The Worldwide Positioning System (GPS) is built on a global network of satellites that broadcast radio signals from a medium earth orbit to provide navigation services.
History of GPS
Global Positioning System (GPS), officially named NAVSTAR GPS, is a fully functional Global Navigation Satellite System (GNSS) developed by the United States Department of Defense and accessible as a public good to civilians. It enables a GPS receiver to determine its location, speed, direction of speed, and time, by making use of a constellation of at least 24 medium Earth orbit satellites, managed by the United States Air Force 50th Space Wing, that transmit precise microwave signals. Maintenance of the GPS costs about US$750 million per year.
How does GPS work?
Three components make up the GPS: the space segment (SS), the control segment (CS), and the user segment (US).
The orbiting GPS satellites, also known as Space Vehicles (SV), comprise the SS. There were 24 SVs included in the GPS design, with 4 SVs assigned to each of the six circular orbital planes, each possessing a 55 degree inclination tilt relative to the Earth’s equator, and 60 degrees right ascension of the ascending node separate them. Each SV orbits at an altitude of about 20,200 kilometers and at an orbital radius of 26,000 km twice every sidereal day.
Due to the specific arrangement of the orbits, at least six satellites are within line of sight from almost everywhere on the Earth’s surface at any given moment. Additional satellites have been added to provide redundant measurements and in effect, achieve better precision on GPS receiver calculations. There are now 31 SVs present in the SS as of September 2007.
The CS refers to the flight paths of the satellites. They are monitored by National Geospatial-Intelligence Agency (NGA) stations, as well as US Air Force stations in Colorado, Hawaii, Kwajalein, Ascension Island and Diego Garcia. The 2d Space Operations Squadron (2 SOPS) operates the master control station of the US Air Force Space Command, which is located at Schriever Air Force Base in Colorado Springs, Colorado. This station receives the tracking information from all other stations that are monitoring the flight paths.
Every GPS satellite is regularly contacted with a navigational update by 2 SOPS, created by a Kalman filter which uses various inputs such as those from ground monitoring stations and space weather information. The navigational updates are used to synchronize the atomic clocks on board the satellites to within one microsecond, and update the information about the satellites’ location and general system health, also known as almanac and ephemeris data, respectively.
What is the difference between GPS and GPS Receiver?
This is crucial to the system, because a GPS receiver is able to calculate its position by measuring the distance between itself and three or more GPS satellites, and then using trilateration. The receiver-to-satellite distance is measured by the time delay between transmission and reception of each GPS microwave signal.
The US refers to the GPS receiver of a user, which is composed of: a highly-stable clock, usually a crystal oscillator; an antenna, tuned to the frequencies transmitted by the satellites receiver-processors; and optionally a display for providing location and speed information to the user. Though originally only able to monitor four or five satellites simultaneously, a GPS receiver can now track anywhere between twelve and twenty of them.
The GPS is an important technology for both the military and civilians, making it a dual-use technology. It was originally developed for the military, where it aids in navigation, target tracking, missile and projectile guidance, reconnaissance and map-making, nuclear detonation detection, and search and rescue. For civilians, GPS provides an aid for navigation and land-surveying, and a means of calculating local velocity and orientation. It also serves as a time reference for several applications.
Interesting Facts About GPS
1. Do you know who was responsible for the invention of the GPS navigation system? Roger L. Easton of the Naval Research Laboratory, Bradford Parkinson of the Applied Physics Laboratory, and Ivan A. Getting of The Aerospace Corporation
2. With 31 operational satellites in orbit, the Global Positioning System (GPS) has become an integral component of every device we use, from mobile phones to automobiles.
3. Following a catastrophe, the GPS system was made available to the public. In 1983, Korean Airlines Flight 007 was shot down by the Soviet Union, killing all 269 passengers and crew members on board when the plane crossed Soviet territory, which was forbidden at the time. As a result of this event, President Ronald Reagan decided to open up the United States military satellite navigation system DNSS, which is now known as GPS, to the general public.
4. Navstar was the name given to GPS at the time of its inception. The first Navigation Satellite System (Navstar) satellite was launched in 1978. Only nine of the 10 satellites that were launched made it to their intended orbit. The first fully developed GPS satellite, launched in 1989, was the first of its kind.
5. The United States was the first country to utilize GPS for military reasons. The necessity for a worldwide navigation system during the Cold War prompted the development of the Global Positioning System (GPS).
6. There are a total of 31 satellites, including 2 backup satellites, circling the globe, with at least 24 GPS satellites in orbit around the planet. As a result, each GPS satellite completes one orbit around the globe every 12 hours.
