Satellite navigation

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For maneuvering satellites to maintain orbit and station, see Orbital station-keeping.
U.S. Space Force's Global Positioning System
was the first global satellite navigation system and the first to be provided as a free global service.
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A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). As of 2023, five global systems are operational: the United States's Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), India's Indian Regional Navigation Satellite System (IRNSS), China's BeiDou Navigation Satellite System (BDS),[1] and the European Union's Galileo.[2]

EGNOS
, both based on GPS. Stand-alone operational regional navigation satellite systems (RNSS) include earlier generations of the BeiDou navigation system and the current Indian Regional Navigation Satellite System (IRNSS) or NavIC.[4]

Satellite navigation devices determine their location (longitude, latitude, and altitude/elevation) to high precision (within a few centimeters to meters) using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking). The signals also allow the electronic receiver to calculate the current local time to a high precision, which allows time synchronisation. These uses are collectively known as Positioning, Navigation and Timing (PNT). Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.

Global coverage for each system is generally achieved by a

orbital planes. The actual systems vary, but all use orbital inclinations of >50° and orbital periods
of roughly twelve hours (at an altitude of about 20,000 kilometres or 12,000 miles).

Classification

Further information: GNSS augmentation

GNSS systems that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:[5]

By their roles in the navigation system, systems can be classified as:

As many of the global GNSS systems (and augmentation systems) use similar frequencies and signals around L1, many "Multi-GNSS" receivers capable of using multiple systems have been produced. While some systems strive to interoperate with GPS as well as possible by providing the same clock, others do not.[8]

History

Further information:
GPS § History, GLONASS § History, GALILEO#History, and BeiDou § History

Ground based

fix
.

The first satellite navigation system was Transit, a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect: the satellites travelled on well-known paths and broadcast their signals on a well-known radio frequency. The received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position. Satellite orbital position errors are caused by radio-wave refraction, gravity field changes (as the Earth's gravitational field is not uniform), and other phenomena. A team, led by Harold L Jury of Pan Am Aerospace Division in Florida from 1970 to 1973, found solutions and/or corrections for many error sources.[citation needed] Using real-time data and recursive estimation, the systematic and residual errors were narrowed down to accuracy sufficient for navigation.[9]

Principles

Further information:
GPS § Navigation equations

Part of an orbiting satellite's broadcast includes its precise orbital data. Originally, the

US Naval Observatory (USNO) continuously observed the precise orbits of these satellites. As a satellite's orbit deviated, the USNO sent the updated information to the satellite. Subsequent broadcasts from an updated satellite would contain its most recent ephemeris
.

Modern systems are more direct. The satellite broadcasts a signal that contains orbital data (from which the position of the satellite can be calculated) and the precise time the signal was transmitted. Orbital data include a rough

GNSS positioning calculation
for details.

Each distance measurement, regardless of the system being used, places the receiver on a spherical shell at the measured distance from the broadcaster. By taking several such measurements and then looking for a point where they meet, a fix is generated. However, in the case of fast-moving receivers, the position of the signal moves as signals are received from several satellites. In addition, the radio signals slow slightly as they pass through the ionosphere, and this slowing varies with the receiver's angle to the satellite, because that changes the distance through the ionosphere. The basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centred on four satellites. Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.

Einstein's theory of general relativity is applied to GPS time correction, the net result is that time on a GPS satellite clock advances faster than a clock on the ground by about 38 microseconds per day.[10]

Applications

GNSS satellites used for navigation on a smartphone in 2021
Main article: GNSS applications
Further information: Automotive navigation system

The original motivation for satellite navigation was for military applications. Satellite navigation allows precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from mis-directed weapons. (See Guided bomb). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war.

Now a global navigation satellite system, such as Galileo, is used to determine users location and the location of other people or objects at any given moment. The range of application of satellite navigation in the future is enormous, including both the public and private sectors across numerous market segments such as science, transport, agriculture, insurance, energy, etc.[11][12]

The ability to supply satellite navigation signals is also the ability to deny their availability. The operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires.

Global navigation satellite systems

geostationary orbit (and its graveyard orbit), with the Van Allen radiation belts and the Earth to scale.[a]
The Moon's orbit is around 9 times as large as geostationary orbit.[b] (In the SVG file,
hover over an orbit or its label to highlight it; click to load its article.)
Launched GNSS satellites 1978 to 2014

In order of first launch year:

GPS

Main article: Global Positioning System

First launch year: 1978

The United States' Global Positioning System (GPS) consists of up to 32

orbital planes
. The exact number of satellites varies as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is the world's most utilized satellite navigation system.

