Space qualified frequency sources (clocks) for current and future GNSS applications

Accurate and stable frequency reference sources are critical for commercial, navigation, military and scientific space applications. Several levels of frequency references are suitable for space applications. This paper discusses similarities and differences among single distributed oscillators for communications satellites, master oscillator groups for communications systems, and atomic clocks for military and navigation systems. This paper builds on reference [1] and broadly describes frequency sources on current and upcoming global navigation satellite systems (GNSS). The three current systems are the Global Navigation Satellite System (GLONASS), the Global Positioning System (GPS), and the Galileo system. The upcoming navigation systems are: China´s Compass satellite positioning system, Japan´s quasi-zenith satellite system (QZSS), India´s regional navigation satellite system (IRNSS), GPS-IIF, and GPS-III.