Global navigation satellite systems (GNSS) as well as their transmitted radio signal propagation features in space environment are described in this paper. The significant sources of the radio signal disturbances are atmosphere and its layers, particulary ionosphere, its main parameter - Total Electron Content, ionospheres scintillation, the Sun and its activity. These natures’ elements significantly affect the GNSS measurements and the accuracy of positioning. The paper gives an insight into the satellite "Solar Dynamics Observatory” (SDO) developed by NASA.