GLONASS

Main article: GLONASS

First launch year: 1982

The formerly Soviet, and now Russian, Global'naya Navigatsionnaya Sputnikovaya Sistema, (GLObal NAvigation Satellite System or GLONASS), is a space-based satellite navigation system that provides a civilian radionavigation-satellite service and is also used by the Russian Aerospace Defence Forces. GLONASS has full global coverage since 1995 and with 24 active satellites.

BeiDou

Main article:
BeiDou Navigation Satellite System

First launch year: 2000

BeiDou started as the now-decommissioned Beidou-1, an Asia-Pacific local network on the geostationary orbits. The second generation of the system BeiDou-2 became operational in China in December 2011.[13] The BeiDou-3 system is proposed to consist of 30 MEO satellites and five geostationary satellites (IGSO). A 16-satellite regional version (covering Asia and Pacific area) was completed by December 2012. Global service was completed by December 2018.[14] On 23 June 2020, the BDS-3 constellation deployment is fully completed after the last satellite was successfully launched at the Xichang Satellite Launch Center.[15]

Galileo

Main article: Galileo (satellite navigation)

First launch year: 2011

The

modernized GPS system. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy. The full Galileo constellation consists of 24 active satellites,[20] the last of which was launched in December 2021.[21][22] The main modulation used in Galileo Open Service signal is the Composite Binary Offset Carrier
(CBOC) modulation.

Regional navigation satellite systems

NavIC

Main article:
NavIC

The NavIC or NAVigation with Indian Constellation is an autonomous regional satellite navigation system developed by the

space segment, ground segment and user receivers all being built in India.[26]

The constellation was in orbit as of 2018, and the system was available for public use in early 2018.[27] NavIC provides two levels of service, the "standard positioning service", which will be open for civilian use, and a "restricted service" (an encrypted one) for authorized users (including military). There are plans to expand NavIC system by increasing constellation size from 7 to 11.[28]

India plans to make the NAVIC global by adding 24 more MEO satellites. The Global NavIC will be free to use for the global public.[29]

Early BeiDou

Main articles:
BeiDou-2

The first two generations of China's BeiDou navigation system were designed to provide regional coverage.

Augmentation

Multi-functional Satellite Augmentation System, Differential GPS, GPS-aided GEO augmented navigation (GAGAN) and inertial navigation systems
.

QZSS

Main article: Quasi-Zenith Satellite System

The Quasi-Zenith Satellite System (QZSS) is a four-satellite regional

Asia-Oceania regions. QZSS services were available on a trial basis as of January 12, 2018, and were started in November 2018. The first satellite was launched in September 2010.[30] An independent satellite navigation system (from GPS) with 7 satellites is planned for 2023.[31]

EGNOS

This section is an excerpt from European Geostationary Navigation Overlay Service.[edit]
Map of the EGNOS ground network

The

GPS by reporting on the reliability and accuracy of their positioning data and sending out corrections. The system will supplement Galileo
in a future version.

EGNOS consists of 40 Ranging Integrity Monitoring Stations, 2 Mission Control Centres, 6 Navigation Land Earth Stations, the EGNOS Wide Area Network (EWAN), and 3

geostationary satellites.[32] Ground stations determine the accuracy of the satellite navigation systems data and transfer it to the geostationary satellites; users may freely obtain this data from those satellites using an EGNOS-enabled receiver, or over the Internet. One main use of the system is in aviation
.

According to specifications, horizontal position accuracy when using EGNOS-provided corrections should be better than seven metres. In practice, the horizontal position accuracy is at the metre level.

Similar service is provided in North America by the

Multi-functional Satellite Augmentation System (MSAS) and India's GPS-aided GEO augmented navigation
(GAGAN).

