Global Navigation Satellite system (GNSS) facilitate Earth based mapping via orbiting Satellite network. GNSS receivers calculate distance to these Satellites allowing users to Precisely determine their location. GNSS encompass multiple constellations providing global coverage. In order for GNSS systems to operate nowadays, high-precision atomic clock data must be transmitted from satellites to receivers, which requires massive bandwidth. The notion that each satellite transmits its own time information for this data redundancy. Current GNSSs rely on ground networks to monitor and correct satellite clocks. This project work discusses about how optical clocks are becoming more accurate timepieces than atomic clocks for wireless transmitter applications. An introduction to optical clock technology, including its history and features, is given at the beginning of the text. The Allan Deviation (ADEV) method is then used to evaluate clock stability, and a stability analysis is performed by comparing optical clocks with the current Global Navigation Satellite System (GNSS) satellite clocks. The results indicate that on board GNSS satellites, optical clocks are more stable than atomic clocks. To achieve spacecraft payload requirements, additional technological developments might be required. Optical clocks, as opposed to the current atomic clocks on board GNSS satellites, may provide sub-millimeter range inaccuracy and far better timing performance in the GNSS location. The Study Specifically Pinpoints the atomic of the Galileo satellites.