11

Evolution of Military GPSEvolution of Military GPS

Deployment of Sputnik and its Doppler ShiftDeployment of Sputnik and its Doppler Shift Doppler Data and the Birth of the Transit Doppler Data and the Birth of the Transit

System and Timation SystemSystem and Timation System Early GPS Early GPS Today GPS Today GPS

Richard Stewart

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Sputnik: Learning From OurSputnik: Learning From OurRivalsRivals

In 1957, the Soviets successfully In 1957, the Soviets successfully launched Sputnik into space. It was launched Sputnik into space. It was the size of a basketball and weighed the size of a basketball and weighed about 180 pounds. about 180 pounds.

The Soviets’ success embarrassed the The Soviets’ success embarrassed the United States who thought they were United States who thought they were the world’s most advanced industrial the world’s most advanced industrial nation. As a result of their humiliation, nation. As a result of their humiliation, the country took an active role into the country took an active role into researching military precision. researching military precision.

The Department of Defenses primary The Department of Defenses primary purposes in developing a Global purposes in developing a Global Position System was to use it in Position System was to use it in precision weapon deliveryprecision weapon delivery

33

Sputnik: Learning From OurSputnik: Learning From OurRivalsRivals

Studying the Doppler Shift of the Sputnik, the Johns Hopkins Studying the Doppler Shift of the Sputnik, the Johns Hopkins Applied Physics Lab recognized a variance of the Sputnik signal Applied Physics Lab recognized a variance of the Sputnik signal in comparison of its position. As the fast-moving Sputnik in comparison of its position. As the fast-moving Sputnik approached, the scientists noted that signal frequency was approached, the scientists noted that signal frequency was higher than the transmitted frequency. They also observed that higher than the transmitted frequency. They also observed that the frequency lowered until the satellite reached its closet point the frequency lowered until the satellite reached its closet point of approach (CPA), when the observed frequency equaled the of approach (CPA), when the observed frequency equaled the transmitted frequency. The frequency decreased as Sputnik transmitted frequency. The frequency decreased as Sputnik moved farther away, although the rate of decrease slowed with moved farther away, although the rate of decrease slowed with increasing distance from the observers. This Doppler shift increasing distance from the observers. This Doppler shift phenomenon that the scientists observed was the same one you phenomenon that the scientists observed was the same one you experience when an express train rushes by you at a local experience when an express train rushes by you at a local station and you hear its roaring sound drop sharply in pitch. station and you hear its roaring sound drop sharply in pitch.

At the end of their experiments, the scientists reasoned that they At the end of their experiments, the scientists reasoned that they could accurately locate their position on earth by carefully could accurately locate their position on earth by carefully measuring the satellite's Doppler shift and knowing the satellite's measuring the satellite's Doppler shift and knowing the satellite's position in orbit at the exact instant of each measurement. position in orbit at the exact instant of each measurement.

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Doppler Data and the Birth of the Transit Doppler Data and the Birth of the Transit System and Timation SystemSystem and Timation System

Under the direction of Dr. Richard Kirschner, the John Under the direction of Dr. Richard Kirschner, the John Hopkins Applied Physics Laboratory created the Transit. Hopkins Applied Physics Laboratory created the Transit. Transit was conceived in the late 1950s and deployed in Transit was conceived in the late 1950s and deployed in the mid-1960sthe mid-1960s

Transit was the first operational satellite-based navigation Transit was the first operational satellite-based navigation system which included seven low-altitude (1075 km) polar-system which included seven low-altitude (1075 km) polar-orbiting satellitesorbiting satellites

In Transit In Transit 1. a satellite broadcasted radio signals 1. a satellite broadcasted radio signals 2.the ground stations tracked the satellite2.the ground stations tracked the satellite3. facilities updated satellite orbital parameters3. facilities updated satellite orbital parameters

The result- transit users determined their position on earth The result- transit users determined their position on earth by measuring the Doppler shift signals transmitted by the by measuring the Doppler shift signals transmitted by the satellitessatellites

