page_title: Satellite constellation
section_title: Overview
hierarchical_section_title: Satellite constellation / Overview
caption_attribution_description: English: A bright artificial satellite flare is visible above the Unit Telescopes of the VLT.
context_page_description: 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.
  Satellite constellations should not be confused with satellite clusters, which are groups of satellites moving very close together in almost identical orbits, satellite programs, which are generations of satellites launched in succession, and satellite fleets, which are groups of satellites from the same manufacturer or operator that function independently from each other.
context_section_description: Low Earth orbiting satellites (LEOs) are often deployed in satellite constellations, because the coverage area provided by a single LEO satellite only covers a small area that moves as the satellite travels at the high angular velocity needed to maintain its orbit.  Many LEO satellites are needed to maintain continuous coverage over an area. This contrasts with geostationary satellites, where a single satellite, moving at the same angular velocity as the rotation of the Earth's surface, provides permanent coverage over a large area.
  Examples of satellite constellations include the Global Positioning System (GPS), Galileo and GLONASS constellations for navigation and geodesy, the Iridium and Globalstar satellite telephony services, the Disaster Monitoring Constellation and RapidEye for remote sensing, the Orbcomm messaging service, Russian elliptic orbit Molniya and Tundra constellations, the large-scale Teledesic, Skybridge, and Celestri broadband constellation proposals of the 1990s, and more recent systems such as O3b or the OneWeb proposal.
  For applications which benefit from low-latency communications, LEO satellite constellations provide an advantage over a geostationary satellite, where minimum theoretical latency from ground to satellite is about 125 milliseconds, compared to 1–4 milliseconds for a LEO satellite.  A LEO satellite constellation can also provide more system capacity by frequency reuse across its coverage, with spot beam frequency use being analogous to the minimum number of satellites needed to provide a service, and their orbits—is a field in itself.
caption: A bright artificial satellite flare is visible above the VLT. Satellite constellations have an impact on ground-based astronomy.[1]
exif: {"Image ImageDescription": "A bright artificial satellite flare is visible above the Unit Telescopes of the VLT.", "Image Software": "Adobe Photoshop CC (Windows)", "Image Artist": "Roger Wesson / World Traveller Photography"}