|Mission type||Solar X-Ray|
|Launch mass||45.4 kg|
|Start of mission|
|Launch date||11 January 1964, 5:00:00UTC|
|Rocket||Thor Augmented Delta-Agena D|
|Launch site||Vandenberg AFB|
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. There were five SOLRAD/GRAB missions between 1960–62, two of which were successful.
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 with a next-generation set of satellites, code-named POPPY.
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. The mission was successful, despite POPPY 1's elliptical (rather than the planned circular) orbit, and data was returned for 28 months. However, POPPY 1 does not appear to have been a SOLRAD mission. The next three POPPY satellites were equipped with SOLRAD experiment packages.
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.
Mission and results
Launched on January 11, 1964 along with four other spacecraft aboard a Thor Augmented Delta-Agena D, 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.
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. Dubbed "SOLRAD 6" by several sources,:68 the satellite reported comparatively low solar X-ray emission levels during its time in orbit.
The satellite is still in orbit and its position can be tracked online.
COSPAR satellite ID: 1964-001D
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