I walk by an apartment complex parking lot and see this sign on the back window of a pickup. Apparently, Combat-Plane.system is a GPS tracking system for companies that have fleets of vehicles. According to Wikipedia, a GPS tracking unit or tracker is a navigation device normally on a vehicle, asset, person or animal that uses the Global Positioning System or GPS to determine its movement and location. Locations are stored in the tracking unit or transmitted to an Internet-connected device using the cellular network, radio or satellite modem embedded in the unit. Various companies buy position and track data for marketing. It is also used in the military and law enforcement to shut down and pick up repossession/thefts and find truck loads. In 2020 tracking was a $2 billion business. In the Gulf War 10% or more of the targets used trackers. Who knew?
My limited knowledge of GPS is in the car. I can remember when Garmin and TomTom devices first came out. It was like magic. I had been waiting for the day when my car would tell me which way to turn — no more getting lost, no more stopping to ask directions, no more trying to read unfolded maps while driving. GPS devices were certifiable miracles, the best thing since sliced bread or bagged salad. And what a treat to be able to select the accent of your speaker on the device. It was always a tossup between the male Brits and Aussies for me. The American women’s voices often seemed strident, accusatory: “Re-cal-cu-lating.” Of course, now we have apps on our phones for Google Maps and Waze, which makes it even more convenient and a lot cheaper. I love the technology, but am not sure how it works. Let’s find out.
The Global Positioning System or GPS, originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the relatively weak GPS signals.
GPS does not require the user to transmit any data, and it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. GPS provides critical positioning capabilities to military, civil and commercial users around the world. The United States government created the system, maintains it and makes it freely accessible to anyone with a GPS receiver.
The GPS project was started by the U.S. Department of Defense in 1973, with the first prototype spacecraft launched in 1978 and the full constellation of 24 satellites operational in 1993. Originally limited to use by the United States military, civilian use was allowed from the 1980s following an executive order from President Ronald Reagan. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System. Announcements from Vice President Al Gore and the Clinton Administration in 1998 initiated these changes, which were authorized by the U.S. Congress in 2000.
During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability;" this was discontinued on May 1, 2000 by a law signed by President Bill Clinton.
The GPS service is provided by the United States government, which can selectively deny access to the system — as happened to the Indian military in 1999 during the Kargil War — or degrade the service at any time. As a result, several countries have developed — or are in the process of setting up — other global or regional satellite navigation systems. The Russian Global Navigation Satellite System or GLONASS was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s. GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, to within 6.6 feet. China's BeiDou Navigation Satellite System began global services in 2018 and finished its full deployment in 2020. There are also the European Union Galileo positioning system and India's NavIC. Japan's Quasi-Zenith Satellite System is a GPS satellite-based augmentation system to enhance GPS's accuracy in Asia-Oceania, with satellite navigation independent of GPS scheduled for 2023.
When selective availability was lifted in 2000, GPS only had accuracy within about 16 feet. The latest stage of accuracy enhancement uses the L5 band and is now fully deployed. GPS receivers released in 2018 that use the L5 band can have much higher accuracy, pinpointing to within 11.8 inches.
History
The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors — including classified engineering design studies from the 1960s. The U.S. Department of Defense developed the system, which originally used 24 satellites. It was initially developed for use by the United States military and became fully operational in 1995. Civilian use was allowed from the 1980s. Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corp. and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it. The work of Dr. Gladys West is credited as instrumental in the development of computational techniques for detecting satellite positions with the precision needed for GPS.
The design of GPS is based partly on similar ground-based radio-navigation systems, such as LORAN — short for long range navigation — and the Decca Navigator, developed in the early 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. Special and general relativity predict that the clocks on the GPS satellites would be seen by the Earth's observers to run 38 microseconds faster per day than the clocks on the Earth. The GPS calculated positions would quickly drift into error, accumulating to 6 miles per day. This was corrected for in the design of GPS.