Types of GPS
Did you know that GPS stands for Global Positioning System and is one of four Global Navigation Satellite Systems? The four global navigation satellite systems are: GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China) (China). Besides from that, there are two regional systems – the QZSS (Japan) and the IRNSS or NavIC (India).
GPS is an abbreviation for Global Positioning System (United States)
The Global Positioning System (GPS) is the most oldest GNSS system. It began operations in 1978 and was made accessible for usage across the world starting in 1994.
Its development was spurred by the necessity for a military navigation capability that could operate independently. And the United States military was the first to recognize this. As a result, the Transit system was established in 1964 specifically for this purpose. Transit, also known as NAVSAT, was a satellite that operated on the Doppler Effect and was used to give position information and navigation to missile submarines and surface ships, as well as hydrographic charting and geodetic surveying to the United States Army.
With the passage of time, the GPS system was made available to the general public. Current GPS satellite formations comprise 33 in total, with 31 of them in orbit and functioning at any one time. It is maintained by the United States Air Force, which is committed to ensuring the continued availability of at least 24 functioning GPS satellites. GPS has deployed a total of 72 satellites to far.
GLObal NAvigation Satellite System (often known as GLONASS) is a global navigation satellite system developed by Russia. GLONASS began operations in the year 1993 with 12 satellites in two orbits at a height of 19,130 kilometers. It was the first global navigation satellite system. Right now there are a total of 27 satellites in orbit, all of which are fully functioning. GLONASS is a satellite navigation system maintained by the Russian Aerospace Defense Forces and is the second alternative navigational system currently in use.
Galileo formed in the name of Galilei was a scientist who lived in the 16th century (EU)
Galileo is the global navigation satellite system (GNSS) of the European Union. It is being built by the European Space Agency, and it will be operated by the European GNSS Agency. For civilian and commercial purposes, Galileo is a worldwide navigation system that is currently in operation. The Galileo system will be comprised of 30 active satellites and six in-orbit spares when it is completely operational. Twenty-two of the thirty satellites are currently in orbit. Galileo began providing Early Operational Capability in 2016, and it is likely to achieved full operational capability in 2020, according to the European Space Agency.
BeiDou is a Chinese word that means “beautiful day” (China)
China’s BeiDou satellite navigation system is a global navigation system. It now has a total of 22 operational satellites in orbit, with the entire system expected to consist of 35 satellites when completed. BeiDou is comprised of two distinct groupings: BeiDou-1 and BeiDou-2. BeiDou-1, also known as the first generation, was a satellite system consisting of three satellites that was launched in 1989. As of the year 2000, it provided limited coverage and navigation services, with the majority of its customers being in China and surrounding areas of the world. Beidou-1 was deactivated at the end of 2012 after serving its purpose.
A version of the system called as BeiDou-2 (also known as COMPASS) is the second generation of the system. A partial constellation of ten satellites was launched into orbit in the year 2011, and it became operational in the following year. BeiDou-3 is the next iteration of this technology. In March 2015, the first BDS-3 satellite was successfully launched into orbit. As of January 2018, a total of nine BDS-3 satellites have been successfully launched. BeiDou-3 is likely to be completely operational by the end of 2020.
In Japan, the Quasi-Zenith Satellite System is a regional satellite navigation system that is currently under development by the Satellite Positioning Research and Application Center, which is still in the process of being built. According to current designs, the QZSS constellation will consist of seven satellites, of which four are currently in orbit. When completed, the QZSS will offer extremely accurate and reliable location services throughout the Asia-Oceania area. The system is scheduled to be fully operational by the end of 2018. QZSS is expected to be compatible with GPS.
IRNSS NAVIC (India)
The Indian Regional Navigation Satellite System (IRNSS), which was subsequently given the operational name of NavIC or NAVigation with Indian Constellation, is the country’s regional satellite navigation system. The Indian Space Research Organization (ISRO) launched and operates the Indian Regional Navigation Satellite System (IRNSS), which covers India and neighboring areas with a range of up to 1,500 kilometers. All seven satellites are in orbit, but the first satellite – IRNSS A – is now not operational since the Indian Space Research Organization (ISRO) stated that all three atomic clocks on board had broken at some point last year.
After an unusual event occurred in August 2017, ISRO’s attempt to launch a replacement satellite failed to successfully detach from the launch vehicle, resulting in the loss of the replacement satellite. At the moment, three IRNSS satellites are in geostationary orbit while the other four are in geosynchronous orbits, according to the organization. There is still some time before India would be able to take use of its services.
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