Richard Presentation

7/27/2019 Richard Presentation

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Evolution of Military GPS

Deployment of Sputnik and its Doppler Shift

Doppler Data and the Birth of the Transit

System and Timation System Early GPS

Today GPS

Richard Stewart


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Sputnik: Learning From OurRivals

In 1957, the Soviets successfullylaunched Sputnik into space. It wasthe size of a basketball and weighedabout 180 pounds.

The Soviets success embarrassed theUnited States who thought they werethe worlds most advanced industrialnation. As a result of their humiliation,the country took an active role intoresearching military precision.

The Department of Defenses primarypurposes in developing a GlobalPosition System was to use it inprecision weapon delivery


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Sputnik: Learning From OurRivals

Studying the Doppler Shift of the Sputnik, the Johns HopkinsApplied Physics Lab recognized a variance of the Sputnik signalin comparison of its position. As the fast-moving Sputnikapproached, the scientists noted that signal frequency washigher than the transmitted frequency. They also observed thatthe frequency lowered until the satellite reached its closet pointof approach (CPA), when the observed frequency equaled the

transmitted frequency. The frequency decreased as Sputnikmoved farther away, although the rate of decrease slowed withincreasing distance from the observers. This Doppler shiftphenomenon that the scientists observed was the same one youexperience when an express train rushes by you at a localstation and you hear its roaring sound drop sharply in pitch.

At the end of their experiments, the scientists reasoned that theycould accurately locate their position on earth by carefully

measuring the satellite's Doppler shift and knowing the satellite'sposition in orbit at the exact instant of each measurement.


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Doppler Data and the Birth of the TransitSystem and Timation System

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

Transit was the first operational satellite-based navigationsystem which included seven low-altitude (1075 km) polar-

orbiting satellites In Transit

1. a satellite broadcasted radio signals2.the ground stations tracked the satellite3. facilities updated satellite orbital parameters

The result- transit users determined their position on earth

by measuring the Doppler shift signals transmitted by thesatellites


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Transit

Developed to provide accurate navigation datafor Polaris missile submarines and other shipsat the ocean surface

The way it worked Doppler-shifted signals enabled a determination

of the orbit using data recorded at one siteduring a single pass of the satellite. So if asatellites orbit was known, a radio receiversposition could be determined from the sameDoppler measurements.

Unlike the Doppler data used to track theSputnik satellite, Transit satellites could be

precisely determined by tracking them at widelyspaced fixed sites.

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


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Positives and Negatives of Transit

Positives Proof that a space system could offer excellent

positioning reliability Was available to civilian users in 1967 including

commercial marine navigators and personal crafts Created technologies

Negatives Large gaps in coverage

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

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


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Negatives cont.

The process was slow and required longobservation time

Only provided two-dimensional positioning

Transit was not efficient for the more highvelocity technology (aircrafts, missiles, etc.)being developed by the military

Nevertheless, the Transit system continuedto be used until 1996 after about 33 years ofservice.


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Timation

Timation was a spaced-based navigation systemtechnology program thatwas developed in 1964 bythe Navy.

Advanced thedevelopment of thestability of clocks (timeprecision), time-transfer,and two-dimensional

navigation. 1967- First Timation

satellite launched


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Timation Models

The first satellite used a very stable quartz-crystal oscillators

Later models incorporated the first atomicfrequency stability

Atomic clocks have better frequency stabilitythan earlier clocks=better prediction of satellite

orbits


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Timation Contribution

Development in the atomic clock for satellitenavigation

The last two Timation satellites were used as

GPS prototypes

Navigation Technology

Satellite 1 (3rd satellite)


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System 621B

Around the same time the Navy was developingTimation, the Air Force worked with a designconcept using a similar technology program called

System 621B. Biggest Improvement- 3 dimensional navigation!!!

(latitude, longitude, and altitude)

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


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System 621B

System originated at the AerospaceCorporation in 1963 developed for precisepositioning of aircrafts

By Oct. 1963, System 621B was successfulenough to get Air Force supporting andfunding

Around 1972, ran a series or aircraft tests inNew Mexico using a ground and airtransmitters to simulate satellitesresult


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White Sands Proving Ground in NewMexico

Pseudorandom noise pinpointedthe positions of aircrafts to withina hundredth of a mile= 16 meters

PRN technique had the capabilityto reject interference noiseincluding jamming or deliberateinterference. PRN techniquesallow all satellites to transit on

same frequency, therefore acommunication channel could beadded permitting user to receiverdata (satellite location and clock

information.


