What is GNSS?
Global Navigation Satellite Systems (GNSS) is the generic term for satellite-based positioning systems. GPS (Global Positioning System), operated by the US Space Force, is the original and most widely deployed system (24+ satellites at 20,200 km MEO). Europe's Galileo (30 satellites at 23,222 km), Russia's GLONASS (24 satellites at 19,100 km), and China's BeiDou (30+ satellites across multiple orbits) are fully operational alternatives. Modern GNSS receivers typically use signals from multiple constellations simultaneously, improving accuracy and availability.
How positioning works
GNSS satellites transmit precisely timed signals generated by onboard atomic clocks (caesium or rubidium, accurate to nanoseconds). A receiver measures the time it takes for signals from at least 4 satellites to arrive, and uses these pseudo-ranges to compute its 3D position via trilateration. The timing precision required is extraordinary: a 1 nanosecond error in signal timing translates to approximately 30 cm of position error.
Augmentation systems
Standard GNSS provides position accuracy of 3–5 metres. Satellite-Based Augmentation Systems (SBAS) — WAAS (USA), EGNOS (Europe), MSAS (Japan), GAGAN (India) — broadcast correction signals via GEO satellites that improve accuracy to 1–3 metres horizontally. Differential GPS (DGPS) and Real-Time Kinematic (RTK) systems using ground reference stations achieve centimetre-level accuracy for surveying, precision agriculture, and autonomous vehicle navigation.
Satellite industry applications
GNSS underpins satellite orbit determination (spacecraft carry GNSS receivers), attitude reference (GPS attitude determination systems), ground station coordination, and satellite-based timing synchronisation for telecommunications networks. The GNSS market generates over $100 billion annually in receiver and application revenue, far exceeding the value of the satellite infrastructure itself.