What is Navigation

8/8/2019 What is Navigation

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Table of Contents:

What is Navigation? What is GPS? Elements of GPS. GPS Applications.

How GPS works? How is GPS used today? The future of GPS availability. The latest GPS Systems

What is Navigation?

Since prehistoric times, people have been trying to figure out a reliable way to

tell where they are and how to get to their destinationand back home again.Such knowledge often meant survival and economic power in society. Early

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cultures probably marked trails when they set out hunting for food. They laterbegan making maps and, by the Classical Age of Greece, developed the use oflatitude (your location on Earth measured north or south from the equator) andlongitude (your location on Earth measured east or west of a designated primemeridian) as a way of locating places. Today the prime meridian used

worldwide runs through the Greenwich Observatory in England.Sextant

Early mariners followed the coast closely to keep from getting lost. When theylearned to chart their course by following the stars, they could venture out intothe open seas. The ancient Phoenicians used the North Star to journey fromEgypt and Crete. According to Homer, the goddess Athena told Odysseus to"keep the Great Bear on his left during his travels from Calypsos Island.Unfortunately the stars are only visible at nightand only on clear nights.

Sometimes lighthouses provided a light to guide mariners at night and warnthem of nearby hazards.

The next major developments in navigation were the magnetic compass and thesextant. The needle of a compass always points to the magnetic North Pole, soit tells you your "heading, or the direction you're going. Mariner's maps in theAge of Exploration often depicted the headings between key ports and were

jealously guarded by their owners.

The sextant uses adjustable mirrors to measure the exact angle of the stars,

moon, and sun above the horizon. From these angles and an "almanac" of thepositions of the sun, moon and stars, you can determine your latitude in clearweather, day or night. Sailors, however, were still unable to determine theirlongitude. When you look at very old maps, you sometimes find that thelatitudes of the coastlines are accurate, but the longitudes are off by hundreds ofmiles. This was such a serious problem that in the 17th century the Britishgovernment formed a special Board of Longitude consisting of well-knownscientists. This group offered 20,000 British pounds, equal today to about$32,000 to anybody who could find a way to determine a ships longitudewithin 30 nautical miles.

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The offer paid off. The answer lay in knowing what time it is when you makeyour sextant measurements. For example, say your Greenwich almanac predictsthat the sun is highest at noon. Your shipboard clock, synchronized toGreenwich time when you left port, says it's 2 p.m. when your sextant measuresthat event. Then you must be the equivalent of two hours west of Greenwich.

In 1761 a cabinetmaker named John Harrison developed a shipboard timepiececalled a chronometer, which lost or gained only about one second a dayincredibly accurate for the time. For the next two centuries, sextants andchronometers were used in combination to provide latitudes and longitudes.

In the early 20th century several radio-based navigation systems weredeveloped and used widely during World War II. Both allied and enemy shipsand airplanes used ground-based radio-navigation systems as the technologyadvanced.

A few ground-based radio-navigation systems are still in use today. Onedrawback of using radio waves generated on the ground is that you have onlytwo choices:a system that is very accurate but doesnt cover a wide area; ora system that covers a wide area but is not very accurate

High-frequency radio waves (like cell phones) can provide accurate positionlocation but can only be picked up in a small, localized area. Lower frequencyradio waves (like FM radio) can cover a larger area, but are not a good

yardstick to tell you exactly where you are.

Scientists, therefore, decided that the only way to provide accurate coverage forthe entire world was to place high-frequency radio transmitters in space. Atransmitter high above Earth would broadcast a high-frequency radio wave witha special coded signal that could cover a large area and still reach Earth far

below at a useful power level. This is one of the main principles behind theGPS system. It brings together 2,000 years of advances in navigation by

providing precisely located "lighthouses in space" that are all synchronized to acommon time standard.

The GPS system can tell you your location anywhere on or above Earth towithin about 20 to 30 feet. Even greater accuracy, usually within less than threefeet, can be obtained with "differential corrections" calculated by a special GPSreceiver at a known fixed location.

