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COBE (Explorer 66)


The purpose of the COBE (Cosmic Background Explorer) mission was to take precise measurements of the diffuse radiation between 1 micrometer and 1 cm over the whole celestial sphere. The following quantities were measured:

  • the spectrum of the 3 K radiation over the range 100 micrometers to 1 cm;
  • the anisotropy of this radiation from 3 to 10 mm; and,
  • the spectrum and angular distribution of diffuse infrared background radiation at wavelengths from 1 to 300 micrometers.

The experiment module contained the instruments and a dewar filled with 650 liters of 1.6 K liquid helium, with a conical sun shade. The base module contained the attitude control, communications and power systems. The satellite rotated at 1 rpm about the axis of symmetry to control systematic errors in the anisotropy measurements and to allow observations of the zodiacal light at various solar elongation angles. The orientation of the spin axis was maintained anti-earth and at 94 degrees to the sun-earth line. The operational orbit was dawn-dusk sun-synchronous so that the sun was always to the side and thus was shielded from the instruments. With this orbit and spin-axis orientation, the instruments performed a complete scan of the celestial sphere every six months.

The spacecraft featured three instruments:

  • Far Infrared Absolute Spectrophotometer (FIRAS) to compare the spectrum of the cosmic microwave background radiation with a precise blackbody,
  • Differential Microwave Radiometer (DMR) to map the cosmic radiation sensitively, and
  • Diffuse Infrared Background Experiment (DIRBE) to search for the cosmic infrared background radiation.

The Instruments were housed inside a cryostat, cooled with 95.7 kg liquid helium.

Instrument operations were terminated 1993-12-23. As of January 1994, engineering operations were to conclude that month, after which operation of the spacecraft would be transferred to Wallops for use as a test satellite.

Nation: USA
Type / Application: Cosmology
Operator: NASA
Contractors: NASA Goddard Space Flight Center, Ball Aerospace
Equipment: FIRAS, DMR, DIRBE, Cryostat
Configuration: Hexaginal prism, 3 solar arrays, deployable sunshade
Propulsion: ?
Power: 3 deployable fixed solar arrays, batteries
Mass: 2265 kg
Orbit: 872 km × 886 km, 99.0
Satellite COSPAR Date LS Launch Vehicle Remarks
COBE (Explorer 66) 1989-089A 18.11.1989 Va SLC-2W Delta-5920


  • NSSDC Master Catalog: COBE
Further Explorer missions:

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