The Wilkinson Microwave Anisotropy Probe (WMAP) is a spacecraft measuring variations (Anisotropy) in the Cosmic Microwave Background. WMAP was launched in 2001 and is still active (July 2013), located at the L2 Earth/Sun Lagrangian Point. WMAP data is used for Cosmology research. COBE had the same mission earlier, but to less detail, and Planck is a newer similar mission.
Results were released on two-year intervals, the first (WMAP1) released in 2005 with a year's data, through the final 9-year results (WMAP9) released in 2011.
Goddard Space Flight Center (GSFC)