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What is GPS?

GPSthe Most Precise Navigation System Ever Invented

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The Global Positioning System, or GPS, can show you your exact position onEarth any time, anywhere, in any weather. The system consists of aconstellation of 24 satellites (with about 6 "spares") that orbit 11,000 nauticalmiles above Earths surface and continuously send signals to ground stationsthat monitor and control GPS operations.

GPS satellite signals can also be detected by GPS receivers, which calculatetheir locations anywhere on Earth within less than a meter by determiningdistances from at least three GPS satellites. No other navigation system has ever

been so global or so accurate.

First launched in 1978, the development of a global navigation system datesback to the 1960s when The Aerospace Corporation was a principal participantin the conception and development of GPS, a technology that has significantly

enhanced the capabilities of our nations military and continues to find newuses and applications in daily life. Weve helped build GPS into one ofhistorys most exciting and revolutionary technologies and continue to

participate in its ongoing operation and enhancement.

Elements of GPS

GPS has three parts: the space segment, the user segment, and the controlsegment. The space segment consists of a constellation of 24 satellites (andabout six "spares"), each in its own orbit 11,000 nautical miles above Earth.The user segment consists of receivers, which you can hold in your hand ormount in a vehicle, like your car. The control segment consists of groundstations (six of them, located around the world) that make sure the satellites areworking properly. The master control station at Schriever Air Force Base, nearColorado Springs, Colorado, runs the system.

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To help you understand GPS lets discuss the three parts of the systemthesatellites, the receivers, and the ground stationsand then look more closely athow GPS works.

o A Constellation of Satellites:

An orbit is one trip in space around Earth. GPS satellites each take 12 hours toorbit Earth. Each satellite is equipped with an atomic clock so accurate that itkeeps time to within three nanosecondsthats 0.000000003, or three-

billionths, of a secondto let it broadcast signals that are synchronized withthose from other satellites.

The signal travels to the ground at the speed of light. Even at this speed, thesignal takes a measurable amount of time to reach the receiver. The difference

between the time when the signal is received and the time when it was sent,multiplied by the speed of light, enables the receiver to calculate the distance tothe satellite. To make this measurement as accurate as possible, the GPSnavigation signals are specially designed to make it easy for GPS receivers tomeasure the time of arrival and to allow all the satellites to operate on the samefrequency without interfering with each other. To calculate its precise latitude,longitude, and altitude, the receiver measures the distance to four separate GPSsatellites. By using four satellites, the receiver calculates both its position andthe time and doesn't need an expensive atomic clock like those on the satellites.

o

Receivers:

GPS receivers can be carried in your hand or be installed on aircraft, ships,tanks, submarines, cars, and trucks. These receivers detect, decode, and processGPS satellite signals. More than 100 different receiver models are already inuse. The typical hand-held receiver is about the size of a cellular telephone, andthe newer models are even smaller and fit in a wristwatch or a Personal DataAssistant. The commercial hand-held units distributed to U.S. armed forces

personnel during the Persian Gulf War weighed only 28 ounces (less than two pounds). Since then, basic receiver functions have been miniaturized onto

integrated circuits that weigh about one ounce.

o Ground Stations:

The GPS control segment consists of several ground stations located around theworld.

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A master control station at Schriever Air Force Base in Colorado

Six unstaffed monitoring stations: Hawaii and Kwajalein in the PacificOcean; Diego Garcia in the Indian Ocean; Ascension Island in theAtlantic Ocean; Cape Canaveral, Florida and Colorado Springs,Colorado

Four large ground-antenna stations that send commands and data up tothe satellites and collect telemetry back from them.

The monitor stations track the navigation signals and send their data back to themaster control station. There, the controllers determine any adjustments orupdates to the navigation signals needed to maintain precise navigation andupdate the satellites via the ground antennas. To further improve systemaccuracy, in 2005, the master control station added data from six monitorstations operated by the National Geospatial-Intelligence Agency to the six GPSmonitor stations.

