Satellite constellation/Overview

Overview


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.

Broadband applications benefit from low-latency communications, so 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.

Learning Task

 * Compare the satellite based services with ground based services for telecommunication. What are challenges, requirements and constraints in comparison. Discuss the topic in terms of
 * maintenance and operational robustness,
 * installation and productions,
 * operational costs,
 * coverage of areas,