55

TransitTransit Developed to provide accurate navigation data Developed to provide accurate navigation data

for Polaris missile submarines and other ships for Polaris missile submarines and other ships at the ocean surfaceat the ocean surface

The way it workedThe way it worked– Doppler-shifted signals enabled a determination Doppler-shifted signals enabled a determination

of the orbit using data recorded at one site of the orbit using data recorded at one site during a single pass of the satellite. So if a during a single pass of the satellite. So if a satellite’s orbit was known, a radio receiver’s satellite’s orbit was known, a radio receiver’s position could be determined from the same position could be determined from the same Doppler measurements.Doppler measurements.

– Unlike the Doppler data used to track the Unlike the Doppler data used to track the Sputnik satellite, Transit satellites could be Sputnik satellite, Transit satellites could be precisely determined by tracking them at widely precisely determined by tracking them at widely spaced fixed sites.spaced fixed sites.

A satellite had a 107 min. period of revolution-A satellite had a 107 min. period of revolution-under favorable conditions accuracy was under favorable conditions accuracy was between 35 and 100m.between 35 and 100m.

66

Positives and Negatives of TransitPositives and Negatives of Transit

PositivesPositives– Proof that a space system could offer excellent Proof that a space system could offer excellent

positioning reliabilitypositioning reliability– Was available to civilian users in 1967 including Was available to civilian users in 1967 including

commercial marine navigators and personal craftscommercial marine navigators and personal crafts– Created technologies Created technologies

NegativesNegatives– Large gaps in coverage Large gaps in coverage

unavailable coverage measuring up to several hoursunavailable coverage measuring up to several hours To compensate, users had to interpolate To compensate, users had to interpolate (to estimate a value of a function (to estimate a value of a function

between two known values) between two known values) their positions between passes. their positions between passes. Users had to compensate for their velocity Users had to compensate for their velocity Weather conditions could disrupt signalWeather conditions could disrupt signal

77

Negatives cont.Negatives cont.

– The process was slow and required long The process was slow and required long observation timeobservation time

– Only provided two-dimensional positioning Only provided two-dimensional positioning – Transit was not efficient for the more high Transit was not efficient for the more high

velocity technology (aircrafts, missiles, etc.) velocity technology (aircrafts, missiles, etc.) being developed by the militarybeing developed by the military

Nevertheless, the Transit system continued Nevertheless, the Transit system continued to be used until 1996 after about 33 years of to be used until 1996 after about 33 years of service.service.

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TimationTimation

Timation was a spaced-Timation was a spaced-based navigation system based navigation system technology program that technology program that was developed in 1964 by was developed in 1964 by the Navy.the Navy.

Advanced the Advanced the development of the development of the stability of clocks (time stability of clocks (time precision), time-transfer, precision), time-transfer, and two-dimensional and two-dimensional navigation.navigation.

1967- First Timation 1967- First Timation satellite launched satellite launched

99

Timation ModelsTimation Models

The first satellite used a very stable quartz-The first satellite used a very stable quartz-crystal oscillatorscrystal oscillators

Later models incorporated the first atomic Later models incorporated the first atomic frequency stabilityfrequency stability– Atomic clocks have better frequency stability Atomic clocks have better frequency stability

than earlier clocks=better prediction of satellite than earlier clocks=better prediction of satellite orbitsorbits

1010

Timation ContributionTimation Contribution

Development in the atomic clock for satellite Development in the atomic clock for satellite navigationnavigation

The last two Timation satellites were used as The last two Timation satellites were used as GPS prototypesGPS prototypes

Navigation Technology Satellite 1 (3rd satellite)

1111

System 621BSystem 621B

Around the same time the Navy was developing Around the same time the Navy was developing Timation, the Air Force worked with a design Timation, the Air Force worked with a design concept using a similar technology program called concept using a similar technology program called System 621B.System 621B.

