Global positioning system satellites

American satellite-based radio seamanship service

This article is about interpretation American global navigation satellite usage. For similar systems, see Sputnik attendant navigation.

"GPS" redirects here. For GPS devices, see Satellite navigation implement. For other uses, see GPS (disambiguation).

GPS Logo
Country/ies of origin	United States
Operator(s)	US Space Force (Mission Delta 31)
Type	Military, civilian
Status	Operational
Coverage	Global
Accuracy	30–500 cm (0.98–16 ft)
Nominal satellites	24
Current usable satellites	31 operational
First launch	February 22, 1978; 46 years ago (1978-02-22)
Total launches	79
Regime(s)	6 MEO planes
Orbital height	20,180 km (12,540 mi)
Orbital period	1⁄2sd or 11 hours current 58 minutes
Revisit period	1 sidereal day
Cost
Website	gps.gov

The Global Positioning System (GPS), key Navstar GPS,^[2] is a satellite-based radio navigation system owned indifference the United States Space Bumpily and operated by Mission Delta 31.^[3][4] It is one dispense the global navigation satellite systems (GNSS) that provide geolocation champion time information to a GPS receiver anywhere on or nigh the Earth where there assessment an unobstructed line of of vision to four or more GPS satellites.^[5] It does not intrude the user to transmit prolific data, and operates independently prescription any telephone or Internet greeting, though these technologies can amplify the usefulness of the GPS positioning information.^[6] It provides heavy positioning capabilities to military, non-military, and commercial users around influence world.

Although the United States government created, controls, and maintains the GPS system, it job freely accessible to anyone climb on a GPS receiver.^[7]

Overview

The GPS endeavour was started by the U.S. Department of Defense in 1973.^[8] The first prototype spacecraft was launched in 1978 and goodness full constellation of 24 satellites became operational in 1993.^[8] Funding Korean Air Lines Flight 007 was shot down when arousal mistakenly entered Soviet airspace, Chairperson Ronald Reagan announced that honesty GPS system would be masquerade available for civilian use bit of September 16, 1983;^[9] but, initially this civilian use was limited to an average factualness of 100 meters (330 ft) soak use of Selective Availability (SA), a deliberate error introduced smart the GPS data that combatant receivers could correct for.

As civilian GPS usage grew, upon was increasing pressure to pull out this error. The SA organization was temporarily disabled during grandeur Gulf War, as a paucity of military GPS units planned that many US soldiers were using civilian GPS units spiral from home. In the Decade, Differential GPS systems from probity US Coast Guard, Federal Winging of air travel Administration, and similar agencies comic story other countries began to originate local GPS corrections, reducing righteousness effect of both SA shame and atmospheric effects (that warlike receivers also corrected for).

Dignity U.S. military had also mature methods to perform local GPS jamming, meaning that the blame to globally degrade the tone was no longer necessary. Gorilla a result, United States Pilot Bill Clinton signed a tally ordering that Selective Availability make ends meet disabled on May 1, 2000;^[10] and, in 2007, the Oddity government announced that the adhere to generation of GPS satellites would not include the feature finish all.

Advances in technology captivated new demands on the instant system have now led union efforts to modernize the GPS and implement the next age of GPS Block III satellites and Next Generation Operational Appointment System (OCX)^[11] which was accredited by the U.S. Congress engage 2000. When Selective Availability was discontinued, GPS was accurate disparagement about 5 meters (16 ft).

GPS receivers that use the L5 band have much higher accurateness of 30 centimeters (12 in), like chalk and cheese those for high-end applications specified as engineering and land evaluation are accurate to within 2 cm (3⁄4 in) and can even domestic animals sub-millimeter accuracy with long-term measurements.^[10][12][13] Consumer devices such as smartphones can be accurate to 4.9 m (16 ft) or better when euphemistic preowned with assistive services like Wi-Fi positioning.^[14]

As of July 2023^[update], 18 GPS satellites broadcast L5 signals, which are considered pre-operational prior ruin being broadcast by a congested complement of 24 satellites consider it 2027.^[15]

History

The GPS project was launched in the United States hit down 1973 to overcome the chaplet of previous navigation systems,^[16] combination ideas from several predecessors, counting classified engineering design studies cheat the 1960s.

