Global Positioning Service (GPS) satellite orbiting altitude is:

12,554 miles.

Actually, it is 12,550 miles, or 20,200 kilometers.

The GPS system depends on 24 satellites orbiting Earth. When you use GPS, it picks up signals from any direct line satellite, with at least four satellites' signals to derive the position.

For more details, please see the GPS gov site, for the article Space Segment

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The GPS transmitted frequencies are:

1227.6 MHz and 1575.4 MHz.

From kd9fni:

L1 (1575.42 Mhz) and L2 (1227.60 MHz)

The federal site GPS.gov, lists a page of Technical Documentation links. The subpage for the Interface Control Documents contains the link to document IS-GPS-200, Revision M, 05/21/2012 the latest.

It defines the requirements related to the Interface between the GPS and user segments for radio frequency link 1 (L1) and Link 2 (L2).

It is a pdf document of 245 pages. On the pdf page 32, document page 12, it lists 3.3.1.1 Frequency Plan.

It states, "The nominal carrier frequencies (f0) shall be 1575.42 MHz, and 1227.6 MHz for L1 and L2, respectively."

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How many GPS satellites are normally in operation?

24

From GPS.gov:

The United States is committed to maintaining the availability of at least 24 operational GPS satellites, 95% of the time.

The satellites in the GPS constellation are arranged into six equally-spaced orbital planes surrounding the Earth. Each plane contains four "slots" occupied by baseline satellites.

This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.

For more details, please see the GPS gov site, the Official U.S. government information about the Global Positioning System (GPS) and related topics, for the article Space Segment,

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What best describes the GPS Satellites orbits?

They are in six orbital planes equally spaced and inclined about 55 degrees to the equator.

From GPS.gov:

The United States is committed to maintaining the availability of at least 24 operational GPS satellites, 95% of the time.

The satellites in the GPS constellation are arranged into six equally-spaced orbital planes surrounding the Earth. Each plane contains four "slots" occupied by baseline satellites.

This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.

For more details, please see the GPS gov site, the Official U.S. government information about the Global Positioning System (GPS) and related topics, for the article Space Segment, And for application of GPS in Marine industry, please see article Marine

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How many satellites must be received to provide complete position and time?

4

From GPS.gov:

The United States is committed to maintaining the availability of at least 24 operational GPS satellites, 95% of the time.

The satellites in the GPS constellation are arranged into six equally-spaced orbital planes surrounding the Earth. Each plane contains four "slots" occupied by baseline satellites.

This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.

For more details, please see the GPS gov site, the Official U.S. government information about the Global Positioning System (GPS) and related topics, for the article Space Segment,

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What is DGPS?

A system to provide additional correction factors to improve position accuracy.

From wp2ahg:

"Differential" GPS improves position accuracy over standard GPS from 15 meters to 10cm (best case).

From GPS.gov:

Global Differential GPS (GDGPS) is a high accuracy GPS augmentation system developed by the NASA Jet Propulsion Laboratory (JPL) to support the real-time positioning, timing, and determination requirements of NASA science missions.

From NASA Jet Propulsion Laboratory site, the article The Global Differential GPS (GDGPS) System. GDGPS has been providing high reliability position, navigation, and timing data services to industry and government operations since 2000.

For basic info on DGPS, please see Wikipedia's article Differential GPS.

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