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Military Division

By the late 1960s, the U.S. Navy, Air Force, andArmy worked independently on radio navigationsystems that would provide all-weather, 24-hour

coverage, and accuracies that would enhance themilitary capabilities of their respective forces.

John Hopkins Applied Physics Laboratory-Transit

Naval Research Laboratory-Timation Army-SECOR (Sequential Correlation of Range)


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Military Unity

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

What NAVSEG had to determine? How many satellites?

What altitude?

What would be the signal codes

What would be the modulation techniques

Cost


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Early GPS

September 1973, a system was developedcombining early Navy and Air Forceprograms called NAVSTAR GPS

System merged System 621B and Timationtechnology Satellites orbits were based on Timation but would

have a higher altitude.

Signal structure and frequencies were based onSystem 621B

Satellites would use atomic clocks


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3-Phase Development of theNAVSTAR GPS

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

refurbished Timation satellitescarrying the first atomic clocks everlaunched into space

(1978-1985)- Rockwell International

Built a total of eleven Block Isatellites launched on the Atlas-Fbooster.

Design life was only 3 years butmany last 10+ years

6th Block I satellite carried a nuclearexplosion detection sensor whichwas launched on April 36, 1980

Block I satellites were being testedfor on aircraft, helicopter, ships,trucks, jeeps, and even by menusing 25-pound backpacks.


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2nd Stage of GPS

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

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

3 on-orbit spares)

Development of Block II satellites were dropped

Increased the interest in the program bystressing that GPS could increase bombingaccuracy


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Block II Satellites

With a renew interest bythe Secretary of Defense,Block II satellites weredeveloped and launched in

Feb. 1989 Operational by April

1989/created RockwellInternational Improvements

Full selective availability/advanced system securities

Improved reliability andsurvivability


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3rd Phase

Launch of the Block II/IIA/IIR and finally IIRcombining up to 33 satellites (including spares) toconsist of our new GPS. GPS today uses 24

satellites and numerous ground stations

LAND SEA AIR

Able to get quick accurate readings no matter the weathercondition, time of day, or velocity
http://www.ecosystems-management.com.au/images/gps.jpg


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Bibliography

Steven R. StromChart ing a Course Toward Glob al Navigat ionhttp://www.aero.org/publications/crosslink/summer2002/01.html

History o f GPShttp://www.bugclub.org/beginners/history/gps.html

Mary BellisGlobal Posit ion ing System - GPShttp://inventors.about.com/library/inventors/blgps.htm

Robert A. NelsonThe Global Positioning SystemVia Satellite, November1999 http://www.aticourses.com/global_positioning_system.htm

Sam Wormleys DGPS Resources Differential GPS (DGPS) http://www.edu-observatory.org/gps/dgps.html

J.A. Murray and R.L. Beard Space Navigatio n and Tim e 1985http: / /ncst-www.nr l .navy.mil /NCSTOrigin/Timat ion.html

Bradford Parkinson and Ronald BeardA History of Satellite Navigation 1995

http://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.html Navigation Satellites & GPShttp://www.vectorsite.net/ttgps.html
http://www.aero.org/publications/crosslink/summer2002/contributors.htmlhttp://www.aero.org/publications/crosslink/summer2002/01.htmlhttp://www.bugclub.org/beginners/history/gps.htmlhttp://inventors.about.com/library/inventors/blgps.htmhttp://www.aticourses.com/global_positioning_system.htmhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://www.vectorsite.net/ttgps.htmlhttp://www.vectorsite.net/ttgps.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://ncst-www.nrl.navy.mil/NCSTOrigin/Timation.htmlhttp://www.aticourses.com/global_positioning_system.htmhttp://inventors.about.com/library/inventors/blgps.htmhttp://www.bugclub.org/beginners/history/gps.htmlhttp://www.aero.org/publications/crosslink/summer2002/01.htmlhttp://www.aero.org/publications/crosslink/summer2002/contributors.html

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