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Global Positioning System (GPS)

By Amigos IAS

Why is it in the news?

  • The Global Positioning System (GPS) stands as a transformative force in modern technology, reshaping navigation for civilians, the military, and various industries.
  • Its far-reaching impact extends from precise scientific applications to urban planning, offering a paradigm shift in our understanding of location and profoundly influencing our sense of place.

Background

  • The Global Positioning System (GPS) was initiated by the U.S. Department of Defence in 1973, and the first satellite was launched in 1978. The GPS satellite constellation comprises 24 satellites orbiting the Earth in six orbits. These satellites are strategically placed to ensure global coverage, with each satellite completing two orbits per day.
  • The GPS system consists of three main components: the space segment, control segment, and user segment.
  • Space Segment: This segment comprises the 24 satellites in orbit, ensuring that at least four satellites are visible from any point on Earth. The satellites continuously broadcast signals containing information about their location, operational status, and the time of signal emission.
  • Control Segment: The control segment involves a global network of ground-based control stations and antennae. These stations track the satellites, monitor their performance, and transmit commands to ensure the system’s accuracy and reliability. The master control station is located at Schriever Air Force Base in Colorado, with an alternate station at Vandenberg Air Force Base in California.
  • User Segment: This segment involves the use of GPS in various sectors and applications, including agriculture, construction, logistics, military operations, and more. The user segment encompasses the devices and applications that leverage GPS data for navigation and positioning.

 

How GPS Works

  • Satellite Signals: Each GPS satellite continuously broadcasts radio signals at specific frequencies, namely L1 (1,575.42 MHz) and L2 (1,227.6 MHz). These signals include information about the satellite’s location, operational status, and the time at which the signal is emitted.
  • Receiver Calculation: A GPS receiver, such as the one in your smartphone, picks up these signals. By calculating the precise distance from at least four satellites, the receiver can triangulate its position in four dimensions (three in space and one in time relative to the satellite clock).
  • Signal Travel Time: The distance is determined by the speed of light and the signal’s travel time. The signal’s travel time is the difference between the time on the receiver’s clock and the time at which the signal was emitted.
  • To ensure accuracy, adjustments are made for factors such as the weaker gravitational potential around the satellites, which causes their onboard clocks to run slightly faster than those on the ground. Both the general and special theories of relativity are considered in these adjustments.
  • To maintain accurate timekeeping, each satellite is equipped with an atomic clock. Atomic clocks exploit the resonant frequency of electrons around atoms to measure time precisely. The clocks on modern GPS satellites are synchronized to within 10 nanoseconds of each other and with ground reference clocks.
Global Navigation Satellite Systems (GNSS)

·       Other countries operate GNSS systems, including Australia, China, the European Union, India, Japan, South Korea, Russia, and the UK. These systems, such as GLONASS, Galileo, and BeiDou, are part of international cooperation efforts to ensure compatibility and mutual benefit.

India’s Navigation Systems

·       India’s own Navigation with Indian Constellation (NavIC) consists of seven satellites, utilizing rubidium atomic clocks and operating in multiple frequency bands. The system facilitates ground-based navigation.

·       India also operates the GPS-Aided Geo Augmented Navigation (GAGAN) system, developed by the Indian Space Research Organisation (ISRO) and the Airports Authority of India. GAGAN primarily serves safety-of-life civil aviation applications in Indian airspace.

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