satellite constellation

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).

File:Flare at Paranal.jpg. Satellite constellations could have an impact on ground-based astronomy.{{cite web |title=On the increasing number of satellite constellations |url=https://www.eso.org/public/announcements/ann19029/ |website=www.eso.org |access-date=10 June 2019 |language=en}}]]

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.[https://www.satelliteevolutiongroup.com/articles/LEO-Constellations&Tracking.pdf LEO constellations and tracking challenges] Satellite Evolution Group, September 2017, Accessed 26 March 2021 The propagation delay for a round-trip internet protocol transmission via a geostationary satellite can be over 600{{nbsp}}ms, but as low as 125{{nbsp}}ms for a MEO satellite or 30{{nbsp}}ms for a LEO system.[https://www.telesat.com/wp-content/uploads/2020/07/Real-Time-Latency-Rethinking-Remote-Networks.pdf Real-Time Latency: Rethinking Remote Networks] {{Webarchive|url=https://web.archive.org/web/20210721082728/https://www.telesat.com/wp-content/uploads/2020/07/Real-Time-Latency-Rethinking-Remote-Networks.pdf |date=2021-07-21 }} Telesat, February 2020, Accessed 26 March 2021

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.

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

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.J. G. Walker, Satellite constellations, Journal of the British Interplanetary Society, vol. 37, pp. 559-571, 1984 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°:{{nbsp}}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.A. H. Ballard, Rosette Constellations of Earth Satellites, IEEE Transactions on Aerospace and Electronic Systems, Vol 16 No. 5, Sep. 1980.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. Ballard's notation is (t,p,m) where m is a multiple of the fractional offset between planes.

File:Walker-Star Constellation.webp

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°:{{nbsp}}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.

In spaceflight, an orbital shell is a set of artificial satellites in circular orbits at a certain fixed altitude.[https://fcc.report/IBFS/SAT-MOD-20181108-00083/1569860 SPACEX NON-GEOSTATIONARY SATELLITE SYSTEM, Attachment A, TECHNICAL INFORMATION TO SUPPLEMENT SCHEDULE S], US Federal Communications Commission, 8 November 2018, accessed 19 November 2019. 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).{{citation needed|date=November 2019}}

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.{{citation needed|date=November 2019}}

Several existing satellite constellations typically use a single orbital shell. New large megaconstellations have been proposed that consist of multiple orbital shells.{{Cite web|url=https://spacenews.com/amazon-lays-out-constellation-service-goals-deployment-and-deorbit-plans-to-fcc/|title=Amazon lays out constellation service goals, deployment and deorbit plans to FCC|date=2019-07-08|website=SpaceNews.com|language=en-US|access-date=2019-11-22}}

{{Main article|Satellite navigation}}

{{See also|Satellite communication|Category:Communications satellite constellations}}

• Sirius Satellite Radio
• XM Satellite Radio
• SES
• Othernet
• Molniya (discontinued)

• Spire (AIS, ADS-B)
• Iridium (AIS, ADS-B, IoT)
• Myriota (IoT)
• Swarm Technologies (IoT)
• Astrocast (IoT)
• TDRSS

Other Internet access systems are proposed or currently being developed:

Some systems were proposed but never realized:

