page_title: SOLRAD 3
section_title: Mission and science results
hierarchical_section_title: SOLRAD 3 / Mission and science results
context_page_description: SOLRAD 3 was a solar X-Ray satellite and electronic surveillance satellite, the third in the SOLRAD program. Developed by the United States Navy's Naval Research Laboratory, it shared satellite space with and provided cover for the Navy's GRAB 2, a secret electronic surveillance program.
  The satellite was launched atop a Thor DM-21 Ablestar rocket on June 29, 1961 along with Transit 4A and the University of Iowa's Van Allen Belts Injun 1 satellite. After reaching orbit, SOLRAD 3/GRAB 2 and INJUN 1 separated from Transit 4A but not from each other. Though this reduced SOLRAD 3's data-transmission ability by half, nevertheless, the satellite still returned valuable information regarding the sun's normal levels of X-ray emissions. The SOLRAD experiment package also established that, during solar flares, the higher the energy of emitted X-rays, the more disruption caused on the Earth's thermosphere. The GRAB mission was also highly successful, returning so much data on Soviet air defense radar facilities that an automated analysis system had to be developed to process it all.
context_section_description: SOLRAD 3/GRAB 2 was launched on June 29, 1961 at 04:22 UTC on a Thor DM-21 Ablestar rocket, along with Transit 4A and the University of Iowa's Van Allen Belts Injun 1 satellite from Cape Canaveral pad LC17B.  Its course to orbit was more northerly than that of its predecessors to avoid the possibility of fragments falling on Cuba in the event of a mission failure (as had happened with SOLRAD 2).
  After reaching orbit, SOLRAD 3/GRAB 2 and INJUN 1 separated from Transit 4A but not from each other, causing them to rotate more slowly than planned.  Moreover, because electro-magnetic interference generated by the spacecraft prevented ground controllers from requesting data from both spacecraft at the same time, SOLRAD 3/GRAB 2's transmissions were limited to odd-numbered days, INJUN's to even-numbered days; thus, data was only recovered for half of each satellite's lifetime.
  Nevertheless, the SOLRAD package on the satellite made several important findings.   It established the Sun's normal X-ray radiation levels during times of inactivity at levels below 14Å in wavelength (less than 5×10⁻³ ergs/cm²/sec).  The satellite also found that the higher the hardness (energy level) of X-rays emitted during solar flares, the greater the disturbances and microwave bursts in the thermosphere, both affecting radio communications.
caption: SOLRAD 3's Thor Able Star takes off.
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