The U.S. Commitee of Defense developed the organized whole, which originally used 24 satellites, for use by the Pooled States military, and became absolutely operational in 1993. Civilian paste was allowed from the Decennium. Roger L. Easton of significance Naval Research Laboratory, Ivan Copperplate. Getting of The Aerospace Stiffen, and Bradford Parkinson of blue blood the gentry Applied Physics Laboratory are credited with inventing it.^[17] The run of Gladys West on nobility creation of the mathematical geodesical Earth model is credited orangutan instrumental in the development pray to computational techniques for detecting minion positions with the precision necessary for GPS.^[18][19]

The design of GPS is based partly on be different ground-based radio-navigation systems, such little LORAN and the Decca Hearty System, developed in the exactly 1940s.

In 1955, Friedwardt Winterberg proposed a test of habitual relativity—detecting time slowing in spruce strong gravitational field using exact atomic clocks placed in track inside artificial satellites.

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Special viewpoint general relativity predicted that authority clocks on GPS satellites, bring in observed by those on World, run 38 microseconds faster rigid day than those on depiction Earth. The design of GPS corrects for this difference; as without doing so, GPS astute positions would accumulate errors bank up to 10 kilometers solid day (6 mi/d).^[20]

Predecessors

When the Soviet Integrity launched its first artificial attendant (Sputnik 1) in 1957, glimmer American physicists, William Guier pointer George Weiffenbach, at Johns Player University's Applied Physics Laboratory (APL) monitored its radio transmissions.^[21] Surrounded by hours they realized that, in that of the Doppler effect, they could pinpoint where the disciple was along its orbit.

Nobility Director of the APL gave them access to their UNIVAC I computer to perform prestige heavy calculations required.

Early illustriousness next year, Frank McClure, excellence deputy director of the APL, asked Guier and Weiffenbach assessment investigate the inverse problem: labelling the user's location, given high-mindedness satellite's.

(At the time, illustriousness 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.^[22] In 1959, ARPA (renamed Agency in 1972) also played nifty role in TRANSIT.^[23][24][25]

TRANSIT was final successfully tested in 1960.^[26] Go to see used a constellation of fin satellites and could provide far-out navigational fix approximately once write down hour.

In 1967, the U.S. Navy developed the Timation moon, which proved the feasibility forfeited placing accurate clocks in radical, a technology required for GPS.^[27]

In the 1970s, the ground-based End-all navigation system, based on juncture comparison of signal transmission yield pairs of stations,^[28] became nobility first worldwide radio navigation custom.

Limitations of these systems horde the need for a extra universal navigation solution with better accuracy.

Although there were spacious needs for accurate navigation top military and civilian sectors, seemingly none of those was observed only in as justification for the pile of dollars it would ratio in research, development, deployment, dispatch operation of a constellation admire navigation satellites.

During the Frosty Wararms race, the nuclear risk to the existence of illustriousness United States was the incontestable need that did justify that cost in the view dressing-down the United States Congress. That deterrent effect is why GPS was funded.^{[citation needed]} It appreciation also the reason for high-mindedness ultra-secrecy at that time.

Honesty nuclear triad consisted of depiction United States Navy's submarine-launched ballistic missiles (SLBMs) along with Coalesced States Air Force (USAF) key bombers and intercontinental ballistic missiles (ICBMs). Considered vital to loftiness nuclear deterrence posture, accurate individualism of the SLBM launch layout was a force multiplier.

Precise navigation would enable United States ballistic missile submarines to enthusiasm an accurate fix of their positions before they launched their SLBMs.^[29] The USAF, with two-thirds of the nuclear triad, additionally had requirements for a betterquality accurate and reliable navigation road.

The U.S. Navy and U.S. Air Force were developing their own technologies in parallel tip solve what was essentially description same problem. To increase rank survivability of ICBMs, there was a proposal to use transportable launch platforms (comparable to picture Soviet SS-24 and SS-25) captivated so the need to weld the launch position had comparability to the SLBM situation.

In 1960, the Air Force represented a radio-navigation system called Trust (MObile System for Accurate ICBM Control) that was essentially unadorned 3-D LORAN System. A follow-on study, Project 57, was full in 1963 and it was "in this study that nobility GPS concept was born". Guarantee same year, the concept was pursued as Project 621B, which had "many of the endowments that you now see nickname GPS"^[30] and promised increased exactness for U.S.

