Satellite constellation

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Template:Short description

File:GPS24goldenSML.gif
The GPS constellation calls for 24 satellites to be distributed equally among six orbital planes. Notice how the number of satellites in view from a given point on the Earth's surface, in this example at 40°N, changes with time.

A satellite constellation is a group of artificial satellites working together as a system. Unlike a single satellite, a constellation can provide permanent global or near-global coverage, such that at any time everywhere on Earth at least one satellite is visible. Satellites are typically placed in sets of complementary orbital planes and connect to globally distributed ground stations. They may also use inter-satellite communication.

Other satellite groups

Satellite constellations should not be confused with:

  • satellite clusters, which are groups of satellites moving very close together in almost identical orbits (see satellite formation flying);
  • satellite series or satellite programs (such as Landsat), which are generations of satellites launched in succession;
  • satellite fleets, which are groups of satellites from the same manufacturer or operator that function independently from each other (not as a system).

Overview

File:Flare at Paranal.jpg
A bright artificial satellite flare is visible above the Very Large Telescope. Satellite constellations could have an impact on ground-based astronomy.[1]

Satellites in medium Earth orbit (MEO) and low Earth orbit (LEO) are often deployed in satellite constellations, because the coverage area provided by a single satellite only covers a small area that moves as the satellite travels at the high angular velocity needed to maintain its orbit. Many MEO or LEO satellites are needed to maintain continuous coverage over an area. This contrasts with geostationary satellites, where a single satellite, at a much higher altitude and moving at the same angular velocity as the rotation of the Earth's surface, provides permanent coverage over a large area.

For some applications, in particular digital connectivity, the lower altitude of MEO and LEO satellite constellations provide advantages over a geostationary satellite, with lower path losses (reducing power requirements and costs) and latency.[2] The propagation delay for a round-trip internet protocol transmission via a geostationary satellite can be over 600Script error: No such module "String".ms, but as low as 125Script error: No such module "String".ms for a MEO satellite or 30Script error: No such module "String".ms for a LEO system.[3]

Examples of satellite constellations include the Global Positioning System (GPS), Galileo and GLONASS constellations for navigation and geodesy in MEO, the Iridium and Globalstar satellite telephony services and Orbcomm messaging service in LEO, the Disaster Monitoring Constellation and RapidEye for remote sensing in Sun-synchronous LEO, Russian Molniya and Tundra communications constellations in highly elliptic orbit, and satellite broadband constellations, under construction from Starlink and OneWeb in LEO, and operational from O3b in MEO.

Design

Walker Constellation

There are a large number of constellations that may satisfy a particular mission. Usually constellations are designed so that the satellites have similar orbits, eccentricity and inclination so that any perturbations affect each satellite in approximately the same way. In this way, the geometry can be preserved without excessive station-keeping thereby reducing the fuel usage and hence increasing the life of the satellites. Another consideration is that the phasing of each satellite in an orbital plane maintains sufficient separation to avoid collisions or interference at orbit plane intersections.

File:Walker-Delta Constellation.webp
Walker-Delta Constellation

A class of circular orbit geometries that has become popular is the Walker Delta Pattern constellation. This has an associated notation to describe it which was proposed by John Walker.[4] His notation is:

i: t/p/f

where:

  • i is the inclination;
  • t is the total number of satellites;
  • p is the number of equally spaced planes; and
  • f is the relative spacing between satellites in adjacent planes. The change in true anomaly (in degrees) for equivalent satellites in neighbouring planes is equal to f × 360 / t.

For example, the Galileo navigation system is a Walker Delta 56°:Script error: No such module "String".24/3/1 constellation. This means there are 24 satellites in 3 planes inclined at 56 degrees, spanning the 360 degrees around the equator. The "1" defines the phasing between the planes, and how they are spaced. The Walker Delta is also known as the Ballard rosette, after A. H. Ballard's similar earlier work.[5][6] Ballard's notation is (t,p,m) where m is a multiple of the fractional offset between planes.

File:Walker-Star Constellation.webp
Walker-Star Constellation

Another popular constellation type is the near-polar Walker Star, which is used by Iridium. Here, the satellites are in near-polar circular orbits across approximately 180 degrees, travelling north on one side of the Earth, and south on the other. The active satellites in the full Iridium constellation form a Walker Star of 86.4°:Script error: No such module "String".66/6/2, i.e. the phasing repeats every two planes. Walker uses similar notation for stars and deltas, which can be confusing.

These sets of circular orbits at constant altitude are sometimes referred to as orbital shells.

Orbital shell

In spaceflight, an orbital shell is a set of artificial satellites in circular orbits at a certain fixed altitude.[7] In the design of satellite constellations, an orbital shell usually refers to a collection of circular orbits with the same altitude and, oftentimes, orbital inclination, distributed evenly in celestial longitude (and mean anomaly).Script error: No such module "Unsubst". For a sufficiently high inclination and altitude the orbital shell covers the entire orbited body. In other cases the coverage extends up to a certain maximum latitude.Script error: No such module "Unsubst".

