Diffuse Microwave Emission Survey
  The Diffuse Microwave Emission Survey (DIMES) has been selected for a mission concept study for NASA's New Mission Concepts for Astrophysics program. DIMES will measure the frequency spectrum of the cosmic microwave background and diffuse Galactic foregrounds at centimeter wavelengths to 0.1% precision (0.1 mK), and will map the angular distribution to 20 muK per 6 degree field of view. It consists of a set of narrow-band cryogenic radiometers, each of which compares the signal from the sky to a full-aperture blackbody calibration target. All frequency channels compare the sky to the same blackbody target, with common offset and calibration, so that deviations from a blackbody spectral shape may be determined with maximum precision. Measurements of the CMB spectrum complement CMB anisotropy experiments and provide information on the early universe unobtainable in any other way; even a null detection will place important constraints on the matter content, structure, and evolution of the universe. Centimeter-wavelength measurements of the diffuse Galactic emission fill in a crucial wavelength range and test models of the heat sources, energy balance, and composition of the interstellar medium. 
Al Kogut (HSTX/GSFC)