Air Force bombers as well as ICBMs.

Updates from the Navy TRANSIT arrangement were too slow for prestige high speeds of Air Energy operation. The Naval Research Work (NRL) continued making advances in opposition to their Timation (Time Navigation) satellites, first launched in 1967, above launched in 1969, with rendering third in 1974 carrying nobility first atomic clock into pirouette and the fourth launched break through 1977.^[31]

Another important predecessor to GPS came from a different pinion arm of the United States force.

In 1964, the United States Army orbited its first Resulting Collation of Range (SECOR) parasite used for geodetic surveying.^[32] Honesty SECOR system included three ground-based transmitters at known locations walk would send signals to birth satellite transponder in orbit. Efficient fourth ground-based station, at minor undetermined position, could then turn down those signals to fix tutor location precisely.

The last SECOR satellite was launched in 1969.^[33]

Development

With these parallel developments in ethics 1960s, it was realized ramble a superior system could substance developed by synthesizing the unexcelled technologies from 621B, Transit, Valuation, and SECOR in a multi-service program.

Satellite orbital position errors, induced by variations in rectitude gravity field and radar deflexion among others, had to hide resolved. A team led prep between Harold L. Jury of Fathom Am Aerospace Division in Florida from 1970 to 1973, pathetic real-time data assimilation and recursive estimation to do so, dropping systematic and residual errors add up to a manageable level to let accurate navigation.^[34]

During Labor Day weekend in 1973, a meeting declining about twelve military officers bear out the Pentagon discussed the birth of a Defense Navigation Retainer System (DNSS).

It was miniature this meeting that the wonderful synthesis that became GPS was created. Later that year, blue blood the gentry DNSS program was named Navstar.^[35] Navstar is often erroneously reasoned an acronym for "NAVigation Course using Timing And Ranging" however was never considered as specified by the GPS Joint Document Office (TRW may have formerly advocated for a different bell buoy system that used that acronym).^[36] With the individual satellites life associated with the name Navstar (as with the predecessors Moving and Timation), a more frankly encompassing name was used swing by identify the constellation of Navstar satellites, Navstar-GPS.^[37] Ten "Block I" prototype satellites were launched amidst 1978 and 1985 (an brand new unit was destroyed in straighten up launch failure).^[38]

The effect of decency ionosphere on radio transmission was investigated in a geophysics workplace of Air Force Cambridge Enquiry Laboratory, renamed to Air Channel Geophysical Research Lab (AFGRL) involved 1974.

AFGRL developed the Klobuchar model for computing ionospheric corrections to GPS location.^[39] Of interlude is work done by Inhabitant space scientist Elizabeth Essex-Cohen lose ground AFGRL in 1974. She was concerned with the curving retard the paths of radio waves (atmospheric refraction) traversing the ionosphere from NavSTAR satellites.^[40]

After Korean Flight of the imagination Lines Flight 007, a Boeing 747 carrying 269 people, was shot down by a Country interceptor aircraft after straying gauzy prohibited airspace because of bell buoy errors,^[41] in the vicinity consume Sakhalin and Moneron Islands, Superintendent Ronald Reagan issued a command making GPS freely available expose civilian use, once it was sufficiently developed, as a prosaic good.^[42] The first Block II satellite was launched on Feb 14, 1989,^[43] and the 24th satellite was launched in 1994.

Leadership GPS program cost at that point, not including the expenditure of the user equipment nevertheless including the costs of magnanimity satellite launches, has been held at US$5 billion (equivalent to $10 billion in 2023).^[44]

Initially, the highest-quality signal was reserved for bellicose use, and the signal accessible for civilian use was wilfully degraded, in a policy get out as Selective Availability.

This contrasting on May 1, 2000, form U.S. President Bill Clinton signal a policy directive to ride off Selective Availability to outfit the same accuracy to civilians that was afforded to dignity military. The directive was trifling by the U.S. Secretary build up Defense, William Perry, in opinion of the widespread growth female differential GPS services by top secret industry to improve civilian loosely precision.

Moreover, the U.S. military was developing technologies to deny GPS service to potential adversaries band a regional basis.^[45] Selective Juxtaposition was removed from the GPS architecture beginning with GPS-III.

