SPOrt (Sky Polarization Observatory) was a space experiment to be flown on the International Space Station during its Early Utilization Phase, aimed at measuring the microwave polarized emission with FWHM=7 degrees, in the frequency range 22-90 GHz. The galactic polarized emission can be observed at the lower frequencies and the polarization of the cosmic microwave background (CMB) at 90 GHz, where contaminants are expected to be less important. The extremely low level of the CMB Polarization signal (< 1 microK) calls for intrinsically stable radiometers. The SPOrt instrument was expressly devoted to CMB polarization measurements and the whole design was optimized for minimizing instrumental polarization effects.
The Sky Polarization Observatory is described in detail in The Sky Polarization Observatory, Cortiglioni, et.al., (New Astronomy, 9, 2004, 297-327), and Measuring CMB polarization from ISS: the SPOrt experiment, Colombo, L. P. L. ; SPOrt Collaboration. The project was canceled in 2005.