SOLRAD 7A

Mission type| Solar X-Ray
Operator| NRL
Spacecraft properties
Launch mass| 45.4 kilograms (100 lb)
Start of mission
Launch date| January 11, 1964, 5:00:00 (1964-01-11UTC05Z) UTC
Rocket| Thor Augmented Delta-Agena D
Launch site| Vandenberg Air Force Base Space Launch Complex 3, Pad 5
End of mission
Last contact| Feb. 5, 1965 (usable data); July 1966 (contact)
Orbital parameters
Reference system| Geocentric
Regime| Low Earth
Perigee altitude| 903 kilometers (561 mi)
Apogee altitude| 926 kilometers (575 mi)
Inclination| 69.9°
Period| 103.30 minutes

SOLRAD

<- SOLRAD 6

SOLRAD 7B ->

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.

## Contents

* 1 History
* 2 Spacecraft
* 3 Mission and results
* 4 Legacy and status
* 5 See also
* 6 References

## History

The SOLRAD science satellite program was conceived in 1958 to observe the Sun in the X-ray spectrum. It was quickly combined, to provide civilian cover (launches being unclassified at that time),[1] with the concurrently conceived United States Naval Research Laboratory's GRAB satellite project,[2] which would collect information on foreign radars and communications installations.[3] There were five SOLRAD/GRAB missions between 1960 and 1962, with the scientific SOLRAD experiments sharing satellite space with GRAB's intelligence payload. Two of the missions were successful.[2]

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[4] 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.[6]

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 (satellite) ionospheric research satellite.[6] The mission was successful, despite POPPY 1's elliptical (rather than the planned circular) orbit, and data was returned for 28 months.[7] No SOLRAD was launched concurrent with this first POPPY mission.[2]

SOLRAD 6, the first of the second-generation SOLRADs, was launched alongside POPPY 2 on June 15, 1963,[6] but decayed into the atmosphere on August 1, 1963, returning little data.[2]

## Spacecraft

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 measurements back to Earth.[8]

## Mission and results

Launched on January 11, 1964, along with four other spacecraft aboard a Thor Augmented Delta-Agena D,[9] (including POPPY 3, an electronic signals intelligence (ELINT) surveillance package[6]) its orbit was nearly circular at 900 kilometers (560 mi). 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.[8]

SOLRAD 7A transmitted data in real time on 136 MHz, providing 10 to 20 minutes 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.[8] Dubbed "SOLRAD 6" by several sources,[10]: 68 the satellite reported comparatively low solar X-ray emission levels during its time in orbit.[11] After February 5, 1965, no usable data were obtained from the satellite, although it continued operating until July 1966.[12]

From SOLRAD 7A data, it was concluded that the X-ray region of the solar corona was a series of small cells that flared and decayed rapidly, emitting hard X-rays in the process. This dramatically change previous models: Earthbound telescopes had only been able to detect the very hot, flashing gas those cells created, the net result making the corona seem a homogeneous region extending 1,000,000 miles (1,609,344 km) from the Sun.[13]

The operational period of the satellite allowed it to contribute to the International Quiet Solar Year, an international scientific program mounted to gather information about the Sun during the nadir of its 11-year luminosity cycle (Jan. 1, 1964, through Dec. 31, 1965).[14] SOLRAD 7A data indicated that the Sun's X-ray output was at a minimum during May, June and July 1964.[13]

## Legacy and status

The satellite is still in orbit and its position can be tracked online.[15]

COSPAR satellite ID: 1964-001D[8]

