The PROGRA 2 instrument has been developed to constitute the largest possible database of polarimetric phase functions, to compare with laboratory measurements and remote sensing observations. 24 such phase curves and corresponding polarimetric parameters have presently been obtained. This paper will describe results on basaltic glass, volcanic black sand, and lunar soil simulant samples. A trend seems to be valid for all observed samples: the phase angle of maximum polarization is invariably lower when measured under microgravity conditions as compared to ground-based measurements.