The experience gained from ROSA radio occultation instruments flying nowadays on three missions (OCEANSAT-2, SAC-D and MEGHATROPIQUE) is presented in this paper. Insights on different aspects of GNSS remote sensing like tropospheric sounding, ionospheric sounding are presented here, compared with state-of-the-art reference data (ECMWF, colocations). Further insight on ROSA instrument from in-flight data (clock stability, signal amplitude characterization) is provided as well.