GPS Applications

GPS has a wide range of applications. All of them fall under five basiccategories:

Location

Navigation

Tracking

Mapping

Timing

Combining GPS with current and future computer mapping techniques wouldenable us to identify and manage our natural resources. Smart vehicle locationand GPS navigation systems are GPS systems that would help us find efficientroutes to our destinations save a substantial amount of money and reduce air

pollution to a large extent. Businesses would be able to manage their resourcesmore efficiently, thus reducing consumer costs. Traveling aboard ships andaircrafts will be safer in all weather conditions.

There are two 'public' Global Positioning Systems (GPS systems):

NAVSTAR

GLONASSThe NAVSTAR is a GPS device owned by the United States, it managed by the

NAVSTAR GPS Joint Program Office located at Los Angeles Air Force Base.The civilian point of contact for the NAVSTAR system is the United StatesCoast Guard's Navigation Center (NAVCEN). The GLONASS system is owned

by the Russian Federation. The point of contact for GLONASS information is

the Russian Space Forces' Coordinational Scientific Information Center (CSIC).

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How GPS Works?

The principle behind GPS is the measurement of distance (or range) between

the satellites and the receiver. The satellites tell us exactly where they are intheir orbits by broadcasting data the receiver uses to compute their positions. Itworks something like this: If we know our exact distance from a satellite inspace, we know we are somewhere on the surface of an imaginary sphere with aradius equal to the distance to the satellite radius. If we know our exact distancefrom two satellites, we know that we are located somewhere on the line wherethe two spheres intersect. And, if we take a third and a fourth measurementfrom two more satellites, we can find our location. The GPS receiver processesthe satellite range measurements and produces its position.

GPS uses a system of coordinates called WGS 84, which stands for WorldGeodetic System 1984. It allows surveyors all around the world to producemaps like the ones you see in school, all with a common reference frame for thelines of latitude and longitude that locate places and things. Likewise, GPS uses

time from the United States Naval Observatory in Washington, D.C., tosynchronize all the timing elements of the GPS system, much like Harrison'schronometer was synchronized to the time at Greenwich.

Now you should have a fairly clear picture of the GPS system. You know that itconsists of satellites whose paths are monitored by ground stations. Eachsatellite generates radio signals that allow a receiver to estimate the satellitelocation and distance between the satellite and the receiver. The receiver usesthe measurements to calculate where on or above Earth the user is located.

What's the signal?

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GPS satellites transmit two low power radio signals, designated L1 and L2.Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. Thesignals travel by line of sight, meaning they will pass through clouds, glass and

plastic but will not go through most solid objects such as buildings andmountains.

A GPS signal contains three different bits of information - a pseudorandomcode, ephemeris data and almanac data. The pseudorandom code is simply anI.D. code that identifies which satellite is transmitting information. You canview this number on your Garmin GPS unit's satellite page, as it identifieswhich satellites it's receiving.

Ephemeris data, which is constantly transmitted by each satellite, contains

important information about the status of the satellite (healthy or unhealthy),current date and time. This part of the signal is essential for determining aposition.

The almanac data tells the GPS receiver where each GPS satellite shouldbe at any time throughout the day. Each satellite transmits almanac datashowing the orbital information for that satellite and for every othersatellite in the system.