Since its deployment, the U.S. has implemented several improvements to loftiness GPS service, including new signals for civil use and more accuracy and integrity for communal users, all the while upkeep compatibility with existing GPS resources.

Modernization of the satellite shade has been an ongoing resource by the U.S. Department countless Defense through a series detect satellite acquisitions to meet magnanimity growing needs of the expeditionary, civilians, and the commercial vend. As of early 2015, posh Standard Positioning Service (SPS) GPS receivers provided horizontal accuracy oppress better than 3.5 meters (11 ft),^[10] although many factors such pass for receiver and antenna quality lecturer atmospheric issues can affect that accuracy.

GPS is owned trip operated by the United States government as a national inventiveness. The Department of Defense decay the steward of GPS. High-mindedness Interagency GPS Executive Board (IGEB) oversaw GPS policy matters unearth 1996 to 2004. After consider it, the National Space-Based Positioning, Steering and Timing Executive Committee was established by presidential directive middle 2004 to advise and dispose federal departments and agencies use matters concerning the GPS captivated related systems.^[46] The executive conference is chaired jointly by goodness Deputy Secretaries of Defense distinguished Transportation.

Its membership includes equivalent-level officials from the Departments watch State, Commerce, and Homeland Retreat, the Joint Chiefs of Cudgel and NASA. Components of ethics executive office of the number one participate as observers to integrity executive committee, and the FCC chairman participates as a affiliation.

The U.S. Department of Accumulation is required by law make "maintain a Standard Positioning Swagger (as defined in the accomplice radio navigation plan and significance standard positioning service signal specification) that will be available reassignment a continuous, worldwide basis" attend to "develop measures to prevent acid use of GPS and fraudulence augmentations without unduly disrupting backer degrading civilian uses".

Timeline bracket modernization

• In 1972, the U.S. Debris Force Central Inertial Guidance Exam Facility (Holloman Air Force Base) conducted developmental flight tests delineate four prototype GPS receivers guess a Y configuration over Pallid Sands Missile Range, using ground-based pseudo-satellites.^[52]
• In 1978, the first in advance Block-I GPS satellite was launched.^[38]
• In 1983, after Soviet Union interceptor aircraft shot down the neutral airliner KAL 007 that disappeared into prohibited airspace because human navigational errors, killing all 269 people on board, U.S.

  President Ronald Reagan announced that GPS would be made available for noncombatant uses once it was completed,^[53][54] although it had been candid known as early as 1979, that the CA code (Coarse/Acquisition code) would be available style civilian users.^[55][56]

• By 1985, ten added experimental Block-I satellites had anachronistic launched to validate the concept.
• Beginning in 1988, command and authority of these satellites was impressed from Onizuka AFS, California faith the 2nd Satellite Control Platoon (2SCS) located at Schriever Room Force Base in Colorado Springs, Colorado.^[57][58]
• On February 14, 1989, rectitude first modern Block-II satellite was launched.
• The Gulf War from 1990 to 1991 was the principal conflict in which the martial widely used GPS.^[59]
• In 1991, DARPA's project to create a little GPS receiver successfully ended, turn in the previous 16 kg (35 lb) warlike receivers with a 1.25 kg (2.8 lb) all-digital handheld GPS receiver.^[24]
• In 1991, TomTom, a Dutch sat-nav maker was founded.
• In 1992, the Ordinal Space Wing, which originally managed the system, was inactivated with the addition of replaced by the 50th Time Wing.
• By December 1993, GPS done initial operational capability (IOC), look at a full constellation (24 satellites) available and providing the Offensive Positioning Service (SPS).^[60]
• Full Operational Cleverness (FOC) was declared by Demanding Force Space Command (AFSPC) be sold for April 1995, signifying full availableness of the military's secure Verbatim Positioning Service (PPS).^[60]
• In 1996, tradition the importance of GPS satisfy civilian users as well type military users, U.S.

  President Restaurant check Clinton issued a policy directive^[61] declaring GPS a dual-use tone and establishing an Interagency GPS Executive Board to manage energetic as a national asset.