Several existing satellite constellations typically use a single orbital shell. New large megaconstellations have been proposed that consist of multiple orbital shells.[7][8]

List of satellite constellations

Navigational satellite constellations

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Satellite constellations used for navigation
Name Operator Satellites and orbits
(latest design, excluding spares) 		Coverage Services Status Years in service
Global Positioning System (GPS) USSF 24 in 6 planes at 20,180 km (55° MEO) Global Navigation Operational 1993–present
GLONASS Roscosmos 24 in 3 planes at 19,130 km (64°8' MEO) Global Navigation Operational 1995–present
Galileo EUSPA, ESA 24 in 3 planes at 23,222 km (56° MEO) Global Navigation Operational 2019–present
BeiDou CNSA Template:Ubl Global Navigation Operational Template:Ubl
NAVIC ISRO Template:Ubl Regional Navigation Operational 2018–present
QZSS JAXA Template:Ubl Regional Navigation Operational 2018–present

Communications satellite constellations

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Broadcasting

Monitoring

Internet access

Operational communications satellite constellations
Name Operator Constellation design Coverage Freq. Services
Broadband Global Area Network (BGAN) Inmarsat 3 geostationary satellites 82°S to 82°N Internet access
Global Xpress (GX) Inmarsat 5 Geostationary satellites[9] Ka band Internet access
Globalstar Globalstar 48 at 1400 km, 52° (8 planes)[10] 70°S to 70°N[10] Internet access, satellite telephony
Iridium Iridium Communications 66 at 780 km, 86.4° (6 planes) Global Template:Ubl Internet access, satellite telephony
O3b SES 20 at 8,062 km, 0° (circular equatorial orbit) 45°S to 45°N Ka band Internet access
O3b mPOWER SES 8 at 8,062 km, 0° (circular equatorial orbit)
5 more to be launched by end 2026 		45°S to 45°N Ka (26.5–40 GHz) Internet access
Orbcomm ORBCOMM 17 at 750 km, 52° (OG2) 65°S to 65°N IoT and M2M, AIS
Defense Satellite Communications System (DSCS) 4th Space Operations Squadron Military communications
Wideband Global SATCOM (WGS) 4th Space Operations Squadron 10 geostationary satellites Military communications
ViaSat Viasat, Inc. 4 geostationary satellites Varying Internet access
Eutelsat Eutelsat 20 geostationary satellites Commercial
Thuraya Thuraya 2 geostationary satellites EMEA and Asia L band Internet access, satellite telephony
Starlink SpaceX LEO in several orbital shellsTemplate:Ubl Template:Ubl Template:Ubl Internet access[11][12][13]
OneWeb constellation Eutelsat (completed merger in Sep 2023) 882–1980[14](planned)

Total number of operational satellites: 634 as of 20 May 2023

Global Template:Ubl Internet access

Other Internet access systems are proposed or currently being developed:

Proposed internet satellite constellations[15]
Constellation Manufacturer Number Weight Unveil. Avail. Altitude Offer Band Inter-sat.
links
IRIS² European Space Agency TBD TBD
Telesat LEO Template:Ubl 117–512[16] — 2016 2027 Template:Cvt Fiber-optic cable-like Ka (26.5–40 GHz) Optical[17][18]
Hongyun[19] CASIC 156 2017 2022 Template:Cvt
Hongyan[20] CASC 320-864[21] 2017 2023 Template:Cvt
Hanwha Systems[22] 2000 2022 2025
Project Kuiper Amazon 3236 2019 2024 Template:Cvt 56°S to 56°N[23]

Some systems were proposed but never realized:

Abandoned communication satellite constellation designs
Name Operator Constellation design Freq. Services Abandoned date
Celestri Motorola 63 satellites at 1400 km, 48° (7 planes) Ka band (20/30 GHz) Global, low-latency broadband Internet services 1998 May
Teledesic Teledesic Template:Ubl Ka band (20/30 GHz) 100 Mbit/s up, 720 Mbit/s down global internet access 2002 October
LeoSat Thales Alenia 78–108 satellites at 1400 km Ka (26.5–40 GHz) High-speed broadband internet 2019


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Progress

Earth observation satellite constellations

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See also

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Notes

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References

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  1. ↑ Script error: No such module "citation/CS1".
  2. ↑ LEO constellations and tracking challenges Satellite Evolution Group, September 2017, Accessed 26 March 2021
  3. ↑ Real-Time Latency: Rethinking Remote Networks Template:Webarchive Telesat, February 2020, Accessed 26 March 2021
  4. ↑ J. G. Walker, Satellite constellations, Journal of the British Interplanetary Society, vol. 37, pp. 559-571, 1984
  5. ↑ A. H. Ballard, Rosette Constellations of Earth Satellites, IEEE Transactions on Aerospace and Electronic Systems, Vol 16 No. 5, Sep. 1980.
  6. ↑ J. G. Walker, Comments on "Rosette constellations of earth satellites", IEEE Transactions on Aerospace and Electronic Systems, vol. 18 no. 4, pp. 723-724, November 1982.
  7. ↑ a b SPACEX NON-GEOSTATIONARY SATELLITE SYSTEM, Attachment A, TECHNICAL INFORMATION TO SUPPLEMENT SCHEDULE S, US Federal Communications Commission, 8 November 2018, accessed 19 November 2019.
  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ Script error: No such module "citation/CS1".
  10. ↑ a b Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "Citation/CS1".
  17. ↑ Script error: No such module "citation/CS1".
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ Script error: No such module "citation/CS1".
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "citation/CS1".
  23. ↑ Script error: No such module "citation/CS1".
  24. ↑ Script error: No such module "citation/CS1".
  25. ↑ Script error: No such module "Citation/CS1".
  26. ↑ Script error: No such module "citation/CS1".
  27. ↑ Script error: No such module "citation/CS1".
  28. ↑ Script error: No such module "citation/CS1".
  29. ↑ Script error: No such module "citation/CS1".
  30. ↑ SES’ O3b mPOWER MEO System is Now Operational, Service Rollout to Follow Via Satellite. 24 April 2024. Accessed 29 April 2025
  31. ↑ Script error: No such module "citation/CS1".
  32. ↑ Script error: No such module "citation/CS1".
  33. ↑ Template:Cite tweet

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External links

Template:Sister project Satellite constellation simulation tools:

More information:

Template:Satellite constellations

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