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ERS 18



The primary objectives of this spacecraft were to (1) make a measurement of the cosmic gamma-ray spectrum between 0.25 and 6 MeV, (2) monitor the solar x-ray flux in the 1 to 14-A and above 25 KeV ranges, (3) obtain a background measurement for a prototype detector for the measurement of delayed gamma-rays from a space nuclear detonation, and (4) measure charged particles within the magnetosphere in the energy ranges 40 to 400 KeV for electrons, 0.38 to 25 MeV for protons, and 2.6 to 6 MeV for alpha particles. The spacecraft was a spin stabilized regular octahedron that weighed 7.8 kg and measured 29.3 cm along each triangular edge. Each of the eight triangular faces contained 102 n-on-p 10-ohm-cm solar cells, and the total average power output was about 4 w. The spin rate was initially about 6 rpm. However, there was a large coning during the early lifetime, and owing to improper dynamic balancing, the final stable spin axis was nearly 90 deg different from the intended one. This change of orientation had only a minor effect on the data interpretation. The experiment complement consisted of three GM tubes, one plastic scintillation counter, one lithium drifted silicon detector, one surface barrier detector, one heavily shielded sodium iodide detector, and a large sodium iodide detector shielded by a plastic guard counter. These instruments charged particles, x-rays, gamma-rays, and cosmis rays in the near-earth environment. Most of the detector signals were converted to analog voltages by logatithmic count rate meters and were transmitted over irig channel 5 with a PAM/FM/FM system that radiated about 1 w of RF power. Thirty different measurements, including housekeeping data, were time commutated by a 16-channel commutator which had two segments subcommutated eigth times. Each main commutator segment was sampled for 4.7 sec, and the response of the overall system was limited by a 0.047-sec low pass filter in the subcarrier oscillator. Several low counting rate channels were converted to a quasi-digital format before sampling. The antenna was a conventional half-wavelength dipole fabricated from 1/2-in.-wide ribbon steel which self-erected from a coiled position and projected unsupported from the satellite. Temperature control was achieved by passive techniques. The spacecraft also contained a solar aspect sensor system to determine tha angle between the satellite-sun line and the satellite spin axis to within 7.5 deg. The spacecraft operated successfully from launch until June 3, 1968, when a preset timer turned off the transmitter.

Alternate Names

  • ORS 4
  • 02767
  • ORS 3(B)
  • ERS18
  • 1967-040C

Facts in Brief

Launch Date: 1967-04-28
Launch Vehicle: Titan III-C
Launch Site: Cape Canaveral, United States
Mass: 9.1 kg

Funding Agency

  • Department of Defense-Department of the Air Force United States


  • Space Physics
  • Astronomy

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. Harold E. AdelsonProject ManagerTRW Systems Group
Dr. Louis S. WalterProject ScientistNASA Goddard Space Flight Center
Mr. R. J. MartinProject EngineerTRW Systems Group
Dr. James I. VetteProgram ScientistNASA Goddard Space Flight Center
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