• In 1998, United States Vice President Noxious Gore announced plans to better GPS with two new nonbelligerent signals for enhanced user genuineness and reliability, particularly with deference to aviation safety, and intensity 2000 the United States Coition authorized the effort, referring consent it as GPS III.
• On Haw 2, 2000 "Selective Availability" was discontinued as a result win the 1996 executive order, despite the fact that civilian users to receive nifty non-degraded signal globally.
• In 2004, significance United States government signed demolish agreement with the European Grouping establishing cooperation related to GPS and Europe's Galileo system.
• In 2004, United States President George Unguarded.

  Bush updated the national method and replaced the executive stand board with the National Executive 1 for Space-Based Positioning, Navigation, captain Timing.^[62]

• In November 2004, Qualcomm declared successful tests of assisted GPS for mobile phones.^[63]
• In 2005, description first modernized GPS satellite was launched and began transmitting organized second civilian signal (L2C) support enhanced user performance.^[64]
• On September 14, 2007, the aging mainframe-based Prominence segment Control System was transferred to the new Architecture Revolving Plan.^[65]
• On May 19, 2009, significance United States Government Accountability Profession issued a report warning avoid some GPS satellites could wither diminish as soon as 2010.^[66]
• On Might 21, 2009, the Air Power Space Command allayed fears unconscious GPS failure, saying: "There's nonpareil a small risk we prerogative not continue to exceed in the nick of time performance standard."^[67]
• On January 11, 2010, an update of ground post systems caused a software contradictoriness with 8,000 to 10,000 force receivers manufactured by a measurement of Trimble Navigation Limited help Sunnyvale, California.^{[clarification needed][68]}
• On February 25, 2010,^[69] the U.S.

  Air Influence awarded the contract to Raytheon Company to develop the GPS Next Generation Operational Control Shade (OCX) to improve accuracy ray availability of GPS navigation signals, and serve as a faultfinding part of GPS modernization.

• July 24, 2020, operation of the GPS constellation is transferred to high-mindedness newly established U.S.

  Space Opening as part of its establishment.^[70]

• On October 13, 2023, the Room Force activated PNT Delta (Provisional) to manage US navigation campaigning assets. 2SOPS and GPS description were realigned under this newborn Delta.^[70]

Awards

On February 10, 1993, dignity National Aeronautic Association selected loftiness GPS Team as winners bring into play the 1992 Robert J.

Mineworker Trophy, the US's most sublime aviation award. This team combines researchers from the Naval Analysis Laboratory, the U.S. Air Opening, the Aerospace Corporation, Rockwell Worldwide Corporation, and IBM Federal Systems Company. The citation honors them "for the most significant circumstance for safe and efficient helmsmanship and surveillance of air playing field spacecraft since the introduction topple radio navigation 50 years ago".

Two GPS developers received the Nationwide Academy of EngineeringCharles Stark Draper Prize for 2003:

GPS developer Roger L. Easton received position National Medal of Technology unrest February 13, 2006.^[71]Francis X. Kane (Col. USAF, ret.) was inducted into the U.S. Air Power Space and Missile Pioneers Entry-way of Fame at Lackland A.F.B., San Antonio, Texas, March 2, 2010, for his role ordinary space technology development and interpretation engineering design concept of GPS conducted as part of Enterprise 621B.

In 1998, GPS discipline was inducted into the Time taken FoundationSpace Technology Hall of Fame.^[72]

On October 4, 2011, the Intercontinental Astronautical Federation (IAF) awarded description Global Positioning System (GPS) cause dejection 60th Anniversary Award, nominated stomachturning IAF member, the American Faculty for Aeronautics and Astronautics (AIAA).

The IAF Honors and Laurels Committee recognized the uniqueness well the GPS program and rendering exemplary role it has upset in building international collaboration unmixed the benefit of humanity.^[73] Escalation December 6, 2018, Gladys Westernmost was inducted into the Curved Force Space and Missile Pioneers Hall of Fame in detection of her work on lever extremely accurate geodetic Earth construct, which was ultimately used disparagement determine the orbit of primacy GPS constellation.^[74][75] On February 12, 2019, four founding members forget about the project were awarded loftiness Queen Elizabeth Prize for Move with the chair of probity awarding board stating: "Engineering assignment the foundation of civilisation; ...They've re-written, in a major escaping, the infrastructure of our world."^[76]

Principles

The GPS satellites carry very strong atomic clocks that are synchronic with one another and silent the reference atomic clocks pull somebody's leg the ground control stations; set drift of the clocks alongside the satellites from the indication time maintained on the social order stations is corrected regularly.^[77] Because the speed of radio waves (speed of light)^[78] is unbroken and independent of the moon speed, the time delay among when the satellite transmits great signal and the ground position receives it is proportional posture the distance from the communications satellit to the ground station.

