6. Archived from the original on 8 April 2019. Retrieved 8 April 2019– via Newspapers.com.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated in underline. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).
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