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How GPS Is Used Today?

o Military Uses for GPSAlthough the GPS system was completed only in 1994, it has already

proved to be a valuable aid to U.S. military forces. Picture the desert,with its wide, featureless expanses of sand. The terrain looks much thesame for miles. Without a reliable navigation system, U.S. forces couldnot have performed the maneuvers of Operation Desert Storm. WithGPS the soldiers were able to go places and maneuver in sandstorms orat night when even the Iraqi troops who lived there couldnt. More than1,000 portable commercial receivers were initially purchased for theiruse. The demand was so great that before the end of the conflict, more

than 9,000 commercial receivers were in use in the Gulf region. Theywere carried by soldiers on the ground and were attached to vehicles,helicopters, and aircraft instrument panels. GPS receivers were used inseveral aircraft, including F-16 fighters, KC-135 aerial tankers, and B-52

bombers. Navy ships used them for rendezvous, minesweeping, andaircraft operations.GPS has become important for nearly all military operations andweapons systems. It is also used on satellites to obtain highly accurateorbit data and to control spacecraft orientation.

o GPS in Everyday Life

The GPS system was developed to meet military needs, but new ways touse its capabilities in everyday life are continually being found. As youhave read, the system has been used in aircraft and ships, but there aremany other ways to benefit from GPS. Well mention just a few to giveyou an idea of its many uses.GPS is helping to save lives and property across the nation. In 2002, itenabled rescuers to drill a shaft to free trapped miners in Somerset PA.Many police, fire, and emergency medical-service units use GPSreceivers to determine the police car, fire truck, or ambulance nearest toan emergency, enabling the quickest possible response in life-or-deathsituations. GPS-equipped aircraft can quickly plot the perimeter of aforest fire so fire supervisors can produce updated maps in the field andsend firefighters safely to key hot spots.

Mapping, construction, and surveying companies use GPS extensively.During construction of the tunnel under the English Channel, British andFrench crews started digging from opposite ends: one from Dover,England, and one from Calais, France. They relied on GPS receiversoutside the tunnel to check their positions along the way and to makesure they met exactly in the middle. Otherwise, the tunnel might have

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been crooked. GPS allows mine operators to navigate mining equipmentsafely, even when visibility is obscured.

Remember the example of the car with a video display in the dashboard?

Vehicle tracking is one of the fastest-growing GPS applications today.GPS-equipped fleet vehicles, public transportation systems, deliverytrucks, and courier services use receivers to monitor their locations at alltimes for both efficiency and driver safety.

Automobile manufacturers are offering moving-map displays guided byGPS receivers as an option on new vehicles. The displays can beremoved and taken into a home to plan a trip. Several major rental carcompanies have GPS-equipped vehicles that give directions to drivers ondisplay screens and through synthesized voice instructions. Imagine

never again getting lost on vacation, no matter where you are.

GPS-equipped balloons monitor holes in the ozone layer over the PolarRegions as well as air quality across the nation. Buoys tracking major oilspills transmit data using GPS to guide cleanup operations.Archaeologists, biologists, and explorers are using the system to locateancient ruins, migrating animal herds, and endangered species such asmanatees, snow leopards, and giant pandas.

The future of GPS is as unlimited as your imagination. New applications

will continue to be created as technology evolves. GPS satellites, likestars in the sky, will be guiding us well into the 21st century.

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GPS Timeline

1960April 13 the first navigation satellite TRANSIT IB is launched for use by theU.S. Navy to accurately locate ballistic missile submarines and ships.

May 15 Drs. Ivan Getting and Shep Arikin of Raytheon propose a radio-navigation system called MOSAIC (Mobile System for Accurate ICBMControl) to the U.S. Air Force.

June 3 The Aerospace Corporation is established "to aid the United States AirForce in applying the full resources of modern science and technology to the

problem of achieving those continuing advances in ballistic missiles and

military space systems which are basic to national security." Dr. Ivan Gettingbecomes the company's first president.

1963Project 57 begins at The Aerospace Corporation. The study seeks to clarifyareas where space systems could be used for military applications. According toDr. Ivan Getting, it was "in this study that the concept for GPS was born."

Under the direction of the Air Force, the Project 57 study becomes Project621B, and Aerospace is asked to continue its work on determining navigationcoordinates from satellite signals. Dr. Brad Parkinson notes that Project 621B"had many of the attributes that you now see in GPS. It has probably never beengiven its due credit."

