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This solar X-ray monitoring satellite was launched in January 1964. It was equipped with ionization chambers to cover the ranges 1-8 A, 8-12 A, and 44-60 A. It was placed into orbit by an Agena D launch vehicle, with its spin axis roughly perpendicular to the sun-satellite direction with an initial spin rate of about 2 cps. The satellite was constructed so that the moments of inertia favored stable rotation about the spin axis; however, the magnetic brooms produced varying torques by interacting with the earth's magnetic field. This resulted in a slow precession of the spin axis. The orbit was nearly circular at 900 km and each pass provided 10 to 20 min of data at a ground station. 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 A) and the low-frequency portion of the solar hydrogen Lyman-alpha emission spectrum (1225 to 1350 A), and to transmit these quantitative analog data back to earth. Data were transmitted in real time on 136 Mc per second, and several European observatories successfully recorded the telemetry. The satellite transmitted data continuously until September 1964 from all but the 44- to 55-A and 8- to 16-A detectors, both of which failed soon after launch. Sporadic data were received until February 1965. For more details, see R. W. Kreplin, Space Res., v. 5, p. 951, 1964.

Alternate Names

  • GREB 5
  • 00730

Facts in Brief

Launch Date: 1964-01-11
Launch Vehicle: Thrust Augmented Thor-Agena D
Launch Site: Vandenberg AFB, United States
Mass: 45.4 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



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