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Injun 1



The satellite Injun 1 was the first of a series of spacecraft designed and built by the University of Iowa to study the natural and artificial trapped radiation belts, auroras and airglow, and other geophysical phenomena. Injun 1 was launched simultaneously with Transit 4A and Greb 3 (SOLRAD 3). Transit 4A successfully separated from Injun 1, but Greb 3 did not. Injun 1 was designed to be magnetically aligned. However, due to the presence of Greb 3 (which blocked the view of the photometer), it was impossible to keep the satellite constantly oriented on the terrestrial magnetic field throughout an orbit. A single axis fluxgate magnetometer was used to monitor the orientation of the spacecraft with respect to the local magnetic field. Injun 1 had a complex spin-and-tumble motion with an ill-defined and variable period of several minutes. The satellite sent back radiation data until March 6, 1963, and is expected to be in orbit for about 900 yr.

The GREB program was classified at the time, the primary purpose was to receive signals from Soviet radar installations to learn about their air defense posture. The data were used by the U.S. Strategic Air Command. As a cover story, the satellites were equipped with instruments to measure solar radiation. Sometimes referred to as Galactic Radiation and Background (GRAB) satellites, or as part of the SOLar RADiation (SOLRAD) program, they were publicized as scientific missions, and did in fact return scientific data.

Image courtesy of the University of Iowa.

Alternate Names

  • 1961 Omicron 2
  • 00117
  • SOLRAD 3
  • Injun-SR-3
  • GREB 3
  • Injun1
  • GRAB 3

Facts in Brief

Launch Date: 1961-06-29
Launch Vehicle: Thor
Launch Site: Cape Canaveral, United States
Mass: 16 kg

Funding Agencies

  • University of Iowa (United States)
  • Department of Defense-Department of the Navy (United States)


  • Space Physics

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. H. Kent Hills



NameRoleOriginal AffiliationE-mail
Prof. James A. Van AllenProject ManagerUniversity of Iowa
Dr. Brian J. O'BrienProject ScientistDepartment of Environmental
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