Galileo and EGNOS budget for the 2021–2027 period is €9 billion[33]

Comparison of systems

System
BeiDou
 Galileo GLONASS GPS NavIC QZSS
Owner China
European Union
 Russia United States India Japan
Coverage Global Global Global Global Regional Regional
Coding
CDMA
CDMA
CDMA
CDMA
CDMA
CDMA
Altitude 21,150 km (13,140 mi) 23,222 km (14,429 mi) 19,130 km (11,890 mi) 20,180 km (12,540 mi) 36,000 km (22,000 mi) 32,600 km (20,300 mi) –
39,000 km (24,000 mi)[34]
Period 12.88 h (12 h 53 min) 14.08 h (14 h  5 min) 11.26 h (11 h 16 min) 11.97 h (11 h 58 min) 23.93 h (23 h 56 min) 23.93 h (23 h 56 min)
Rev./
S. day
 13/7 (1.86) 17/10 (1.7) 17/8 (2.125) 2 1 1
Satellites BeiDou-3:
28 operational
(24 MEO, 3 IGSO, 1 GSO)
5 in orbit validation
2 GSO planned 20H1
BeiDou-2:
15 operational
1 in commissioning 		By design:

27 operational + 3 spares

Currently:

26 in orbit
24 operational

2 inactive
6 to be launched[35]

24 by design
24 operational
1 commissioning
1 in flight tests[36] 		24 by design
30 operational[37] 		8 operational
(3 GEO, 5
GSO
MEO) 		4 operational (3 GSO, 1 GEO)
7 in the future
Frequency 1.561098 GHz (B1)
1.589742 GHz (B1-2)
1.20714 GHz (B2)
1.26852 GHz (B3) 		1.559–1.592 GHz (E1)
1.164–1.215 GHz (E5a/b)
1.260–1.300 GHz (E6) 		1.593–1.610 GHz (G1)
1.237–1.254 GHz (G2)
1.189–1.214 GHz (G3) 		1.563–1.587 GHz (L1)
1.215–1.2396 GHz (L2)
1.164–1.189 GHz (L5) 		1.17645 GHz(L5)
2.492028 GHz (S) 		1.57542 GHz (L1C/A, L1C, L1S)
1.22760 GHz (L2C)
1.17645 GHz (L5, L5S)
1.27875 GHz (L6)[38]
Status Operational[39] Operating since 2016
2020 completion[35] 		Operational Operational Operational Operational
Accuracy 3.6 metres (12 ft) (public)
0.1 metres (0.33 ft) (encrypted) 		0.2 metres (0.66 ft) (public)
0.01 metres (0.033 ft) (encrypted) 		2–4 metres (6.6–13.1 ft) 0.3–5 metres (0.98–16.40 ft)
(no DGPS or WAAS) 		1 metre (3.3 ft) (public)
0.1 metres (0.33 ft) (encrypted) 		1 metre (3.3 ft) (public)
0.1 metres (0.33 ft) (encrypted)
System
BeiDou
 Galileo GLONASS GPS NavIC QZSS

Sources:[7][40]

Using multiple GNSS systems for user positioning increases the number of visible satellites, improves precise point positioning (PPP) and shortens the average convergence time.[41] The signal-in-space ranging error (SISRE) in November 2019 were 1.6 cm for Galileo, 2.3 cm for GPS, 5.2 cm for GLONASS and 5.5 cm for BeiDou when using real-time corrections for satellite orbits and clocks.[42] The average SISREs of the BDS-3 MEO, IGSO, and GEO satellites were 0.52 m, 0.90 m and 1.15 m, respectively. Compared to the four major global satellite navigation systems consisting of MEO satellites, the SISRE of the BDS-3 MEO satellites was slightly inferior to 0.4 m of Galileo, slightly superior to 0.59 m of GPS, and remarkably superior to 2.33 m of GLONASS. The SISRE of BDS-3 IGSO was 0.90 m, which was on par with the 0.92 m of QZSS IGSO. However, as the BDS-3 GEO satellites were newly launched and not completely functioning in orbit, their average SISRE was marginally worse than the 0.91 m of the QZSS GEO satellites.[3]

Related techniques

Further information: Satellite geodesy § Radio techniques

DORIS

Main article:
DORIS (geodesy)

Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a French precision navigation system. Unlike other GNSS systems, it is based on static emitting stations around the world, the receivers being on satellites, in order to precisely determine their orbital position. The system may be used also for mobile receivers on land with more limited usage and coverage. Used with traditional GNSS systems, it pushes the accuracy of positions to centimetric precision (and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of Earth rotation and deformations), in order to build a much more precise geodesic reference system.[43]

LEO satellites

The two current operational

AT commands or a graphical user interface.[44][45]
This can also be used by the gateway to enforce restrictions on geographically bound calling plans.

International regulation

The

radiodetermination-satellite service used for the purpose of radionavigation. This service may also include feeder links necessary for its operation".[46]

RNSS is regarded as a safety-of-life service and an essential part of navigation which must be protected from interferences.