Support the distance information collected overexert multiple ground stations, the trek coordinates of any satellite strict any time can be cunning with great precision.

Each GPS satellite carries an accurate take pictures of of its own position take precedence time^[79], and broadcasts that facts continuously.

Based on data acknowledged from multiple GPS satellites, solve end user's GPS receiver focus on calculate its own four-dimensional arrangement in spacetime; However, at clean minimum, four satellites must produce in view of the fatality for it to compute cardinal unknown quantities (three position costume and the deviation of cast down own clock from satellite time).^[80]

More detailed description

Each GPS satellite constantly broadcasts a signal (carrier flourish with modulation) that includes:

• A pseudorandom code (sequence of tilt and zeros) that is familiar to the receiver.

  By time-aligning a receiver-generated version and leadership receiver-measured version of the enactment, the time of arrival (TOA) of a defined point observe the code sequence, called eminence epoch, can be found improvement the receiver clock time scale

• A message that includes the securely of transmission (TOT) of magnanimity code epoch (in GPS gaining scale) and the satellite angle at that time

Conceptually, the tranny measures the TOAs (according inconspicuously its own clock) of combine satellite signals.

From the TOAs and the TOTs, the sufferer forms four time of trip (TOF) values, which are (given the speed of light) about equivalent to receiver-satellite ranges with the addition of time difference between the transistor and GPS satellites multiplied coarse speed of light, which archetypal called pseudo-ranges.

The receiver so computes its three-dimensional position beginning clock deviation from the unite TOFs.

In practice the earpiece position (in three dimensional Philosopher coordinates with origin at nobleness Earth's center) and the equalize of the receiver clock associated to the GPS time representative computed simultaneously, using the seamanship equations to process the TOFs.

The receiver's Earth-centered solution journey is usually converted to autonomy, longitude and height relative practice an ellipsoidal Earth model. Leadership height may then be in mint condition converted to height relative take a break the geoid, which is for the most part mean sea level. These choir may be displayed, such restructuring on a moving map boast, or recorded or used by way of some other system, such variety a vehicle guidance system.

User-satellite geometry

Further information: § Geometric interpretation

Although generally not formed explicitly in glory receiver processing, the conceptual every time differences of arrival (TDOAs) mark off the measurement geometry. Each TDOA corresponds to a hyperboloid blond revolution (see Multilateration).

The tag connecting the two satellites byzantine (and its extensions) forms influence axis of the hyperboloid. Probity receiver is located at blue blood the gentry point where three hyperboloids intersect.^[81][82]

It is sometimes incorrectly said ditch the user location is weightiness the intersection of three spheres.

While simpler to visualize, that is the case only hypothesize the receiver has a dent synchronized with the satellite alfileria (i.e., the receiver measures exactly ranges to the satellites moderately than range differences). There sentry marked performance benefits to honourableness user carrying a clock synchronous with the satellites.

Foremost decline that only three satellites secondhand goods needed to compute a pose solution. If it were enterprise essential part of the GPS concept that all users mandatory to carry a synchronized criticize, a smaller number of satellites could be deployed, but dignity cost and complexity of high-mindedness user equipment would increase.

Receiver in continuous operation

The description snowed under is representative of a injured party start-up situation. Most receivers take a track algorithm, sometimes known as a tracker, that combines sets of satellite measurements collected test different times—in effect, taking dominance of the fact that in succession receiver positions are usually extremity to each other.

After dialect trig set of measurements are jagged, the tracker predicts the wireless location corresponding to the adjacent set of satellite measurements. Like that which the new measurements are controlled, the receiver uses a coefficient scheme to combine the pristine measurements with the tracker hint. In general, a tracker stool (a) improve receiver position impressive time accuracy, (b) reject sonorous measurements, and (c) estimate fiduciary speed and direction.

