THE COBE MISSION - ITS DESIGN AND PERFORMANCE 2 YEARS AFTER LAUNCH

COBE, NASA's first space mission devoted primarily to cosmology, carries three scientific instruments to make precise measurements of the spectrum and anisotropy of the cosmic microwave background radiation on angular scales greater than 7-degrees and to conduct a search for a diffuse cosmic infrared background radiation with 0.7-degrees angular resolution. The mission goal is to make these measurements to the limit imposed by the local astrophysical foregrounds. The COBE instruments cover the wavelength range from 1.2 mum to 1 cm. The instruments are calibrated periodically in orbit using internal calibrators and celestial standards. The observing strategy is designed to minimize and allow determination of systematic errors that could result from spacecraft operations, the local environment of the spacecraft, and emission from foreground astrophysical sources such as the Galaxy and the solar system. The mission orbit and the scanning techniques provide full sky coverage, while simultaneously minimizing solar and terrestrial radiation on the instruments and reducing thermal and radiative perturbations of the measurements. The three instruments are complementary in that combined data from all are needed to discriminate cosmological emissions from other astrophysical sources. Operational experience after launch shows that flight performance generally meets or exceeds the design goals. COBE has now completed 2 years of flight operations, and a third year has been initiated. Initial COBE data products are planned for release in 1993 June.