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Uhuru (SAS-A) was the first in the series of small spacecraft whose objectives were to survey the celestial sphere and search for sources radiating in the X-ray, gamma-ray, UV, and other spectral regions. The primary mission of Uhuru was to develop a catalog of celestial X-ray sources by systematic scanning of the celestial sphere in the energy range from 2-20 keV.

The spacecraft was launched 12 December 1970 from the San Marco platform off the coast of Kenya, Africa, into a near-circular equatorial orbit. The orbiting spacecraft was in the shape of a cylinder approximately 56 cm in diameter and 116 cm in length. Four solar paddles were used to recharge a 6 amp-h, eight-cell, nickel-cadmium battery, and to provide power to the spacecraft and experiment. The spacecraft was stabilized by an internal wheel, and a magnetically torqued commandable control system was used to point the spin axis of the spacecraft to any point of the sky. The aspect sensing system consisted of both a star and sun sensor that shared the same processing electronics. The system was designed with heavy emphasis on redundancy, not only in the more obvious areas such as aspect sensors and high- and low-voltage power supplies, but also in signal switching and high-voltage distribution. The resulting instrument was capable of sustaining several simultaneous major failures without seriously compromising the scientific objectives. Data were stored on a one-orbit storage tape recorder and telemetered during a 3.4 minute playback cycle. A 1000 bps PCM/PM system was used.

Alternate Names

  • SAS-A
  • SAS 1
  • Explorer 42
  • PL-701C
  • 04797

Facts in Brief

Launch Date: 1970-12-12
Launch Vehicle: Scout
Launch Site: San Marco Platform, Kenya
Mass: 141.5 kg
Nominal Power: 9.6 W

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Astronomy

Additional Information

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



NameRoleOriginal AffiliationE-mail
Mrs. Marjorie R. TownsendProject ManagerNASA Goddard Space Flight Center
Dr. Carl E. FichtelProject ScientistNASA Goddard Space Flight
Mr. John R. HoltzProgram ManagerNASA Headquarters
Dr. Nancy G. RomanProgram ScientistNASA Headquarters

Selected References

  • Mullens, D. G., Automated testing of the SAS-A experiment, IEEE Trans. Instrum. Meas., IM-20, 235-238, doi:10.1109/TIM.1971.5570646, Nov. 1971.
  • Jagoda, N., et al., The Uhuru X-ray instrument, IEEE Trans. Nucl. Sci., 19, No. 1, 579-591, doi: 10.1109/TNS.1972.4326562, Feb. 1972.

Related Information/Data at NSSDCA


US Active Archive for Uhuru Information/Data

The Uhuru Archive at HEASARC

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