Biggest Improvement- 3 dimensional navigation!!! Biggest Improvement- 3 dimensional navigation!!! (latitude, longitude, and altitude)(latitude, longitude, and altitude)

By 1972, the system was using a certain type of By 1972, the system was using a certain type of satellite ranging signal called pseudorandom noise satellite ranging signal called pseudorandom noise (PRN)(PRN)

1212

System 621BSystem 621B

System originated at the Aerospace System originated at the Aerospace Corporation in 1963 developed for precise Corporation in 1963 developed for precise positioning of aircraftspositioning of aircrafts

By Oct. 1963, System 621B was successful By Oct. 1963, System 621B was successful enough to get Air Force supporting and enough to get Air Force supporting and fundingfunding

Around 1972, ran a series or aircraft tests in Around 1972, ran a series or aircraft tests in New Mexico using a ground and air New Mexico using a ground and air transmitters to simulate satellites…result…transmitters to simulate satellites…result…

1313

White Sands Proving Ground in New White Sands Proving Ground in New MexicoMexico

Pseudorandom noise pinpointed Pseudorandom noise pinpointed the positions of aircrafts to within a the positions of aircrafts to within a hundredth of a mile= 16 meters hundredth of a mile= 16 meters

PRN technique had the capability to PRN technique had the capability to reject interference noise including reject interference noise including jamming or deliberate interference. jamming or deliberate interference. PRN techniques allow all satellites PRN techniques allow all satellites to transit on same frequency, to transit on same frequency, therefore a communication channel therefore a communication channel could be added permitting user to could be added permitting user to receiver data (satellite location and receiver data (satellite location and clock information.clock information.

1414

Military DivisionMilitary Division

By the late 1960s, the U.S. Navy, Air Force, and By the late 1960s, the U.S. Navy, Air Force, and Army worked independently on radio navigation Army worked independently on radio navigation systems that would provide all-weather, 24-hour systems that would provide all-weather, 24-hour coverage, and accuracies that would enhance the coverage, and accuracies that would enhance the military capabilities of their respective forces.military capabilities of their respective forces.

John Hopkins Applied Physics Laboratory-TransitJohn Hopkins Applied Physics Laboratory-Transit Naval Research Laboratory-Timation Naval Research Laboratory-Timation Army-SECOR (Sequential Correlation of Range)Army-SECOR (Sequential Correlation of Range)

1515

Military UnityMilitary Unity

1968-Department of Defense steps in creates a 1968-Department of Defense steps in creates a joint tri-service committee called the NAVSEG joint tri-service committee called the NAVSEG (Navigation Satellite Executive Group)(Navigation Satellite Executive Group)

What NAVSEG had to determine?What NAVSEG had to determine?– How many satellites?How many satellites?– What altitude?What altitude?– What would be the signal codesWhat would be the signal codes– What would be the modulation techniquesWhat would be the modulation techniques– CostCost

1616

Early GPSEarly GPS

September 1973, a system was developed September 1973, a system was developed combining early Navy and Air Force combining early Navy and Air Force programs called NAVSTAR GPSprograms called NAVSTAR GPS– System merged System 621B and Timation System merged System 621B and Timation

technologytechnology Satellites orbits were based on Timation but would Satellites orbits were based on Timation but would

have a higher altitude. have a higher altitude. Signal structure and frequencies were based on Signal structure and frequencies were based on

System 621BSystem 621B Satellites would use atomic clocks Satellites would use atomic clocks

1717

3-Phase Development of the 3-Phase Development of the NAVSTAR GPSNAVSTAR GPS

(1974-1979)- $100 million program(1974-1979)- $100 million program– First two NAVSTAR satellites were First two NAVSTAR satellites were

refurbished Timation satellites refurbished Timation satellites carrying the first atomic clocks ever carrying the first atomic clocks ever launched into spacelaunched into space

(1978-1985)- Rockwell International(1978-1985)- Rockwell International– Built a total of eleven Block I Built a total of eleven Block I

satellites launched on the Atlas-F satellites launched on the Atlas-F booster.booster.