Predecessors
When the Soviet Union launched the first artificial satellite, Sputnik 1, in 1957, two American physicists — William Guier and George Weiffenbach — at Johns Hopkins University's Applied Physics Laboratory or APL decided to monitor its radio transmissions. Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit. The director of the APL gave them access to its UNIVAC electronic digital computer to do the heavy calculations required.
Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the user's location, given the satellite's. At the time, the Navy was developing the submarine-launched Polaris missile, which required them to know the submarine's location. This led them and APL to develop the TRANSIT system. In 1959, ARPA — renamed DARPA for Defense Advanced Research Projects Agency in 1972 — also played a role in TRANSIT.
TRANSIT was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour.
In 1967, the U.S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS.
In the 1970s, the ground-based OMEGA navigation system — based on phase comparison of signal transmission from pairs of stations — became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy.
Although there were wide needs for accurate navigation in military and civilian sectors, almost none of those was seen as justification for the billions of dollars it would cost in research, development, deployment and operation of a constellation of navigation satellites. During the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the U.S. Congress. This deterrent effect is why GPS was funded. It is also the reason for ultra-secrecy at that time. The nuclear triad consisted of the United States Navy's submarine-launched ballistic missiles or SLBMs, along with U.S. Air Force strategic bombers and intercontinental ballistic missiles. Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier.
Precise navigation would enable United States ballistic missile submarines to get an accurate fix of their positions before they launched their SLBMs. The USAF, with two thirds of the nuclear triad, also had requirements for a more accurate and reliable navigation system. The U.S. Navy and U.S. Air Force were developing their own technologies in parallel to solve what was essentially the same problem.
To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms — comparable to the Soviet SS-24 and SS-25 — and so the need to fix the launch position had similarity to the SLBM situation.
In 1960, the Air Force proposed a radio-navigation system called MOSAIC or MObile System for Accurate ICBM Control that was essentially a 3-D LORAN. A follow-on study, Project 57, was worked in 1963 and it was "in this study that the GPS concept was born." That same year, the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS" and promised increased accuracy for Air Force bombers as well as ICBMs.
Updates from the Navy TRANSIT system were too slow for the high speeds of Air Force operation. The Naval Research Laboratory continued making advances with their Timation or Time Navigation satellites, first launched in 1967, second launched in 1969, with the third in 1974 carrying the first atomic clock into orbit and the fourth launched in 1977.
Another important predecessor to GPS came from a different branch of the United States military. In 1964, the U.S. Army orbited its first Sequential Collation of Range or SECOR satellite used for geodetic surveying. The SECOR system included three ground-based transmitters at known locations that would send signals to the satellite transponder in orbit. A fourth ground-based station — at an undetermined position — could then use those signals to fix its location precisely. The last SECOR satellite was launched in 1969.
Development
During Labor Day weekend in 1973, a meeting of about twelve military officers at the Pentagon discussed the creation of a Defense Navigation Satellite System or DNSS. It was at this meeting that the real synthesis that became GPS was created. Later that year, the DNSS program was named Navstar. It is often erroneously considered an acronym for "NAVigation System Using Timing and Ranging" but was never considered as such by the GPS Joint Program Office. With the individual satellites being associated with the name Navstar — as with the predecessors TRANSIT and Timation — a more fully encompassing name was used to identify the constellation of Navstar satellites, Navstar-GPS. Ten "Block I" prototype satellites were launched between 1978 and 1985.
After Korean Air Lines Flight 007 — a Boeing 747 carrying 269 people — was shot down in 1983 after straying into the USSR's prohibited airspace in the vicinity of Sakhalin and Moneron Islands, President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good. The first Block II satellite was launched on February 14, 1989, and the 24th satellite was launched in 1994. The GPS program cost at this point — not including the cost of the user equipment but including the costs of the satellite launches — has been estimated at $5 billion in then-year dollars.
Initially, the highest-quality signal was reserved for military use, and the signal available for civilian use was intentionally degraded, in a policy known as Selective Availability. This changed with President Bill Clinton signing on May 1, 2000, a policy directive to turn off Selective Availability to provide the same accuracy to civilians that was afforded to the military. The directive was proposed by U.S. Secretary of Defense William Perry in view of the widespread growth of differential GPS services by private industry to improve civilian accuracy. Moreover, the U.S. military was actively developing technologies to deny GPS service to potential adversaries on a regional basis.
