The Cosmic Background Explorer's observations of diffuse cosmic background radiation helped answer basic questions such as whether the matter in the universe was homogeneously distributed, whether the universe was uniformly expanding and rotating, and how and when stars and galaxies first formed. COBE also mapped interstellar and interplanetary dust clouds.

Originally planned for launch on the Shuttle, COBE was redesigned for launch aboard a Delta 2 following the Challenger disaster. COBE's supply of liquid helium was exhausted in September 1990, causing loss of the FIRAS instrument.

The spacecraft was spin stabilized (0.8 rpm about sunline) using 3 reaction wheels and torque rods. Attitude control knowledge (4 arcmin) was provided by magnetometers, earth sensors, sun sensors, gyros. The satellite consisted of a hexagonal spacecraft bus and a cryostat containing 95.7 kg of liquid helium for cooling sensors. This was protected against solar and terrestrial radiation by a conical shield. Deployable solar panels provided 1050W BOL. Downlink was through the TDRSS relay satellite.

The instrument payload consisted of the Differential Microwave Radiometer (DMR) to check the thermal and structural uniformity of the early universe, the Far Infrared Absolute Spectrometer (FIRAS) and the Diffuse IR Background Experiment (DIRBE), to search for the remnant radiation emitted from the primordial galaxies as they formed.

Design Life: 1 year. Typical orbit: 887 x 898 km, incl. = 99.0 degree, sun synchronous. Length: 5.49 m (18.01 ft). Maximum Diameter: 2.44 m (8.00 ft). Mass: 2,265 kg (4,993 lb). Associated Launch Vehicle: Delta 5000.

• 1989 November 18 - COBE - Launch Site: Vandenberg. Launch Vehicle: Delta 5000. Mass: 2,265 kg (4,993 lb). Perigee: 873 km (542 mi). Apogee: 886 km (550 mi). Inclination: 98.90 deg. Period: 102.60 min.

  Cosmic Background Explorer; measured background galactic infrared radiation. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

• 1990 September 1 - COBE's liquid helium supply exhausted -

  The Cosmic Background Explorer's supply of liquid helium was exhausted, causing loss of the FIRAS (Far Infrared Absolute Spectrometer) instrument.

• McDowell, Jonathan, Launch Log, October 1998. Jonathan McDowell's complete on-line listing of all objects orbited since Sputnik. Accessed at: http://hea-www.harvard.edu/~jcm/space/log/launch.html.

• JPL Mission and Spacecraft Library, Jet Propulsion Laboratory, 1997. Accessed at: http://msl.jpl.nasa.gov/home.html.

• McDowell, Jonathan, Jonathan's Space Home Page, Harvard University, 1997-present. Jonathan McDowell's complete on-line listing of all objects orbited and over 20,000 rocket launches Accessed at: http://www.planet4589.org/jsr.html.

• Krebs, Gunter, Gunter's Space Page, University of Frankfurt, 1996. Accessed at: http://www.skyrocket.de/space.

• USAF Satellite Database, USAF Institute of Technology, 1995. Accessed at: ftp://archive.afit.af.mil/pub/space/.