Created By:Ravi Kant Singh | Created Date :27 April, 2023
The Global Positioning System (GPS), initially Navstar GPS is a radionavigation system based on satellites operated by the United States government and operated by the United States Space Force. It is among the worldwide GPS navigation systems (GNSS) which provides the information on time and geolocation to the GPS receiver located anywhere within or near the Earth in areas with an unobstructed line of view to at least four GPS satellites.
The GPS project was launched in the U.S. Department of Defense in 1973. The first prototype spacecraft launched in the year 1978 and the complete array of satellites was made operating in 1993. Initially, the spacecraft was only used for the United States military, civilian usage was permitted in the 1980s, following an executive order issued by the president Ronald Reagan after the Korean Air Lines Flight 007 crash.
The advancement of technology and the increasing demands on the system have been a catalyst for efforts to modernize GPS and to implement an advanced generation of GPS Block IIIA satellites as well as the Next Generation Operational Control System (OCX). that was approved through members of the U.S. Congress in 2000.
In the beginning of the 1990s, GPS positional accuracy was reduced in the hands of authorities of the United States government by a program known as Selective Availability, which could selectively reduce or stop accessibility to GPS at any moment such as was the case with those in the Indian forces in 1999 as part of the Kargil War. The program was halted on May 1st 2000, in line to a bill that was that was signed to law by president Bill Clinton. In the aftermath, a number of nations have either developed or are in the process creating different regional or global system of navigation by satellite.
The Chinese BeiDou Navigation Satellite System began worldwide services in the year 2018 and completed its full-scale deployment in 2020. Additionally, there's other systems like the European Union Galileo navigation satellite system, as well as India's NavIC. Japan's Quasi Zenith Satellite System (QZSS) is an GPS satellite-based enhancement system that aims to increase the accuracy of GPS in Asia and Oceania and beyond, with navigation by satellite independent of GPS set for 2023.
After the removal of selective availability during 2000 GPS could achieve a 5 meter (16 feet) accuracy. GPS receivers using L5 band technology L5 band have significantly higher precision, able to pinpoint within 30-centimeters (11.8 in) in accuracy, while users with higher end capabilities (typically the land and engineering systems) can have precision on a variety of band signals within 2 centimeters. Some even have sub-millimeter measurement accuracy in long-term tests.
Smartphones, which are consumer devices can be as precise as within 4.9 meters (or higher if assistive services such as Wi-Fi positioning that are also available). In May 2021, 16 GPS satellites were broadcasting L5 signals. These signals are deemed to be pre-operational and set to be broadcasting to 24 satellites by 2027.
Civil use was permitted in the 1980s. It was the work of Gladys West is credited as important in the creation of computer-based techniques to detect satellite positions with the accuracy required to be used in GPS.
The concept of GPS is based on similar radio-navigation systems based on the ground including LORAN or Decca Navigator. Decca Navigator, developed in the 1940s.
In 1955, Friedwardt Winterberg proposed a test of general relativity--detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. General relativity and special relativity predicted that clocks of GPS satellites as seen by people located on Earth are 38 microseconds more frequently than clocks on Earth. The structure of GPS is able to correct this disparity since, if it didn't, GPS calculated positions would have errors as large as 10 km per day (6 miles/day).
