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AKA: Cosmic Background Explorer. Status: Operational 1989. First Launch: 1989-11-18. Last Launch: 1989-11-18. Number: 1 . Gross mass: 2,265 kg (4,993 lb). Height: 5.49 m (18.01 ft).
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.
NASA NSSDC Master Catalog Description
The purpose of the Cosmic Background Explorer (COBE) 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: (1) the spectrum of the 3 K radiation over the range 100 micrometers to 1 cm; (2) the anisotropy of this radiation from 3 to 10 mm; and, (3) 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.
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.