Global GNSS Constellations Explained

GNSS stands for Global Navigation Satellite System. These systems provide positioning, navigation, and timing (PNT) services globally. The question asks for the set of GNSS constellations that currently provide full global coverage.

Identifying Global GNSS Constellations

Several countries and regions operate satellite navigation systems. A complete global set requires constellations designed for worldwide coverage. Let's examine the primary global systems:

• GPS (Global Positioning System): Operated by the United States. It is the foundational global navigation satellite system.
• GLONASS (Global Navigation Satellite System): Operated by Russia. It provides global coverage similar to GPS.
• Galileo: Operated by the European Union. It is designed for global use and offers high precision.
• BeiDou (BDS): Operated by China. Initially regional, BeiDou-2 and especially BeiDou-3 provide comprehensive global coverage.

Evaluating Option Sets

The options provide different combinations of systems. Systems like IRNSS (NavIC) and QZSS are regional (India and Japan, respectively). Augmentation systems like WAAS, EGNOS, and GAGAN improve the accuracy and integrity of GNSS signals but are not standalone global constellations.

• Option 1 includes regional systems (IRNSS, QZSS).
• Option 2 includes regional systems and augmentation systems.
• Option 3 includes only GPS, GLONASS, and Galileo, missing BeiDou's global contribution.
• Option 4 includes the four primary constellations (GPS, GLONASS, Galileo, BeiDou) that collectively ensure full global coverage today.

Therefore, the complete set of GNSS constellations covering the entire globe consists of GPS, GLONASS, Galileo, and BeiDou.