Aeronautical radionavigation-satellite (short: ARNSS) is – according to Article 1.47 of the

earth stations
are located on board aircraft.»

Maritime radionavigation-satellite service (short: MRNSS) is – according to Article 1.45 of the

radionavigation-satellite service
in which earth stations are located on board ships.»

Classification

ITU Radio Regulations (article 1) classifies radiocommunication services as:

  • Radiodetermination service
    (article 1.40)
  • Radiodetermination-satellite service
    (article 1.41)
  • Radionavigation service
    (article 1.42)
    • Radionavigation-satellite service (article 1.43)
    • Maritime radionavigation service
      (article 1.44)
      • Maritime radionavigation-satellite service
        (article 1.45)
    • Aeronautical radionavigation service
      (article 1.46)
      • Aeronautical radionavigation-satellite service
        (article 1.47)
Examples of RNSS use

Frequency allocation

Further information: Frequency allocation

The allocation of radio frequencies is provided according to Article 5 of the ITU Radio Regulations (edition 2012).[49]

To improve harmonisation in spectrum utilisation, most service allocations are incorporated in national Tables of Frequency Allocations and Utilisations within the responsibility of the appropriate national administration. Allocations are:

  • primary: indicated by writing in capital letters
  • secondary: indicated by small letters
  • exclusive or shared utilization: within the responsibility of administrations.
Allocation to services
Region 1
      Region 2           Region 3     
5 000–5 010 MHz
AERONAUTICAL MOBILE-SATELLITE (R)
AERONAUTICAL RADIONAVIGATION
RADIONAVIGATION-SATELLITE (Earth-to-space)

See also

Notes

  1. ^ Orbital periods and speeds are calculated using the relations 4π2R3 = T2GM and V2R = GM, where R is the radius of orbit in metres; T is the orbital period in seconds; V is the orbital speed in m/s; G is the gravitational constant, approximately 6.673×10−11 Nm2/kg2; M is the mass of Earth, approximately 5.98×1024 kg (1.318×1025 lb).
  2. ^ Approximately 8.6 times (in radius and length) when the Moon is nearest (that is, 363,104 km/42,164 km), to 9.6 times when the Moon is farthest (that is, 405,696 km/42,164 km).

