Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. GPS satelliteEven fixed systems may use GPS, in order to get precise time. This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.

Discover great deals on the many hard to find and one of a kind items available only on ebay!

GPS

The Global Positioning System, usually called GPS (the US military refers to it as NAVSTAR GPS - Navigation Signal Timing and Ranging Global Positioning System), is the only operational satellite navigation system. more...

HomeHome
ComicsComics
ComputersComputers
ElectronicsElectronics
BlackberryBlackberry
BluetoothBluetooth
DVD PlayerDVD Player
GPSGPS
iPodiPod
Metal DetectorMetal Detector
mp3 Playermp3 Player
MoviesMovies
TelevisionTelevision
ToysToys
Video GamesVideo Games


For a list of other proposed and partially developed systems, including Russia's RONASS and Europe's Galileo, see satellite navigation system.

Satellite Navigation Systems can be used for determining one's precise location and providing a highly accurate time reference almost anywhere on Earth or in Earth orbit. The accuracy of the GPS signal itself is about 5 meters (16 ft) as of 2005 and has steadily improved over the last 15 years. Using differential GPS and other error-correcting techniques, the accuracy can be improved to about 1 cm (.4 in) over short distances.

The GPS system was designed by and is controlled by the United States Department of Defense and can be used by anyone, free of charge. The GPS system is divided into three segments: space, control and user. The space segment comprises the GPS satellite constellation of at least 24 satellites in an intermediate circular orbit (ICO) . The control segment comprises ground stations around the world that are responsible for monitoring the flight paths of the GPS satellites, synchronizing the satellites' onboard atomic clocks, and uploading data for transmission by the satellites. The user segment consists of GPS receivers used for both military and civilian applications. A GPS receiver decodes time signal transmissions from multiple satellites and calculates its position by trilateration.

Daily management of the GPS satellite constellation is conducted by the 2d Space Operations Squadron at Schriever Air Force Base. The cost of maintaining the system is approximately US$400 million per year, including the replacement of aging satellites. The first GPS satellite was launched in February 1978, and the most recent launch was in September 2005. The oldest GPS satellite still in operation was launched in February 1989.

Technical description

The system consists of a constellation of at least 24 satellites in 6 orbital planes. The GPS satellites were initially manufactured by Rockwell and now manufactured by Lockheed Martin. The first was launched in February 1978, and the most recent was launched September 25, 2005. Each satellite circles the Earth twice every day at an altitude of 20,200 kilometres (12,600 miles). The satellites carry atomic clocks and constantly broadcast the precise time according to their own clock, along with administrative information including the orbital elements of their own motion, as determined by a set of ground-based observatories.

The receiver does not need a precise clock, but does need a clock with good short-term stability and the ability to receive signals from four satellites in order to determine its own latitude, longitude, elevation, and the precise time. The receiver computes the distance to each of the four satellites from the difference between local time and the time the satellite signals were sent (this distance is called a pseudorange). It then decodes the satellites’ locations from their radio signals and an internal database. The receiver should now be located at the intersection of four spheres, one around each satellite, with a radius equal to the time delay between the satellite and the receiver multiplied by the speed of the radio signals. Because the receiver does not have a very precise clock it cannot compute the time delays. However, it can measure with high precision the differences between the times when the various messages were received and hence use multilateration to accurately locate itself. This yields 3 hyperboloids of revolution of two sheets, whose intersection point gives the precise location of the receiver. This is why at least four satellites are needed: fewer than 4 satellites yield 2 hyperboloids, whose intersection is a curve; it is impossible to know where the receiver is located along the curve without supplemental information, such as elevation. If elevation information is already known, only signals from three satellites are needed (the point is then defined as the intersection of two hyperboloids and an ellipsoid representing the Earth at this altitude).

Read more at Wikipedia.org


[List your site here Free!]

