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Thor SLV-2A Agena D with Composite-4 (Jan. 11 1964).gif
Mission typeSolar X-Ray
COSPAR ID1964-001D
SATCAT no.00730Edit this on Wikidata
Spacecraft properties
Launch mass45.4 kg
Start of mission
Launch date11 January 1964, 5:00:00 (1964-01-11UTC05Z) UTC
RocketThor Augmented Delta-Agena D
Launch siteVandenberg AFB
Orbital parameters
Reference systemGeocentric
RegimeLow Earth

SOLRAD 7A was the seventh solar X-Ray monitoring satellite in the SOLRAD series, and the fourth to actually orbit the Earth. One of the second-generation Solrads, it was a stand-alone scientific satellite launched into orbit along with four other military satellites atop a Thor Augmented Delta-Agena D rocket.


The SOLRAD X-ray science satellite program was originally developed as civilian cover for and co-flyers with the United States Naval Research Laboratory's GRAB satellites, which were built to collect information on foreign radar and communications installations.[1] There were five SOLRAD/GRAB missions between 1960–62, two of which were successful.[2]

In 1962, all U.S. overhead reconnaissance projects were consolidated under the National Reconnaissance Office (NRO), which elected to continue the SOLRAD and GRAB mission beginning in July 1962[3] with a next-generation set of satellites, code-named POPPY.[4]

The first POPPY mission was launched on December 13, 1962, along with several other satellites on a mission similar to that of SOLRAD 3, complete with an Injun ionospheric research satellite.[5] The mission was successful, despite POPPY 1's elliptical (rather than the planned circular) orbit, and data was returned for 28 months.[6] However, POPPY 1 does not appear to have been a SOLRAD mission. The next three POPPY satellites were equipped with SOLRAD experiment packages.[2]

SOLRAD 6 co-flew with POPPY 2 on June 15, 1963, but decayed into the atmosphere on August 1, 1963, returning little data.[2]


SOLRAD 7A was equipped with ionization chambers to monitor solar X-Rays in the wavelength ranges of 1-8 Å, 8-12 Å, and 44-60 Å. This satellite contained five X-ray photometers, four UV photometers, and two systems to accurately determine the solar aspect angle. Its purposes were to monitor the soft component of solar X-rays (2 to 60 Å) and the low-frequency portion of the solar hydrogen Lyman-alpha emission spectrum (1225 to 1350 Å), and to transmit these quantitative analog data back to earth.[7]

Mission and results[edit]

Launched on January 11, 1964 along with four other spacecraft aboard a Thor Augmented Delta-Agena D,[8] its orbit was nearly circular at 900 km. SOLRAD 7A's spin axis was roughly perpendicular to the sun-satellite direction with an initial spin rate of about two revolutions per second; however, the magnetic brooms produced varying torques by interacting with the earth's magnetic field resulting in a slow precession of the spin axis.[7]

SOLRAD 7A transmitted data in real time on 136 MHz, providing 10 to 20 min of data at a pass to ground stations. The satellite's 44- to 55-Å and 8- to 16-Å detectors both failed soon after launch, but data was continuously returned from its other instruments until September 1964. Sporadic data were received until February 1965. In addition to the intended recipients, several European observatories successfully recorded the telemetry.[7] Dubbed "SOLRAD 6" by several sources,[9]:68 the satellite reported comparatively low solar X-ray emission levels during its time in orbit.[10]

The satellite is still in orbit and its position can be tracked online.[11]

COSPAR satellite ID: 1964-001D[7]

See also[edit]


  1. ^ "Navy's Needs in Space for Providing Future Capabilities". Retrieved January 6, 2019.
  2. ^ a b c American Astronautical Society (23 August 2010). Space Exploration and Humanity: A Historical Encyclopedia [2 volumes]: A Historical Encyclopedia. Santa Barbara, Calif: ABC-CLIO. pp. 300–303. ISBN 978-1-85109-519-3.
  3. ^ "National Reconnaissance Office Review and Redaction Guide" (PDF). Retrieved January 24, 2019.
  4. ^ "History of the Poppy Satellite System" (PDF). National Reconnaissance Office. 2006-08-14. Retrieved 2010-02-28.
  5. ^ McDowell, Jonathan. "Launch Log". Retrieved 2018-12-30.
  6. ^ Day, Dwayne A. "A flower in the polar sky: the POPPY signals intelligence satellite and ocean surveillance". Retrieved February 17, 2019.
  7. ^ a b c d "SOLRAD 7A". Retrieved January 2, 2019.
  8. ^ "Astronautics and Aeronautics, 1964" (PDF). Retrieved 2018-12-30.
  9. ^ Significant Achievements in Solar Physics 1958–1964. Washington D.C.: NASA. 1966. OCLC 860060668.
  10. ^ "THE 44-60 Å FLUX DURING THE ASCENDING PERIOD OF THE SOLAR CYCLE No. 20 (1964-67)". Solar Physics. pp. 546–550. Retrieved March 5, 2019.
  11. ^ "SOLRAD 7A - NORAD 730 - 3D Online Satellite Tracking". Retrieved January 2, 2019.