The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth’s surface. GPS was originally developed by the United States Department of Defense to provide reliable navigation for military vehicles and personnel. However, GPS is now widely used by civilians for a variety of applications, including recreation, transportation, agricultural productivity, safety and security.
How GPS Works
GPS satellites circle the Earth twice a day in medium Earth orbit at an altitude of approximately 20,200 kilometers (12,550 miles). There are currently 31 operational GPS satellites in orbit, with more slated to be launched in the coming years. Each satellite transmits signal information back to Earth that includes precise timing data and orbital information. This data can be processed by a GPS receiver to calculate the exact location of the receiver on or near the Earth’s surface.
A minimum of four satellites must be visible from any given point on the planet’s surface in order for a GPS receiver to accurately determine its position. The positioning accuracy achievable with GPS depends on several factors, including satellite geometry (the relative positions of the visible satellites), signal blockage (by buildings or terrain), atmospheric conditions and other sources of error. In general though, civilian users can expect horizontal positioning accuracy within 3-5 meters under open sky conditions.
Applications of GPS
While originally designed for use by military forces, GPS has become an indispensable tool for civilians all over the world. Here are just some of the ways that people use GPS technology every day:
* Navigation: Car navigation systems make use of real-time traffic data and route guidance provided by GPS receivers to help drivers avoid congestion and reach their destination more quickly and efficiently. Similarly, portable handheld devices like smartphones and tablets utilize built-in GNSS receivers to provide turn-by-turn directions when walking or driving.
* Timing: Many critical infrastructure systems rely on accurate timekeeping for proper functioning – this includes everything from power grids to financial markets. By connecting to global timing signals broadcasted by GNSS satellites, these systems can stay properly synchronized even if their internal clocks drift slightly over time.
* Mapping: GIS software platforms make use of high-precision GNSS positioning data to create digital maps used in a variety industries such as surveying, land management and urban planning. This mapping data can also be used to track assets like vehicles or containers as they move around geographically over time.
GNSS constellation status as of June 2020:
Operational constellations:
BeiDou Navigation Satellite System (China) 18 operational + 2 under testing + 5 spares GLONASS (Russia) 24 operational + 2 under testing + 8 spares Galileo (EU/ESA) 22 operational + 12 under testing NavIC/IRNSS (India) 7 operational QZS/Michibiki (Japan) 4 operational+ 1 spare SBAS testbeds O3b Networks Medium Earth Orbit constellation(MEO)(global commercial service provider): 12 MEO FOC spacecraft , 6 additional MEO spacecraft planned Space Based Augmentation Systems WAAS/EGNOS/MSAS(US/Europe/Japan respectively): Geostationary Operational Environmental Satellites GOES – R series(US): 4 GEOGOES – R series spacecraft Starfire Optical Ground Station US Air Force research laboratory : 3 SFOG stations
In development / proposed constellations : Amazon Kuiper Belt Object Location Service(ABOLS)(commercial LEO constellation): 3200 LEO ABOLS spacecraft Apple low earth orbit satellite internet constellation(LEO)(commercial LEO constellation): 2000 LEO Apple spacecraft Blue Origin National Security Space LLC “Blue Moon”(proposed lunar lander ): 1 BMSN lunar lander SpaceX Starlink broadband internet system(LEO)(commercial LEOconstellation ): 42000 active LEPP Starlink User Terminals , 11792 NGSO Starlink V1L0P0 active sats , 2404 NGSO Starlink V1L0P1 active sats