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Samples of three GPS satellites' orbits over a five-year period (2013 to 2018) USA-242 · USA-239 · USA-151 · Earth As of 22 January 2025, 83 Global Positioning System navigation satellites have been built: 31 are launched and operational, 3 are in reserve or testing, 43 are retired, 2 were lost during launch, and 1 prototype was never launched. 3 Block III satellites have completed ...
GPS Block III is the first series of third-generation GPS satellites, incorporating new signals and broadcasting at higher power levels. In September 2016, the United States Air Force awarded Lockheed Martin a contract option for two more Block III satellites, setting the total number of GPS III satellites to ten. [22]
The GPS date and time, and the satellite's status. The ephemeris: precise orbital information for the transmitting satellite. The almanac: status and low-resolution orbital information for every satellite. An ephemeris is valid for only four hours, while an almanac is valid–with little dilution of precision–for up to two weeks. [7]
The United States' Global Positioning System (GPS) consists of up to 32 medium Earth orbit satellites in six different orbital planes. The exact number of satellites varies as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is the world's most utilized satellite navigation system.
These are used for Global Navigation Satellite System spacecraft, such as GPS, GLONASS, Galileo, BeiDou. GPS satellites orbit at an altitude of 20,200 kilometers (12,600 mi) with an orbital period of almost 12 hours. [8] Geosynchronous orbit (GSO) and geostationary orbit (GEO) are orbits around Earth matching Earth's sidereal rotation period.
As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a seconds-into-week number. The week number is transmitted as a ten- bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit . There are many different ways to mathematically describe the same orbit, but certain schemes, each consisting of a set of six parameters, are commonly used in ...
In the context of GPS the most prominent correction introduced by general relativity is gravitational time dilation: the clocks located deeper in the gravitational potential well (i.e. closer to the attracting body) tick slower. Satellite clocks are slowed by their orbital speed but sped up by their distance out of the Earth's gravitational well.