{{notelist}}

; Progress

• Boeing Satellite is transferring the application to OneWeb{{cite web|url=https://advanced-television.com/2017/12/11/boeing-wants-to-help-oneweb-satellite-plans/|title=Boeing wants to help OneWeb satellite plans|date=2017-12-17|publisher=Advanced Television|access-date=2018-10-21}}
• LeoSat shut down completely in 2019{{cite magazine |url=https://spacenews.com/leosat-absent-investors-shuts-down/ |title=LeoSat, absent investors, shuts down|magazine=Space News}}
• The OneWeb constellation had 6 pilot satellites in February 2019, 74 satellites launched as of 21 March 2020{{cite news|url=https://www.bbc.com/news/science-environment-51991325|title=OneWeb increases mega-constellation to 74 satellites|date=2020-03-21|access-date=2020-04-07}} but filed for bankruptcy on 27 March 2020{{cite news|url=https://news.yahoo.com/coronavirus-oneweb-blames-coronavirus-collapse-090027262.html|title=Coronavirus: OneWeb blames pandemic for collapse|date=2020-03-30|access-date=2020-04-07}}{{cite web |url=https://casedocs.omniagentsolutions.com/cmsvol2/pub_47378/808974_437-1.pdf |title=Voluntary Petition for Non-Individuals Filing for Bankruptcy |website=Omni Agent Solutions |date=2020-03-27|access-date=2020-04-07}}
• Starlink: first mission (Starlink 0) launched on 24 May 2019; 955 satellites launched, 51 deorbited, 904 in orbit {{as of|2020|11|25|lc=on|df=UK}}; public beta test in limited latitude range started in November 2020{{cite news|url=https://www.space.com/spacex-invites-starlink-internet-beta-testing|title=SpaceX opens Starlink satellite internet to public beta testers: report|author=Samantha Mathewson|date=6 November 2020}}
• O3b mPOWER: first 6 satellites launched December 2022-November 2023 with service start April 2024. 7 more in 2024–2026.[https://www.satellitetoday.com/connectivity/2024/04/24/ses-o3b-mpower-meo-system-is-now-operational-service-rollout-to-follow/ SES’ O3b mPOWER MEO System is Now Operational, Service Rollout to Follow] Via Satellite. 24 April 2024. Accessed 29 April 2025
• Telesat LEO: two prototypes: 2018 launch
• CASIC Hongyun: prototype launched in December 2018{{cite news |url=https://www.nasaspaceflight.com/2018/12/chinese-long-march-11-launches-hongyun-satellite/ |title=Chinese Long March 11 launches with the first Hongyun satellite |work=NASASpaceFlight.com |first=Rui C. |last=Barbosa |date=21 December 2018 |access-date=24 December 2018}}
• CASC Hongyan prototype launched in December 2018,{{cite news |url=https://www.nasaspaceflight.com/2018/12/long-march-2d-20-hongyan-1-launch/ |title=Long March 2D concludes 2018 campaign with Hongyan-1 launch |work=NASASpaceFlight.com |first=Rui |last=Barbosa |date=29 December 2018 |access-date=29 December 2018}} might be merged with Hongyun{{cite tweet |user=Cosmic_Penguin |number=1205840577012518913 |title=Notice that these satellites from CASC are mentioned as part of a "national satellite Internet system". There are rumors that several of the planned Chinese private LEO comsat constellations have been recently absorbed into one big nationalized one. |date=14 December 2019 |access-date=16 December 2019}}
• Project Kuiper: FCC filing in July 2019. Prototypes launched in October 2023.

{{See also|List of Earth observation satellites}}

• RADARSAT Constellation
• Planet Labs
• Pléiades 1A and 1B
• Satellogic
• RapidEye
• Disaster Monitoring Constellation
• A-train
• SPOT 6 and SPOT 7
• Spire
• Synspective

{{Wikisource|Category:Satellite constellations|Satellite constellations}}

• Satellite internet constellation
• Light pollution
• Space debris
• Types of geocentric orbit
• Orbital mechanics

{{notelist}}

{{reflist}}

{{Commons category}}

Satellite constellation simulation tools:

• [http://www.avmdynamics.com/index1.htm AVM Dynamics Satellite Constellation Modeler]
• [http://savi.sourceforge.net/ SaVi Satellite Constellation Visualization]
• [http://www.transfinite.com/content/downloadsvisualyse.html Transfinite Visualyse Professional]

More information:

• [http://www.ee.surrey.ac.uk/Personal/L.Wood/publications/PhD-thesis/ Internetworking with satellite constellations - a PhD thesis (2001)]
• [http://www.ee.surrey.ac.uk/Personal/L.Wood/constellations/ Lloyd's satellite constellations] - last updated 20 July 2011
• [https://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5371741&newsearch=true&queryText=Examination%20and%20analysis%20of%20polar%20low%20earth%20orbit%20constellation Examination and analysis of polar low Earth orbit constellation-IEEE]

{{Satellite constellations}}

Category:Satellites

Category:Satellites by type