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The SOLRAD 1 (also known as GREB 1) spin-stabilized spacecraft was a sphere of 51 cm diameter that was put into orbit by the same launch vehicle that launched Transit 2A. The spacecraft carried two Lyman-alpha photometers and one X-ray photometer mounted along the equator of the satellite, looking out in a direction parallel to its equatorial plane. A visible light aspect system that used a vacuum photocell to determine the solar aspect angle was also attached. The aspect system had the same direction of view as the UV photometers and the opposite view with respect to the X-ray photometer. The objective of the project was to make long-term continuous observations of the solar hydrogen Lyman-alpha and soft X-ray emissions and to correlate these emissions with ground-based observations.

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.

Launch took place from Cape Canaveral on a Thor booster on 22 June 1960 at 6:00 UT. The SOLRAD 1 satellite was mounted on top of the Transit 2A satellite, as pictured, to be separated at deployment. Image credit: National Museum of the U.S. Navy

Alternate Names

  • 00046
  • 1960 Eta 2
  • GRAB 1
  • GREB 1
  • SR 1
  • Sunray 1

Facts in Brief

Launch Date: 1960-06-22
Launch Vehicle: Thor
Launch Site: Cape Canaveral, United States
Mass: 19.05 kg

Funding Agency

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


  • Solar Physics

Additional Information

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



NameRoleOriginal AffiliationE-mail
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