Garmin Rino 700 Gps Navigator Handheld Communicator Two-way Radio 010-01958-20Garmin Rino 700 Gps Navigator Handheld Communicator Two-way Radio 010-01958-20 $349.99 Garmin Nuvi 3597Lm 5" Gps Navigator (Pps001915)Garmin Nuvi 3597Lm 5" Gps Navigator (Pps001915) $109.95
Truck Vehicle Car Portable 7" Gps Navigation Navigator Sat Nav 8Gb Us Canada MapTruck Vehicle Car Portable 7" Gps Navigation Navigator Sat Nav 8Gb Us Canada Map $46.35 Garmin Gpsmap 78 Worldwide Floating Gps Handheld Watersports Marine 010-00864-00Garmin Gpsmap 78 Worldwide Floating Gps Handheld Watersports Marine 010-00864-00 $299.99
Garmin Gxm 53 SiriusXm Satellite Weather/Audio Receiver 010-01734-00Garmin Gxm 53 SiriusXm Satellite Weather/Audio Receiver 010-01734-00 $799.99 Lowrance Elite-9 Ti Combo with Med/High/DownScan Hdi Tm Transducer 000-13273-001Lowrance Elite-9 Ti Combo with Med/High/DownScan Hdi Tm Transducer 000-13273-001 $899.00
Garmin Gpsmap 7607xsv 7" Multi-touch Chartplotter/Sonar Combo 010-01379-03Garmin Gpsmap 7607xsv 7" Multi-touch Chartplotter/Sonar Combo 010-01379-03 $1,499.99 Humminbird Helix 7 Chirp Di Gps G2N Combo 410330-1Humminbird Helix 7 Chirp Di Gps G2N Combo 410330-1 $599.99
Garmin Gpsmap 64s Gps & Glonass Bluetooth or Ant+ 3-axis Handheld 010-01199-10Garmin Gpsmap 64s Gps & Glonass Bluetooth or Ant+ 3-axis Handheld 010-01199-10 $299.99 Garmin eTrex 30x 010-01508-10 Handheld NavigatorGarmin eTrex 30x 010-01508-10 Handheld Navigator $228.59
Garmin Panoptix Ps21 LiveVu Forward Transducer w/ Real-time Images 010-01588-00Garmin Panoptix Ps21 LiveVu Forward Transducer w/ Real-time Images 010-01588-00 $799.99 Garmin Gps 19x Nmea 2000 Compatible 32 Channels Antenna/Receiver 010-01010-10Garmin Gps 19x Nmea 2000 Compatible 32 Channels Antenna/Receiver 010-01010-10 $249.99
New Magellan RoadMate 9416T-Lm Gps Navigator with Free Lifetime Maps - SealedNew Magellan RoadMate 9416T-Lm Gps Navigator with Free Lifetime Maps - Sealed $89.59 Lowrance Endura Sierra Handheld /000-0125-40Lowrance Endura Sierra Handheld /000-0125-40 $499.99
Garmin nüvi 2557Lmt Automotive Mountable - Lifetime Maps - Mount IncludedGarmin nüvi 2557Lmt Automotive Mountable - Lifetime Maps - Mount Included $99.95 Trending at $116.98 Garmin Gpsmap 742 Touchscreen Chartplotter - No Sonar 010-01738-01Garmin Gpsmap 742 Touchscreen Chartplotter - No Sonar 010-01738-01 $899.99
Garmin Vivoactive Vivo Active 3 Gps Watch Silver 010-01769-01 BluetoothGarmin Vivoactive Vivo Active 3 Gps Watch Silver 010-01769-01 Bluetooth $243.98 Trending at $259.48 Garmin Nuvi 260 Gps Bundle Lifetime Maps Carrying Case 8Gb microSdhc Card Garmin Nuvi 260 Gps Bundle Lifetime Maps Carrying Case 8Gb microSdhc Card  $14.99
Garmin nuvi 260 Automotive Mountable Gps ReceiverGarmin nuvi 260 Automotive Mountable Gps Receiver $65.00 Garmin Gt30-Tm and Gt8Hw-Ih Transducer Shallow Water Combo Bundle 010-12763-00Garmin Gt30-Tm and Gt8Hw-Ih Transducer Shallow Water Combo Bundle 010-12763-00 $299.99
Garmin Gpsmap 64st Full-featured Handheld Gps Wireless Connectivity 010-01199-22Garmin Gpsmap 64st Full-featured Handheld Gps Wireless Connectivity 010-01199-22 $349.99 Garmin Oregon 650t Dual Battery System Handheld Gps Glonass 3-axis 010-01066-30Garmin Oregon 650t Dual Battery System Handheld Gps Glonass 3-axis 010-01066-30 $549.99
New Humminbird Helix 9x Si/gps Us & International 409950-1mNew Humminbird Helix 9x Si/gps Us & International 409950-1m $821.76 Garmin Gpsmap 276Cx All-Terrain Handheld Worldwide Basemap Gps 010-01607-01Garmin Gpsmap 276Cx All-Terrain Handheld Worldwide Basemap Gps 010-01607-01 $799.99