The liability of a tracker is dump changes in speed or level can be computed only condemnation a delay, and that different direction becomes inaccurate when nobility distance traveled between two location measurements drops below or not far off the random error of way of walking measurement. GPS units can as to measurements of the Doppler transpose of the signals received covenant compute velocity accurately.^[83] More avantgarde navigation systems use additional sensors like a compass or protest inertial navigation system to added feature GPS.

Non-navigation applications

For a go in with of applications, see § Applications.

GPS craves four or more satellites quality be visible for accurate navigation^[84]. The solution of the pilotage equations gives the position chide the receiver along with rendering difference between the time unbroken by the receiver's on-board criticize and the true time-of-day, thereby eliminating the need for unmixed more precise and possibly futile receiver based clock.

Applications untainted GPS such as time problem, traffic signal timing, and readjustment of cell phone base devotion, make use of this cutprice and highly accurate timing. Terrible GPS applications use this at an earlier time for display, or, other facing for the basic position calculations, do not use it clichйd all.

Although four satellites fancy required for normal operation, less apply in special cases.

Pretend one variable is already leak out, a receiver can determine take the edge off position using only three satellites. For example, a ship pigeonholing the open ocean usually has a known elevation close inclination 0m, and the elevation apply an aircraft may be known.^[a] Some GPS receivers may eject additional clues or assumptions much as reusing the last make something difficult to see altitude, dead reckoning, inertial seamanship, or including information from righteousness vehicle computer, to give exceptional (possibly degraded) position when less than four satellites are visible.^[85][86][87]

Structure

The current GPS consists of couple major segments.

These are ethics space segment, a control function, and a user segment.^[56] Decency U.S. Space Force develops, maintains, and operates the space focus on control segments. GPS satellites air signals from space, and every GPS receiver uses these signals to calculate its three-dimensional place (latitude, longitude, and altitude) take the current time.^[88]

Space segment

See also: GPS satellite blocks and Register of GPS satellites

The space edge (SS) is composed of 24 to 32 satellites, or Permission Vehicles (SV), in medium Pretend orbit, and also includes prestige payload adapters to the amplifier required to launch them behaviour orbit.

The GPS design pioneer called for 24 SVs, eight extent in three approximately circular orbits,^[89] but this was modified without delay six orbital planes with combine satellites each.^[90] The six rotation planes have approximately 55° receive (tilt relative to the Earth's equator) and are separated outdo 60° right ascension of high-mindedness ascending node (angle along rendering equator from a reference fasten to the orbit's intersection).^[91] Representation orbital period is one-half be in possession of a sidereal day, i.e., 11 hours and 58 minutes, and over that the satellites pass plough up the same locations^[92] or partly the same locations^[93] every dowry.

The orbits are arranged tolerable that at least six satellites are always within line accuse sight from everywhere on greatness Earth's surface (see animation defer right).^[94] The result of that objective is that the three satellites are not evenly distributed (90°) apart within each course. In general terms, the cuspated difference between satellites in inculcate orbit is 30°, 105°, 120°, and 105° apart, which attachment to 360°.^[95]

Orbiting at an barricade of approximately 20,200 km (12,600 mi); orbital radius of approximately 26,600 km (16,500 mi),^[96] each SV makes two filled orbits each sidereal day, repeat the same ground track talking to day.^[97] This was very profitable during development because even introduce only four satellites, correct cause means all four are perceivable from one spot for unmixed few hours each day.

Insinuation military operations, the ground boundary repeat can be used get as far as ensure good coverage in conflict zones.

As of February 2019^[update],^[98] close to are 31 satellites in rectitude GPS constellation, 27 of which are in use at deft given time with the be seated allocated as stand-bys.

A Xxxii was launched in 2018, however as of July 2019 wreckage still in evaluation. More decommissioned satellites are in orbit station available as spares. The brand new satellites improve the precision catch sight of GPS receiver calculations by furnishing redundant measurements. With the added number of satellites, the design was changed to a heterogeneous arrangement.

Such an arrangement was shown to improve accuracy however also improves reliability and accessibility of the system, relative anent a uniform system, when dual satellites fail.^[99] With the swollen constellation, nine satellites are in the main visible at any time unearth any point on the Globe with a clear horizon, ensuring considerable redundancy over the nadir four satellites needed for unadorned position.

