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Encyclopedia > Satellite navigation system

Satellite navigation systems allow small electronic devices to determine their location (Longitude, Latitude, and Altitude) in within a few metres using time signals transmitted along a line of sight by radio from satellites. Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments. The Global Positioning System is the only fully functional satellite navigation system as of 2006. Wikipedia does not have an article with this exact name. ... The Global Navigation Satellite System (GNSS) systems. ... The field of electronics comprises the study and use of systems that operate by controlling the flow of electrons (or other charge carriers) in devices such as thermionic valves (vacuum tubes) and semiconductors. ... Longitude, sometimes denoted by the Greek letter λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. ... Latitude, usually denoted symbolically by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ... Altitude is the elevation of an object from a known level or datum. ... The metre, or meter (U.S.), is a measure of length. ... A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... When viewing a scene, as in optics, photography, or even hunting, the line of sight is the straight line between the observer and the target. ... MILSTAR:A communication satellite A satellite is any object that orbits another object (which is known as its primary). ... GPS redirects here. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ...

Contents

History and theory

Early predecessors were the ground based LORAN and Omega systems, which used terrestrial longwave radio transmitters instead of satellites. These systems broadcast a radio pulse from a known "master" location, followed by repeated pulses from a number of "slave" stations. The delay between the reception and sending of the signal at the slaves was carefully controlled, allowing the receivers to compare the delay between reception and the delay between sending. From this the distance to each of the slaves could be determined, providing a fix. LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from three or more stations to determine the position of a ship or aircraft. ... Omega is the name for the first truly global radionavigation system for aircraft operated by the United States of America in cooperation with six partner nations. ... The Longwave radio broadcasting band is the range of frequencies between 148. ... In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ... A position fix or simply a fix is a term used in position fixing in navigation to describe a position derived from measuring external reference points. ...


The first satellite navigation system was Transit, a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect: the satellites traveled on well-known paths and broadcast their signals on a well known frequency. The received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position. Operational Transit satellite The TRANSIT system, also known as NAVSAT (for Navy Navigation Satellite System), was the first satellite navigation system to be used operationally. ... The 1960s decade refers to the years from January 1, 1960 to December 31, 1969, inclusive. ... A source of waves moving to the left. ... Sine waves of various frequencies; the bottom waves have higher frequencies than those above. ...


Part of an orbiting satellite's broadcast included its precise orbital data. In order to ensure accuracy, the US Naval Observatory (USNO) continuously observed precisely the orbits of these satellites. As a satellite's orbit deviated, the USNO would send the updated information to the satellite. Subsequent broadcasts from an updated satellite would contain the most recent accurate information about its orbit. Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ...


Modern systems are more direct. The satellite broadcasts a signal that contains the position of the satellite and the precise time the signal was transmitted. The position of the satellite is transmitted in a data message that is superimposed on a code that serves as a timing reference. The satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation. The receiver compares the time of broadcast encoded in the transmission with the time of reception measured by an internal clock, thereby measuring the time-of-flight to the satellite. Several such measurements can be made at the same time to different satellites, allowing a continual fix to be generated in real time. Atomic clock Chip-Scale Atomic Clock Unveiled by NIST An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. ...


Each distance measurement, regardless of the system being used, places the receiver on a spherical shell at the measured distance from the broadcaster. By taking several such measurements and then looking for a point where they meet, a fix is generated. However, in the case of fast-moving receivers, the position of the signal moves as signals are received from several satellites. In addition, the radio signals slow slightly as they pass through the ionosphere, and this slowing varies with the receiver's angle to the satellite, because that changes the distance through the ionosphere. The basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centered on four satellites. Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity. The Kalman filter is an efficient recursive filter which estimates the state of a dynamic system from a series of incomplete and noisy measurements. ...


Civil and military uses

The original motivation for satellite navigation was for military applications. Satellite navigation allows for hitherto impossible precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from mis-directed weapons. (See smart bomb). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war. BOLT-117 laser guided bomb Precision-guided munitions (smart munitions or smart bombs) are self-guiding weapons intended to maximize damage to the target while minimizing collateral damage. Because the damage effects of an explosive weapon scale as a power law with distance, quite modest improvements in accuracy (and hence... The fog of war is the lack of knowledge that occurs during a war. ...

Satellite navigation using a laptop and a GPS receiver
Enlarge
Satellite navigation using a laptop and a GPS receiver

In these ways, satellite navigation can be regarded as a force multiplier. In particular, the ability to reduce unintended casualties has particular advantages for wars being fought by democracies, where public relations is an important aspect of warfare. For these reasons, a satellite navigation system is an essential asset for any aspiring military power. Satellite navigation. ... Satellite navigation. ... A laptop computer or simply laptop (also notebook computer or notebook) is a small mobile personal computer, which usually weighs 2. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... A force multiplier is a military term referring to a factor that dramatically increases (hence multiplies) the combat effectiveness of a military force. ...


