The Global Positioning System (GPS), one of the few technologies that have had a revolutionary impact on civilian, military, scientific, and urban realms, was initiated by the U.S. Department of Defense in 1973. Since its introduction, GPS has redefined our sense of location and significantly impacted diverse sectors worldwide.
The GPS primarily consists of three main segments; the Space segment, Control segment, and User segment.
The Space Segment of GPS
The Space segment of the GPS comprises 24 satellites in six orbits which are positioned 20,200 km above Earth. These satellites ensure global coverage by allowing receivers to access signals from at least four satellites simultaneously. This is especially fundamental for accurate positioning. Each orbit houses four satellites and each satellite completes two orbits in a single day.
The Control Segment of GPS
The Control segment of the GPS is managed by ground-based stations which ensure satellite performance and signal accuracy. This segment adheres to the Standard Positioning Service (SPS) standards published in 2020. Various key stations across the globe manage and monitor the GPS system’s integrity.
The User Segment of GPS
The User segment of GPS encompasses diverse sectors ranging from agriculture to military operations. As of 2021, there are an estimated 6.5 billion GNSS (Global Navigation Satellite System) devices worldwide. This number is expected to surge to 10 billion by 2031, underlining the pervasive influence of the GPS.
The Functionality and Precision of GPS
GPS operates through a complex process of satellite-transmitted radio signals at specific frequencies. These radio signals are received and triangulated by GPS receivers, enabling them to pinpoint a precise location in three dimensions of space and one of time. Satellites maintain accurate timekeeping for GPS using atomic clocks.
GNSS in Other Countries
Several countries operate their own Global Navigation Satellite Systems (GNSS) alongside the GPS. Such systems are currently run by countries including Australia, China, the European Union (EU), India, Japan, South Korea, Russia, and the U.K. Notably, Russia’s GLONASS, the EU’s Galileo, and China’s BeiDou systems all operate on a global scale.
India’s Tryst with GNSS: The NavIC System
In 2006, India introduced its own Indian Regional Navigation Satellite System, later rechristened Navigation with Indian Constellation (NavIC). This system consists of seven satellites, three of which are in geostationary orbits while the other four are in geosynchronous orbits. The NavIC satellites use rubidium atomic clocks and transmit data on specific frequency bands.
India also operates the GPS-Aided Geo Augmented Navigation (GAGAN) system, developed and established by the Indian Space Research Organisation (ISRO) and the Airports Authority of India. The primary purpose of GAGAN is for “safety-of-life civil aviation applications catering to the Indian airspace” and providing “correction and integrity messages for GPS”.
Civil Services Examination Questions on GPS and GNSS
Various questions on GPS and GNSS have previously appeared in the Civil Services Examinations. For instance, in 2023, the examination presented a question on which countries have their own Satellite Navigation System. The correct answer included Japan, among others. Another question in 2018 focused on aspects of the Indian Regional Navigation Satellite System (IRNSS), with the correct answer being that IRNSS has three satellites in geostationary and four satellites in geosynchronous orbits.
