Global Navigation Satellite System

What is GNSS?

GNSS is the international standard term for satellite-based navigation systems. While "GPS" is often used colloquially to refer to any satellite navigation, GPS is technically just one GNSS constellation — the American one. Four fully operational GNSS constellations exist: the United States' GPS (Global Positioning System, 31 satellites), Russia's GLONASS (Globalnaya Navigatsionnaya Sputnikovaya Sistema, 24 satellites), the European Union's Galileo (30 satellites), and China's BeiDou (35+ satellites). Each provides global or near-global coverage independently.

All four constellations work on the same fundamental principle: satellites in medium Earth orbit (approximately 20,000 km altitude) broadcast precise timing signals. A receiver on the ground or in an aircraft measures the time delay from multiple satellites and calculates its three-dimensional position through trilateration. A minimum of four satellites is needed for a 3D position fix — three for position and one to correct the receiver's clock error. Modern receivers track all four constellations simultaneously, giving them access to 120+ satellites and improving accuracy, availability, and integrity.

Aviation-grade GNSS receivers are augmented by systems like SBAS (Satellite-Based Augmentation Systems), which provide corrections and integrity monitoring. WAAS in North America, EGNOS in Europe, MSAS in Japan, and GAGAN in India all enhance GNSS performance for aviation use. These augmentation systems enable precision approach capabilities (LPV) that rival ILS in performance, using only satellite signals.

Why It Matters for Airspace Risk

All four GNSS constellations share a fundamental vulnerability: the signals arriving at Earth's surface are extremely weak — roughly equivalent to a 25-watt light bulb viewed from 20,000 kilometers. This makes them susceptible to both jamming (overwhelming the signal with noise) and spoofing (transmitting fake signals that mimic the real ones). A jammer with a few watts of power can deny GNSS reception across a wide area, and a sophisticated spoofer can cause receivers to compute wildly incorrect positions without triggering any alarms.

The eastern Mediterranean, Middle East, and Baltic regions have experienced persistent GNSS interference since 2023, affecting all four constellations. While multi-constellation receivers are more resilient than single-constellation ones, a localized jammer affects GPS, Galileo, GLONASS, and BeiDou equally because they all use similar signal frequencies and power levels. For aviation risk assessment, GNSS interference tracking is now a core data input. FlySafe monitors reported interference events, NOTAM advisories, and crowd-sourced pilot reports to map the evolving geography of GNSS degradation worldwide.

Key Facts

• •Four operational GNSS constellations exist: GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China), totaling 120+ satellites.
• •GNSS signals are extremely weak at the surface (~-160 dBW), making all four constellations vulnerable to interference.
• •SBAS augmentation systems (WAAS, EGNOS, MSAS, GAGAN) enhance GNSS for aviation precision approaches.
• •Multi-constellation receivers improve availability but do not protect against local jamming, which affects all constellations simultaneously.
• •ICAO is developing standards for GNSS vulnerability mitigation, including Advanced RAIM (ARAIM) and alternative positioning systems.

Related Terms