1964-1966Aerospace scientists and engineers conduct a series of satellite navigationstudies within the companys Systems Planning Division. These studies arriveat the operational concept for GPS as we know it today.

1972November Air Force Col. Dr. Brad Parkinson is assigned by Gen. Ken Schultzto manage the 621B program. Parkinson's recognition that a synthesis of threecompeting satellite navigation proposals was needed marked the beginning ofthe first real progress toward the eventual approval of GPS by the DefenseDepartment.

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1973April U.S. Navy TIMATION system and the Air Force System 621B 3dnavigation system combine in an effort to develop a Defense NavigationSatellite System, which would later become NAVSTAR or GPS.

1974August 17 the deputy secretary of defense suggests a program based on theGPS concept be established, marking the start of the conception-validation

phase of the program.

1978February 22 after an initial launch failure, the first the GPS Block I satellites islaunched. Block I comprised 10 developmental satellites launched from 1978 through

1989.

1983May 20 The Air Force signs a $1.2 billion contract for the production of 28GPS Block II satellites with Rockwell Space Systems.

September a Korean civilian airliner is shot down by Russian fighters afteraccidentally intruding into Soviet air space. To prevent any such tragedy fromhappening again, President Ronald Reagan declassifies NAVSTAR; GPS

becomes available to civilians.

1985October 9 the last of the Block 1 satellites is launched.

1989February 14 the first of the GPS Block II production satellites is launched.From 1989 to 1997, 28 production satellites are launched; the last 19 satellitesin the series are updated versions, called Block IIA.

1990December NAVSTAR GPS becomes operational.

1991The Persian Gulf War enables American military forces to validate theusefulness of GPS in combat situations. Although not fully operational, GPSallows the military to obtain accurate coordinates in the featureless Iraqi desertand to achieve a quick victory.

1992

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The Aerospace Corporation, as part of the GPS team, receives the CollierTrophy, the nation's most prestigious aeronautical award for the work it hasdone developing GPS.

1994January 17 the last of the Block IIA satellites is launched, completing the GPSconstellation.

February 17 The Federal Aviation Administration announces that GPS isoperational an integrated as a part of the U.S. air traffic control system.

March 9 The Air Force announces the completion of the 24 Block II GPSsatellite constellation.

1995April 27 Air Force Space Command declares the Block II NAVSTAR GPSconstellation fully operational.

1996March 29 The National Security Councils Office of Science and TechnologyPolicy detail a comprehensive national policy for the use and management ofGPS.

1997

January 17 The Delta rocket carrying the first of the GPS Block IIR satellitesexplodes after liftoff.

2001-2003Military battles in Afghanistan following the September 11 attacks and duringOperation Iraqi Freedom demonstrate the precision of GPS in military conflict.

2003

October 11 Dr. Ivan Getting dies at the age of 91 at his home in Coronado,California.

2004March Drs. Ivan Getting and Brad Parkinson are awarded the Charles StarkDraper Prize by the National Academy of Engineering.

March 18 GPS satellite 2R-11 is dedicated to the late Dr. Ivan A. Getting, whoenvisioned these lighthouses in the sky serving all mankind.A plaqueinscribed with his words is attached to the satellite.

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May Drs. Ivan Getting and Brad Parkinson are inducted into the NationalInventors Hall of Fame.

2005

The first of GPS Block IIF satellites are scheduled to launch.

The future of GPS availability

GPS system close to breakdown: Network of satellites could begin to fail asearly as 2010 read the headline of the Online-Guardian from May 19th, 2009.

Similar news can be found in most mainstream media sources from the last twomonths. As usual, however, there is a different story behind it, and this story isfar less scary than the catchy headlines suggest. To the credit of more seriousmagazines, most articles have made the right statements at some point; butunfortunately, without explaining what it really means, the headline leaves alasting impression with the reader. This originated with a published report bythe respected U.S. Government Accountability Office (GAO) called GlobalPositioning System: Significant Challenges in Sustaining and UpgradingWidely Used Capabilities. These reports can all be downloaded (see thereferences section for the URL).