References

  1. ^ "China's GPS rival Beidou is now fully operational after final satellite launched". cnn.com. 24 June 2020. Retrieved 2020-06-26.
  2. ^ "Galileo is the European global satellite-based navigation system". www.euspa.europa.eu. 26 January 2024. Retrieved 26 January 2024.
  3. ^ a b c Kriening, Torsten (23 January 2019). "Japan Prepares for GPS Failure with Quasi-Zenith Satellites". SpaceWatch.Global. Retrieved 10 August 2019.
  4. ^ Indian Satellite Navigation Policy - 2021 (Draft) (PDF). Bengaluru, India: Department of Space. 2021. p. 7. Archived from the original (PDF) on 30 July 2021. Retrieved 27 July 2022. ISRO/DOS shall work towards expanding the coverage from regional to global to ensure availability of NavIC standalone signal in any part of the world without relying on other GNSS and aid in wide utilisation of Indian navigation system across the globe.
  5. ^ a b c d "A Beginner's Guide to GNSS in Europe" (PDF). IFATCA. Archived from the original (PDF) on 27 June 2017. Retrieved 20 May 2015.
  6. ^ "Galileo General Introduction - Navipedia". gssc.esa.int. Retrieved 2018-11-17.
  7. ^ a b "GNSS signal - Navipedia". gssc.esa.int. Retrieved 2018-11-17.
  8. hdl:11577/3269537
    .
  9. ^ Jury, H, 1973, Application of the Kalman Filter to Real-time Navigation using Synchronous Satellites, Proceedings of the 10th International Symposium on Space Technology and Science, Tokyo, 945-952.
  10. ^ "Relativistic Effects on the Satellite Clock". The Pennsylvania State University.
  11. ^ "Applications". www.gsa.europa.eu. 2011-08-18. Retrieved 2019-10-08.
  12. S2CID 258538772
    .
  13. ^ "China's GPS rival is switched on". BBC News. 2012-03-08. Retrieved 2020-06-23.
  14. ^ "The BDS-3 Preliminary System Is Completed to Provide Global Services". news.dwnews.com. Retrieved 2018-12-27.
  15. ^ "APPLICATIONS-Transport". en.beidou.gov.cn. Retrieved 2020-06-23.
  16. ^ "Galileo goes live!". europa.eu. 14 December 2016.
  17. ^ "Boost to Galileo sat-nav system". BBC News. 25 August 2006. Retrieved 2008-06-10.
  18. ^ "Commission awards major contracts to make Galileo operational early 2014". 2010-01-07. Retrieved 2010-04-19.
  19. ^ "GIOVE-A launch News". 2005-12-28. Retrieved 2015-01-16.
  20. ^ "Galileo begins serving the globe". INTERNATIONALES VERKEHRSWESEN (in German). 23 December 2016.
  21. ^ "Soyuz launch from Kourou postponed until 2021, 2 others to proceed". Space Daily. 19 May 2020.
  22. ^ "Galileo Initial Services". gsa.europa.eu. 9 December 2016. Retrieved 25 September 2020.
  23. ^ "India to develop its own version of GPS". Rediff.com. Retrieved 2011-12-30.
  24. ^ S. Anandan (2010-04-10). "Launch of first satellite for Indian Regional Navigation Satellite system next year". Beta.thehindu.com. Retrieved 2011-12-30.
  25. ^ "IRNSS Programme - ISRO". www.isro.gov.in. Archived from the original on 2022-03-02. Retrieved 2018-07-14.
  26. ^ "India to build a constellation of 7 navigation satellites by 2012". Livemint.com. 2007-09-05. Retrieved 2011-12-30.
  27. ^ Rohit KVN (28 May 2017). "India's own GPS IRNSS NavIC made by ISRO to go live in early 2018". International Business Times. Retrieved 29 April 2021.
  28. ^ IANS (2017-06-10). "Navigation satellite clocks ticking; system to be expanded: ISRO". The Economic Times. Retrieved 2018-01-24.
  29. ^ Koshy, Jacob (October 26, 2022). "ISRO to boost NavIC, widen user base of location system". The Hindu. Archived from the original on Sep 20, 2023.
  30. ^ "About QZSS". JAXA. Archived from the original on 2009-03-14. Retrieved 2009-02-22.
  31. ^ Henry, Caleb (15 May 2017). "Japan mulls seven-satellite QZSS system as a GPS backup". SpaceNews.com. Archived from the original on 9 Dec 2023. Retrieved 10 August 2019.
  32. ^ "EGNOS System". March 2016.
  33. ^ "EU space policy". www.consilium.europa.eu. Retrieved 2020-12-29.
  34. ^ Graham, William (9 October 2017). "Japan's H-2A conducts QZSS-4 launch". NASASpaceFlight.com. Archived from the original on 2017-10-10.
  35. ^ a b Irene Klotz; Tony Osborne; Bradley Perrett (Sep 12, 2018). "The Rise Of New Navigation Satellites". Aviation Week Network. Archived from the original on Oct 25, 2023.
  36. ^ "Information and Analysis Center for Positioning, Navigation and Timing". Archived from the original on 2018-07-21. Retrieved 2018-07-21.
  37. ^ "GPS Space Segment". Retrieved 2015-07-24.
  38. ^ "送信信号一覧". Retrieved 2019-10-25.
  39. ^ "China launches final satellite in GPS-like Beidou system". phys.org. Archived from the original on 24 June 2020. Retrieved 24 June 2020.
  40. ISBN 978-981-99-2074-7
    .
  41. S2CID 125213815
    .
  42. doi:10.1007/s10291-020-01026-6
    .
  43. ^ "DORIS information page". Jason.oceanobs.com. Retrieved 2011-12-30.
  44. ^ "Globalstar GSP-1700 manual" (PDF). Archived from the original (PDF) on 2011-07-11. Retrieved 2011-12-30.
  45. ^ Rickerson, Don (January 2005). "Iridium SMS and SBD" (PDF). Personal Satellite Network, Inc. Archived from the original (PDF) on 9 November 2005.
  46. ^ ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.43, definition: radionavigation-satellite service
  47. ^ ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.47, definition: aeronautical radionavigation service
  48. ^ ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.45, definition: maritime radionavigation-satellite service
  49. ^ ITU Radio Regulations, CHAPTER II – Frequencies, ARTICLE 5 Frequency allocations, Section IV – Table of Frequency Allocations

Further reading

External links

Information on specific GNSS systems

Organizations related to GNSS

Supportive or illustrative sites

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