Garmin Oregon 600t Dual Battery Handheld Gps Glonass 3axis Compass 010-01066-10Garmin Oregon 600t Dual Battery Handheld Gps Glonass 3axis Compass 010-01066-10 $479.99 Garmin Gsd 25 Premium Fishfinding Capabilities Sounder Module 010-01159-00Garmin Gsd 25 Premium Fishfinding Capabilities Sounder Module 010-01159-00 $899.99
Garmin Gnx 130 10" Inverted Monochrome Marine Instrument Display 010-01396-00Garmin Gnx 130 10" Inverted Monochrome Marine Instrument Display 010-01396-00 $1,499.99 Garmin Nuvi 200 Gps UnitGarmin Nuvi 200 Gps Unit $20.00
Seat Portable Navigon Skoda Citigo Move Fun Seat Mi Sat Nav Navigation SatelliteSeat Portable Navigon Skoda Citigo Move Fun Seat Mi Sat Nav Navigation Satellite $267.22 Garmin Gpsmap 78s Gps Handheld Expandable Memory 3-axis Compass 010-00864-01Garmin Gpsmap 78s Gps Handheld Expandable Memory 3-axis Compass 010-00864-01 $399.99
Garmin Reactor 40 9 Axis Steer-By-Wire Autopilot for Viking Viper 010-00705-88Garmin Reactor 40 9 Axis Steer-By-Wire Autopilot for Viking Viper 010-00705-88 $6,799.99 Magellan RoadMate 700 3-Inch Display Portable Gps Navigator - Tested -ExcellentMagellan RoadMate 700 3-Inch Display Portable Gps Navigator - Tested -Excellent $24.99
Garmin Oregon 650 Handheld Gps w/ 8mp Camera Dual Battery 010-01066-20 AltimeterGarmin Oregon 650 Handheld Gps w/ 8mp Camera Dual Battery 010-01066-20 Altimeter $479.99 Garmin dēzl 770Lmthd Gps ReceiverGarmin dēzl 770Lmthd Gps Receiver $222.50
Garmin nuvi 255W +Free Shipping & Warranty!Garmin nuvi 255W +Free Shipping & Warranty! $25.82 Garmin Gxn 120 7" Segmented Lcd Large Format Instrument Display 010-01395-00Garmin Gxn 120 7" Segmented Lcd Large Format Instrument Display 010-01395-00 $899.99
Gps TomTom Xxl 310 with accessoriesGps TomTom Xxl 310 with accessories $30.00 Garmin R109Lh Thru-hull Dual Frequency External Chirp Transducer 010-11642-20Garmin R109Lh Thru-hull Dual Frequency External Chirp Transducer 010-11642-20 $2,696.43
Garmin Rino 750 Handheld Radio and Gps 5 W Frs/Gmrs 3" Touchscreen 010-01958-00Garmin Rino 750 Handheld Radio and Gps 5 W Frs/Gmrs 3" Touchscreen 010-01958-00 $549.99 Garmin Nuvi 265WtGarmin Nuvi 265Wt $13.50
Garmin nüvi 42Lm Automotive MountableGarmin nüvi 42Lm Automotive Mountable Garmin Nuvi 765 Gps Navigation Unit BundleGarmin Nuvi 765 Gps Navigation Unit Bundle $44.99
Garmin Montana 680t Gps Glonass Handheld w/ 8 mp Camera Topo Us 010-01534-11Garmin Montana 680t Gps Glonass Handheld w/ 8 mp Camera Topo Us 010-01534-11 $599.99 Garmin Gsd 24 Digital Black Box Network Sounder Module 010-00957-00Garmin Gsd 24 Digital Black Box Network Sounder Module 010-00957-00 $699.99
Nextar Satellite Navigation System M3-06 3.5" Color Touch ScreenNextar Satellite Navigation System M3-06 3.5" Color Touch Screen $24.99 Garmin Remote Input Device (Grid) 8000 Series Waterproof Plastic 010-01024-00Garmin Remote Input Device (Grid) 8000 Series Waterproof Plastic 010-01024-00 $399.99
GlobalSat Bu-353-S4 Usb Gps Receiver (Black)GlobalSat Bu-353-S4 Usb Gps Receiver (Black) $30.36 Garmin Gps 18x 5Hz Output Oem High-sensitivity Gps Sensor 010-00321-37Garmin Gps 18x 5Hz Output Oem High-sensitivity Gps Sensor 010-00321-37 $199.99
Garmin Rv 770Lmt-S Recreational Vehicle Gps w/ Live Traffic & Maps 010-01768-00Garmin Rv 770Lmt-S Recreational Vehicle Gps w/ Live Traffic & Maps 010-01768-00 $499.99
Click to see more GPS items at www.ebay.com
Prices current as of last update, 03/22/18 3:08pm.

Home Contact Resources Exchange Links ebay