The Interoperable Global Navigation Satellite Systems Space Service Volume

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The availability and performance of global navigation satellite systems (GNSS) signals at high altitude is documented as the GNSS Space Service Volume (SSV). While different definitions of the SSV exist and may continue to exist for the different service providers, within the context of this booklet it is defined as the region of space between 3,000 km and 36,000 km above the Earth’s surface, which is the geostationary altitude. For space users located at low altitudes (below 3,000 km), the GNSS signal reception is similar to that for terrestrial users and can be conservatively derived from the results presented for the lower SSV in this booklet.



Description of individual GNSS support to SSV

The Global Positioning System (GPS) is a United States-owned utility that provides users with positioning, navigation, and timing (PNT) services. GPS represents a “system of systems” consisting of three segments: a space segment, employing a nominal constellation of 24 space vehicles (SV) transmitting one-way signals with the GPS satellite’s position and time; a control segment consisting of a global network of ground facilities that track the GPS satellites, monitor their transmissions, perform analyses, and send commands and data to the constellation; and a user segment that consists of GPS receiver equipment, which receives the signals from at least four GPS satellites and uses the transmitted information to calculate in real-time the three dimensional position and the time. The United States Air Force develops, maintains, and operates the space and control segments. Official United States Government information about GPS and related data topics is available at the National Coordination Office (https://www.gps.gov/).


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