Since its deployment, the U.S. has implemented several improvements to the GPS service, including new signals for civil use and increased accuracy and integrity for all users, all the while maintaining compatibility with existing GPS equipment. Modernization of the satellite system has been an ongoing initiative by the U.S. Department of Defense through a series of satellite acquisitions to meet the growing needs of the military, civilians and the commercial market.
Structure – user segment
The user segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service and tens of millions of civil, commercial and scientific users of the Standard Positioning Service. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors and a highly stable clock, often a crystal oscillator. They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, as of 2007, receivers typically have between 12 and 20 channels. Though there are many receiver manufacturers, they almost all use one of the chipsets produced for this purpose.
Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol. Although this protocol is officially defined by the National Marine Electronics Association, references to this protocol have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws. Other proprietary protocols exist as well, such as the SiRF and MTK protocols. Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth.
Civilian applications
Atmosphere
Studying the troposphere delays (recovery of the water vapor content) and ionosphere delays (recovery of the number of free electrons). Recovery of Earth surface displacements due to the atmospheric pressure loading.
Astronomy
Both positional and clock synchronization data is used in astrometry and celestial mechanics and precise orbit determination. GPS is also used in both amateur astronomy with small telescopes, as well as by professional observatories, for finding extrasolar planets.
Automated vehicles
Applying location and routes for cars and trucks to function without a human driver.
Cartography
Both civilian and military cartographers use GPS extensively.
Cellular telephony
Clock synchronization enables time transfer, which is critical for synchronizing its spreading codes with other base stations to facilitate inter-cell handoff and support hybrid GPS/cellular position detection for mobile emergency calls and other applications. The first handsets with integrated GPS launched in the late 1990s. The U.S. Federal Communications Commission mandated the feature in either the handset or in the towers for use in triangulation in 2002, so emergency services could locate 911 callers. Third-party software developers later gained access to GPS application programming interfaces from Nextel upon launch, followed by Sprint in 2006 and Verizon soon thereafter.
Disaster relief/emergency services
Many emergency services depend upon GPS for location and timing capabilities.
GPS tours
Location determines what content to display; for instance, information about an approaching point of interest.
Recreation – location-based mobile games
Geocaching - an outdoor recreational activity, in which participants use a GPS receiver or mobile device and other navigational techniques to hide and seek containers — called "geocaches" or "caches" — at specific locations marked by coordinates all over the world.
Geodashing - an outdoor sport in which teams of players use GPS receivers to find and visit randomly selected "dashpoints" — also called "waypoints" — around the world and report what they find. The objective is to visit as many dashpoints as possible.
GPS drawing - also known as GPS Art, is a method of drawing where an artist uses a GPS device and follows a pre-planned route to create a large-scale picture or pattern. The .GPX data file recorded during the drawing process is then visualized, usually overlaying it as a line on a map of the area. Artists usually run or cycle the route — while cars, vans, boats and airplanes are utilized to create larger pieces.
Waymarking - the practice of marking paths in outdoor recreational areas with signs or markings that follow each other at certain distances and mark the direction of the trail.
Pokémon Go - a 2016 augmented reality mobile game developed and published by Niantic in collaboration with Nintendo and The Pokémon Company for iOS and Android devices. It uses mobile devices with GPS to locate, capture, train and battle virtual creatures, called Pokémon, which appear as if they are in the player's real-world location. The game is free-to-play; it uses a freemium business model combined with local advertising and supports in-app purchases for additional in-game items. The game launched with around 150 species of Pokémon, which had increased to around 600 by 2020.
Robotics
Self-navigating, autonomous robots using GPS sensors, which calculate latitude, longitude, time, speed and heading.
Tectonics
GPS enables direct fault motion measurement of earthquakes. Between earthquakes GPS can be used to measure crustal motion and deformation to estimate seismic strain buildup for creating seismic hazard maps.
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