Satellite navigation systems have a wide variety of civilian uses:

Note that the ability to supply satellite navigation signals is also the ability to deny their availability. The operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires. Thus, as satellite navigation becomes an essential service, countries without their own satellite navigation systems effectively become client states of those which supply these services. Table of geography, hydrography, and navigation, from the 1728 Cyclopaedia. ... Synchronization is a problem in timekeeping which requires the coordination of events to operate a system in unison. ... Location-based services (LBS) are offered by some cell phone networks as a way to send custom advertising and other information to cell-phone subscribers based on their current location. ... To meet Wikipedias quality standards and make it easier to understand, this article or section may require cleanup. ... Surveyor at work with a leveling instrument. ... A geographic information system (GIS) is a system for creating, storing, analyzing and managing spatial data and associated attributes. ... Search and Rescue (acronym SAR) is an operation mounted by emergency services, often well-trained volunteers, to find someone believed to be in distress, lost, sick or injured either in a remote or difficult to access area, such as mountains, desert or forest (Wilderness search and rescue), or at sea... In telecommunication, an essential service (critical service) is a network-provided service feature in which a priority dial tone is furnished. ...


The same applies to the use of smart bombs: the operator of a satellite navigation system can effectively degrade the performance of smart bombs being used by other states using its satellite navigation system to that of gravity bombs, or even offset them from their targets in such a way as to render them useless. BOLT-117 laser guided bomb Precision-guided munitions (smart munitions or smart bombs) are self-guiding weapons intended to maximize damage to the target while minimizing collateral damage. Because the damage effects of an explosive weapon scale as a power law with distance, quite modest improvements in accuracy (and hence... A U.S. developed B-61 gravity bomb. ...


Current and proposed satellite navigation systems

Main Article: Global Navigation Satellite Systems (GNSS) The Global Navigation Satellite System (GNSS) systems. ...


GPS

The best known satellite navigation system is the United States' Global Positioning System (GPS), and as of 2006 the GPS is the only fully functional satellite navigation system. This consists of 24 to 27 satellites that orbit in six different planes. The exact number of satellites varies as satellites are replenished when older ones are retired. They orbit at an altitude of approximately 20,000 km with an inclination of 55 degrees. The satellites are tracked by a world-wide network of monitor stations. The tracking data is sent to a master control station that continuously updates position and clock estimates for each satellite. The updated data is then uplinked to the satellite via one of several ground antennas. GPS redirects here. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ...


GLONASS

The (former) USSR counterpart to GPS is called GLONASS and was used as a backup by some commercial GPS receivers. The GLONASS constellation, which is now Russian, is expected to become fully operational by 2010. There are plans to include Indian participation as well. GLONASS GLONASS (Russian ГЛОНАСС; ГЛОбальная НАвигационная Спутниковая Система; Globalnaya Navigatsionnaya Sputnikovaya Sistema. ... For the film, see 2010: The Year We Make Contact. ...


Galileo

The European Union and European Space Agency agreed on March 2002 to introduce their own alternative to GPS, called Galileo. At a cost of about £2.4 billion[1], the required satellites will be launched between 2006 and 2008 and the system will be working, under civilian control, from 2010 (Two years later than originally anticipated). The first satellite was actually launched on 28 December 2005. Galileo is expected to be compatible with the next-generation GPS system that will be operational by 2012. The receivers will be able to combine the signals from 30 Galileo and 28 GPS satellites to greatly increase the accuracy. The European Space Agency (ESA), established in 1975, is an inter-governmental organization dedicated to the exploration of space, currently with 17 member states. ... For album titles with the same name, see 2002 (album). ... The Galileo positioning system is a proposed satellite navigation system, to be built by the European Union (EU) as an alternative to GPS (which is controlled by the United States military) and the Russian GLONASS. The system should be operational by 2010, two years later than originally anticipated. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... 2008 (MMVIII) will be a leap year starting on Tuesday of the Gregorian calendar. ... For the film, see 2010: The Year We Make Contact. ... December 28 is the 362nd day of the year (363rd in leap years) in the Gregorian Calendar, with 3 days remaining. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... 2012 (MMXII) will be a leap year starting on Sunday of the Gregorian calendar. ...


Beidou

China has started to launch a series of satellites intended to form a system called the Beidou navigation system. The Beidou navigation system is a project by the Peoples Republic of China to develop an independent satellite navigation system. ...


DORIS

DORIS (Doppler Orbitography and Radio-positioning Integrated by Satellite), French precision system. [2]


Topics to be covered

GNSS reflectometry involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. It is also known as GPS reflectometry. ... LAAS Architecture The Local Area Augmentation System (LAAS) is an all-weather landing system based on real-time differential correction of the GPS signal. ... WAAS Operation The Wide Area Augmentation System (WAAS) is an extremely accurate navigation system developed for civil aviation by the Federal Aviation Administration (FAA) in conjunction with the United States Department of Transportation (DOT). ...

External links


Satellite navigation systems
United States Transit | United States GPS | GLONASS | European Union Galileo | Beidou
Related topics: EGNOS | WAAS | LAAS

  Results from FactBites:
 
China to build satellite navigation system (182 words)
Navigation services open to commercial customers will provide users with positioning accuracy within 10 meters (33 feet), velocity accuracy within 0.2 meters per second and timing accuracy within 50 nanoseconds, the report said.
It was also not clear how the Chinese system would rival the American global positioning satellite system or the EU's Galileo satellite navigational system which is expected to be built with Chinese participation.
The system is expected to cover China and parts of neighbouring countries by 2008, before being expanded into a global network of satellites, it said.
NodeWorks - Encyclopedia: Satellite navigation system (1369 words)
Satellite navigation systems use radio time signals transmitted by satellites to enable mobile receivers on the ground to determine their exact location.
Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.
Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war.
  More results at FactBites »

 
 

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