  SPOrt is an ASI-funded experiment specifically designed to measure the sky
polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be
flown on the International Space Station. Starting in 2006 and for at least 18
months, it will be taking direct and simultaneous measurements of the Stokes
parameters Q and U at 660 sky pixels, with FWHM=7 degrees. Due to development
efforts over the past few years, the design specifications have been
significantly improved with respect to the first proposal. Here we present an
up-to-date description of the instrument, which now warrants a pixel
sensitivity of 1.7 microK for the polarization of the cosmic background
radiation, assuming two years of observations. We discuss SPOrt scientific
goals in the light of WMAP results, in particular in connection with the
emerging double-reionization cosmological scenario.