– Design life was only 3 years but Design life was only 3 years but many last 10+ yearsmany last 10+ years

66thth Block I satellite carried a nuclear Block I satellite carried a nuclear explosion detection sensor which explosion detection sensor which was launched on April 36, 1980was launched on April 36, 1980

– Block I satellites were being tested Block I satellites were being tested for on aircraft, helicopter, ships, for on aircraft, helicopter, ships, trucks, jeeps, and even by men trucks, jeeps, and even by men using 25-pound backpacks.using 25-pound backpacks.

1818

22ndnd Stage of GPS Stage of GPS

Funding cut!!!- Secretary of Defense cut Funding cut!!!- Secretary of Defense cut program by 30% ($500 million)program by 30% ($500 million)

Result-Result-– Number of satellites were cut down: 24-18 (plus Number of satellites were cut down: 24-18 (plus

3 on-orbit spares)3 on-orbit spares)– Development of Block II satellites were droppedDevelopment of Block II satellites were dropped

Increased the interest in the program by Increased the interest in the program by stressing that GPS could increase bombing stressing that GPS could increase bombing accuracyaccuracy

1919

Block II SatellitesBlock II Satellites

With a renew interest by With a renew interest by the Secretary of Defense, the Secretary of Defense, Block II satellites were Block II satellites were developed and launched in developed and launched in Feb. 1989Feb. 1989

Operational by April Operational by April 1989/created Rockwell 1989/created Rockwell InternationalInternational– ImprovementsImprovements

Full selective availability/ Full selective availability/ advanced system securitiesadvanced system securities

Improved reliability and Improved reliability and survivabilitysurvivability

2020

33rdrd Phase Phase

Launch of the Block II/IIA/IIR and finally IIR Launch of the Block II/IIA/IIR and finally IIR combining up to 33 satellites (including spares) to combining up to 33 satellites (including spares) to consist of our new GPS. GPS today uses 24 consist of our new GPS. GPS today uses 24 satellites and numerous ground stationssatellites and numerous ground stations

LAND SEA AIR

Able to get quick accurate readings no matter the weather condition, time of day, or velocity

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BibliographyBibliography Steven R. StromSteven R. Strom Charting a Course Toward Global NavigationCharting a Course Toward Global Navigation

http://www.aero.org/publications/crosslink/summer2002/01.htmlhttp://www.aero.org/publications/crosslink/summer2002/01.html History of GPSHistory of GPS http://www.bugclub.org/beginners/history/gps.html http://www.bugclub.org/beginners/history/gps.html Mary BellisMary Bellis Global Positioning System - GPSGlobal Positioning System - GPS

http://inventors.about.com/library/inventors/blgps.htmhttp://inventors.about.com/library/inventors/blgps.htm Robert A. NelsonRobert A. Nelson The Global Positioning SystemThe Global Positioning System Via SatelliteVia Satellite, November , November

1999 http://www.aticourses.com/global_positioning_system.htm1999 http://www.aticourses.com/global_positioning_system.htm Sam Wormley’s DGPS Resources Sam Wormley’s DGPS Resources Differential GPSDifferential GPS (DGPS) http://www.edu- (DGPS) http://www.edu-

observatory.org/gps/dgps.htmlobservatory.org/gps/dgps.html J.A. Murray and R.L. Beard Space Navigation and Time 1985 http://ncst-J.A. Murray and R.L. Beard Space Navigation and Time 1985 http://ncst-

www.nrl.navy.mil/NCSTOrigin/Timation.htmlwww.nrl.navy.mil/NCSTOrigin/Timation.html Bradford Parkinson and Ronald BeardBradford Parkinson and Ronald Beard A History of Satellite Navigation 1995 A History of Satellite Navigation 1995

http://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.html Navigation Satellites & GPSNavigation Satellites & GPS http://www.vectorsite.net/ttgps.html http://www.vectorsite.net/ttgps.html