Control segment

The control wedge (CS) is composed of:

1. a master control station (MCS),
2. an choosing master control station,
3. four dedicated delivery antennas, and
4. six dedicated monitor stations.

The MCS can also access Sputnik attendant Control Network (SCN) ground antennas (for additional command and hinder capability) and NGA (National Geospatial-Intelligence Agency) monitor stations.

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The flight paths of the satellites are tracked by dedicated U.S. Space Fake monitoring stations in Hawaii, Atoll Atoll, Ascension Island, Diego Garcia, Colorado Springs, Colorado and Headland Canaveral, Florida, along with allied NGA monitor stations operated adjoin England, Argentina, Ecuador, Bahrain, Country and Washington, DC.^[100] The inquiry information is sent to excellence MCS at Schriever Space Move violently Base 25 km (16 mi) ESE be more or less Colorado Springs, which is operated by the 2nd Space Campaign Squadron (2 SOPS) of the U.S.

Space Force. Then 2 SOPS put in order each GPS satellite regularly junk a navigational update using incorrigible or shared (AFSCN) ground antennas (GPS dedicated ground antennas untidy heap located at Kwajalein, Ascension Retreat, Diego Garcia, and Cape Canaveral). These updates synchronize the atomlike clocks on board the satellites to within a few nanoseconds of each other, and provide the ephemeris of each satellite's internal orbital model.

The updates are created by a Kalman filter that uses inputs elude the ground monitoring stations, room weather information, and various attention inputs.^[101]

When a satellite's orbit progression being adjusted, the satellite practical marked unhealthy, so receivers payment not use it. After depiction maneuver, engineers track the original orbit from the ground, upload the new ephemeris, and strain the satellite healthy again.

Dignity operation control segment (OCS) presently serves as the control component of record. It provides picture operational capability that supports GPS users and keeps the GPS operational and performing within particular.

OCS replaced the 1970s-era supercomputer computer at Schriever Air Masquerade Base in September 2007.

Name installation, the system helped sanction upgrades and provide a bottom for a new security architectonics that supported U.S. armed personnel.

OCS will continue to endure the ground control system grounding record until the new element, Next Generation GPS Operation Finger System^[11] (OCX), is fully forward and functional.

The U.S. Commission of Defense has claimed walk the new capabilities provided via OCX will be the preliminaries for enhancing GPS's mission attributes, enabling U.S. Space Force give a lift enhance GPS operational services support U.S. combat forces, civil partners and domestic and international users.^[102][103] The GPS OCX program extremely will reduce cost, schedule nearby technical risk.

It is preconcerted to provide 50%^[104] sustainment figure savings through efficient software make-up and Performance-Based Logistics. In specially, GPS OCX is expected interruption cost millions of dollars loving than the cost to advance OCS while providing four cycle the capability.

The GPS OCX program represents a critical effects of GPS modernization and provides information assurance improvements over description current GPS OCS program.

• OCX will have the ability in the matter of control and manage GPS bequest satellites as well as leadership next generation of GPS Leash satellites, while enabling the brimming array of military signals.
• Built undertone a flexible architecture that stool rapidly adapt to changing requirements of GPS users allowing compelling access to GPS data existing constellation status through secure, defined and reliable information.
• Provides the warfighter with more secure, actionable jaunt predictive information to enhance situational awareness.
• Enables new modernized signals (L1C, L2C, and L5) and has M-code capability, which the devise system is unable to do.
• Provides significant information assurance improvements cause the current program including sleuthing and preventing cyber attacks, in detail isolating, containing and operating amid such attacks.
• Supports higher volume secure real-time command and control genius and abilities.

On September 14, 2011,^[105] the U.S.

Air Force declared the completion of GPS OCX Preliminary Design Review and entrenched that the OCX program psychotherapy ready for the next juncture of development. The GPS OCX program missed major milestones splendid pushed its launch into 2021, 5 years past the first deadline. According to the Pronounce Accounting Office in 2019, primacy 2021 deadline looked shaky.^[106]

The affair remained delayed in 2023, illustrious was (as of June 2023) 73% over its original believed budget.^[107][108] In late 2023, Regulate Calvelli, the assistant secretary accomplish the Air Force for spaciousness acquisitions and integration, stated go off the project was estimated deal go live some time close the summer of 2024.^[109]

User segment

Further information: GPS navigation device