## See also

## References

1. ↑ 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 1-56098-830-4.
2. ↑ 2.0 2.1 2.2 2.3 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. https://books.google.com/books?id=2ZNxDwAAQBAJ&pg=PA300.
3. ↑ Parry, Daniel (October 2, 2011). "NRL Center for Space Technology Reaches Century Mark in Orbiting Spacecraft Launches". U.S. Naval Research Laboratory. https://www.nrl.navy.mil/Media/News/releases/nrl-center-space-technology-reaches-century-mark-orbiting-spacecraft-launches/.
4. ↑ "Review and Redaction Guide". National Reconnaissance Office. 2008. https://fas.org/irp/nro/review-2008.pdf.
5. ↑ "History of the Poppy Satellite System". National Reconnaissance Office. 2006-08-14. http://www.theblackvault.com/documents/spysatellites/PoppySatellite.pdf.
6. ↑ 6.0 6.1 6.2 6.3 McDowell, Jonathan. "Launch Log". http://planet4589.org/space/log/launchlog.txt.
7. ↑ Day, Dwayne A.. "A flower in the polar sky: the POPPY signals intelligence satellite and ocean surveillance". http://www.thespacereview.com/article/1115/1.
8. ↑ 8.0 8.1 8.2 8.3 "SOLRAD 7A". https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1964-001D.
9. ↑ "Astronautics and Aeronautics, 1964". Washington, D.C.: NASA. 1965. https://history.nasa.gov/AAchronologies/1964.pdf.
10. ↑ Significant Achievements in Solar Physics 1958–1964. Washington D.C.: NASA. 1966. OCLC 860060668.
11. ↑ "The 44-60 Å Flux During the Ascending Period of the Solar Cycle No. 20 (1964-67)". pp. 546–550. http://adsabs.harvard.edu/full/1968SoPh....5..546L.
12. ↑ 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. doi:10.1007/BF00149895. Bibcode: 1991SoPh..133..371K.
13. ↑ 13.0 13.1 "Aeronautics and Astronautics, 1965". Washington, D.C.: NASA. 1966. p. 10. https://history.nasa.gov/AAchronologies/1965.pdf.
14. ↑ "Encyc. Britannica online, Mar. 2, 2005 (citation by LOC)". http://id.loc.gov/authorities/subjects/sh85067461.html.
15. ↑ "SOLRAD 7A - NORAD 730 - 3D Online Satellite Tracking". http://www.satflare.com/track.asp?q=00730#TOP.

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Orbital launches in 1964

Poppy 3 * GGSE-1 * SOLRAD 7A * SECOR 1 | OPS 3367A * OPS 3367B | Relay 2 | Echo 2 | Jupiter Nosecone | Elektron 1 * Elektron 2 | Ranger 6 | OPS 3444 | Zond 3MV-1 No.2 | Kosmos 25 | OPS 2423 | OPS 3722 | OPS 3435 | Kosmos 26 | BE-A | Luna E-6 No.6 | OPS 3467 | Kosmos 27 | Ariel 2 | Zond 1 | Kosmos 28 | Gemini 1 | Polyot 2 | Luna E-6 No.5 | Transit 5BN-3 * Transit 5E-4 | OPS 3743 | Kosmos 29 | OPS 2921 | Kosmos 30 | OPS 3592 | Apollo AS-101 | OPS 4412 | OPS 3483 | Molniya-1 No.2 | Kosmos 31 | Kosmos 32 | OPS 3236 | OPS 4467A * OPS 4467B | OPS 3754 | Kosmos 33 | ESRS | Atlas-Centaur 3 | Kosmos 34 | OPS 3395 | OPS 3684 * OPS 4923 | Elektron 3 * Elektron 4 | OPS 3491 | Kosmos 35 | OPS 3662 * OPS 3674 * ERS-13 | Ranger 7 | Kosmos 36 | OPS 3042 | Kosmos 37 | OPS 3802 * OPS 3216 | Kosmos 38 * Kosmos 39 * Kosmos 40 | Syncom 3 | OPS 2739 | Kosmos 41 | Kosmos 42 * Kosmos 43 | Kosmos 44 | Titan 3A-2 | OGO-1 | Kosmos 45 | OPS 3497 | Apollo AS-102 | OPS 4262 | Kosmos 46 | Explorer 21 | OPS 3333 | Kosmos 47 | OPS 5798 * Dragsphere 1 * Dragsphere 2 | OPS 4036 | Explorer 22 | Voskhod 1 | Kosmos 48 | OPS 3559 | Strela-1 No.6 * Strela-1 No.7 * Strela-1 No.8 | OPS 4384 * OPS 5063 | Kosmos 49 | Kosmos 50 | OPS 5434 | OPS 3062 | Mariner 3 | Explorer 23 | OPS 3360 | Explorer 24 * Explorer 25 | Mariner 4 | Zond 2 | DS-2 No.2 | OPS 4439 | Kosmos 51 | Titan 3A-1 | Surveyor Mass Model | OPS 6582 * Transit 5E-5 | San Marco 1 | OPS 3358 | Explorer 26 | OPS 3762

Payloads are separated by bullets ( * ), launches by pipes ( | ). Crewed flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.

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