Global satellite navigation systems is a research domain and technological concept focused on the design, implementation, and utilization of satellite constellations to provide autonomous geospatial positioning, navigation, and timing (PNT) services globally. This field investigates the principles governing satellite signal generation, transmission, and reception; orbital dynamics; error modeling and mitigation; and algorithmic approaches for precise PNT determination and integrity monitoring. Its significance lies in enabling ubiquitous and highly accurate PNT information essential for a wide array of scientific research, engineering applications, and critical infrastructure operations.