Summary of the GAO Report

The three main points of the report [3] are:

1. In recent years, the Air Force has struggled to successfully buildGPS satellites within cost and schedule goals the current IIF satellite

program has overrun its original cost estimate by about $870 million and thelaunch of its first satellite has been delayed to November 2009 almost 3years late.

2. Of particular concern is leadership for GPS acquisition, as GAO andother studies have found the lack of a single point of authority for space

programs and frequent turnover in program managers have hamperedrequirements setting, funding stability, and resource allocation.

3. If the Air Force does not meet its scheduled goals for developmentof GPS IIIA satellites, there will be an increased likelihood that in 2010, asold satellites begin to fail, the overall GPS constellation will fall below thenumber of satellites required to provide the level of GPS service that the U.S.

government commits to.

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GAOs recommendation is for the Secretary of Defense to [3] appoint a singleauthority to oversee the development of GPS, including space, ground control,and user equipment assets, to ensure these assets are synchronized and wellexecuted, and potential disruptions are minimized.

Based on a worst-case scenario of predicted satellite failures, the authorpublished a graph within the report. Most articles refer to this graph, whichdepicts the loss of aging satellites over the next few years:

Essentially, the graph depicts that the probability of havingat least 24 satellites in orbit will fall below the U.S.governments promise of 95%. This could occur between2010 and 2014, and it could reach a low point of 80%.

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What does it mean?

First, this does not mean that it will occur. These are

purely probabilistic assumptions of a worst-case scenario.There are many ifs and coulds involved, and most arerelated to the probability of acquiring new satellites ontime, assuming that the old satellites will inevitably fail.However, it is GAOs duty to give early warnings to thegovernment to avoid potential damage. The probabilitythat this will actually happen is not very high; do not beconfused by the numbers. Today there are 31 satellitesavailable for GPS positioning.

This graph is actually not the focus of their concern themain problem is lack of leadership and cost overruns, notthe technical problems that are being highlighted now.

The operational life of satellites depends mostly on solar-powered energy supplies. These devices tend to degradeover time until they are no longer able to maintain all sub-systems of the satellite. Shutting down select sub-systemswhen they are not needed can significantly prolong thelife-span of a satellite.

The media has focused on the spectacular aspects of thestory, producing news that attracts attention withoutexplaining the boring technical details. But why shouldanybody believe that the U.S. government will let this vitalmilitary system fail when the problem can be solved withmoney and man-power?

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The Latest GPS Systems

GPS systems are the newest in location technology thatcan help you find your way without getting lost, and theycan also locate your vehicle if it is stolen. These systemswork by using satellites that are orbiting the earth to findyour exact location and then find the way to get where youneed to go. GPS stands for global positioning satellite andat least three of the twenty four satellites that circle the

earth in orbit are needed to pinpoint exactly any givenlocation.

GPS systems come in hand held models and built insystems. Some cell phones, especially ones marketed forkids, come with a GPS system that will allow parents tolocate their child through the cell phone. GPS car systemscan be very simple or very complex, depending on themodel you choose and these systems use a CD or DVDwith very detailed map information, as well as the GPS

receiver. If your car is stolen and it has a GPS system,police can usually locate the missing vehicle withinminutes, which can lead to the apprehension of thethieves. Some GPS systems will give you verbal directions,and the more advanced systems can even upload trafficinformation so that you can avoid road construction andtraffic backups or accidents.

These systems can be very convenient and a great time

saver, especially for anyone who gets lost easily or a lot.The cost of the systems vary, depending on the model andfeatures you choose, and they can range from a couplehundred dollars for a basic system with a single car tothousands of dollars for businesses who have a lot ofbusiness vehicles, or a GPS system which is loaded withadditional features and a top of the line name.

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