LORAN and Decca Navigator
“The design of GPS is based partly on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator System developed in the early 1940s, and used during World War II .” [4] “LORAN is an American development, advancing the technology of the British GEE radio navigation system that was used early in World War
II. While GEE (Generalized Estimated Equation) had a range of about 400 miles (644 km), initial LORAN systems had a range of 1,200 miles (1,930 km). It originally was known as "LRN" for Loomis Radio Navigation, after Alfred Lee Loomis, who invented the longer range system and played a crucial role in military research and development during World War II, but later was renamed to the abbreviation for the more descriptive term. LORAN systems were built during World War II after development at the Massachusetts Institute of Technology (MIT) Radiation Laboratory and were used extensively by the US Navy and Royal Navy .“ [5] “The navigational method provided by
LORAN is based on measuring the time difference between the reception of signals from a pair of radiotransmitters.” [6]
Fig.1 LORAN Monitor Lab, 1959 [1]
1

Fig.2 LORAN Station, 1945
“The Decca Navigator System was a low frequency radio navigation system which allowed ships and aircraft to determine their position by receiving radio signals from fixed navigational beacons with a receiving unit. The system used frequencies from 70 to 129 kHz. It was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings.” [7]
Fig. 3 Decca Navigator[3]
“The Decca Navigator System consisted of a number of land-based radio beacons organized into chains. Each chain consisted of a Master station and three (occasionally two) Slave stations, termed Red, Green and Purple. Ideally, the Slaves would be positioned at the vertices of an equilateral triangle with the Master at the center. The baseline length, that is, the Master-Slave distance, was typically 60~120 nautical miles.
Each station transmitted a continuous wave signal that, by comparing the phase difference of the signals from the Master and one of the Slaves, resulted in a set of hyperbolic lines of position called a pattern.” [8]
2

This figure illustrates the 20 second transmission sequence for MP Decca Navigation chain. Hatched periods denote 8.2f transmissions for chain control and surveillance. (Graphic courtesy of The Decca Navigator Co )[3a ]
General Relativity Test
“In a 1955 Friedwart Winterberg, a German-American theoretical physicist, proposed a test of General Relativity using accurate atomic clocks placed in orbit in artificial satellites.[16][17] At that time atomic clocks were not yet of the required accuracy and artificial satellites did not exist. Werner Heisenberg wrote a letter to Winterberg in 1957 in which he said the idea sounded "very interesting".[18] This idea was later experimentally verified by Hafele and Keating in 1971 by flying atomic clocks on commercial jets.[19] The theoretical approach was the same as that used by Friedwart
Winterberg. Today atomic clocks and relativistic corrections are used in GPS and it is said GPS could not function without them.”
Sputnik
“Additional inspiration for GPS came when the Soviet Union launched the first manmade satellite, Sputnik in 1957. It was launched into an elliptical low earth orbit. The satellite travelled at about 18,000 miles per hour, taking 96.2 minutes to complete each orbit. It transmitted on 20.005 and 40.002 MHz which were monitored by amateur radio operators throughout the world.
”
3

Fig.4 First manmade satellite “Sputnik1”
Radio Transmissions
Two American physicists, William Guier and George Weiffenbach, at Johns
Hopkins's Applied Physics Laboratory (APL), decided on their own to monitor Sputnik's radio transmissions.[5] Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit from the Doppler shift. The
Director of the APL gave them access to their UNIVAC (UNIVersal Automatic Computer I) to do the heavy calculations required.[9] The next step of the two scientists was focused on calculations where known location of the satellite helped to find own location on the ground. Future findings led Applied Physics Laboratory to develop Transit. [10]
Satellite Navigation Systems
The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed theTimation satellite that proved the ability to place accurate clocks in space, a technology required by GPS.[4] The TRANSIT system was made obsolete by the Global Positioning System, and ceased navigation service in 1996. Improvements in electronics allowed the GPS system to effectively take several fixes at once, greatly reducing the complexity of deducing a position. The GPS system uses many more satellites than were used with TRANSIT, allowing the system to be used continuously, while TRANSIT provided a fix only every hour or more. The basic operating principle of
TRANSIT is similar to the system used by emergency locator transmitters, except their ground transmitters and orbital receiver. Details on the signal are forwarded directly to ground stations, which then generate a fix on the transmitter using a process similar to
TRANSIT. [20]
4

Fig. 5 Transit Satellite Tracking Station Equipment
Timation
Naval Research Laboratory (NRL) scientist Rogerl L. Easton formulated a concept in
April 1964 for transmitting ranging signals along with the primary CW signal such that the distance to the target satellite could also be measured, making early orbit determination. This idea led to the concept of a new generation satellite-based navigation system, called TIMATION, which would use ranging from satellites.
NRL began the TIMATION project to provide both accurate position and precise time to passive terrestrial observers. (A "passive" user is not required to emit a signal.)
Precise space-borne clocks would be regularly updated by a master clock on the ground. These would be linked to the user's receiving equipment by ranging signals broadcast by the satellites.
NRL scientists recognized that the TIMATION concept not only could accelerate and simplify the positioning process but could make it more accurate. However, passive ranging requires an accurate and stable oscillator in the satellite. The TIMATION
Project, under the direction of Roger L. Easton, concentrated on developing an improved quartz frequency standard for satellites and determining the most effective satellite constellation for providing worldwide coverage.
NRL also identified orbits that would maintain a consistent ground track so that an almanac of satellite positions could be published and the satellite would not be required to transmit its position. Simplified receiving equipment could then be used, and the techniques of celestial navigation could be employed for simple and accurate navigation and time determination.[21]
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Fig. 6 Timation I first satellite, http://ncst-www.nrl.navy.mil/NCSTOrigin/TIMATsm.gif
OMEGA
In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Omega Navigation System was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations. It enabled ships and aircraft to determine their position by receiving very low frequency radio signals transmitted by a network of fixed terrestrial radio beacons, using a receiver unit. It became operational around 1971 and was shut down in 1997. Each Omega station transmitted a sequence of three radio signals plus a fourth frequency which was unique to each of the eight stations. The duration of each differed in a fixed pattern, and repeated every ten seconds; the tensecond pattern was common to all eight stations and synchronized with the carrier phase angle, which itself was synchronized with the local master atomic clock. [22]
NAVSTAR
The TIMATION Project gave birth to the NAVSTAR Global Positioning System
Program. While the Air Force became the executive service, the Navy, and in particular
NRL, participated heavily in the system concept and technologies. The NAVSTAR GPS development plans in 1973 called for NRL to continue the technology efforts begun in the TIMATION Project. NRL's work was considered vital to the time-based system concept, and the Deputy Secretary of Defense called for Navy participation with emphasis on the clock developments. A cesium standard development proposed by
NRL was selected the as the most likely satellite clock candidate for meeting the ultimate requirements. NRL's third TIMATION satellite was renamed Navigation
Technology Satellite 1 (NTS-1) at its launch in July 1974, one year after the start of the
GPS Program. It was the first satellite to fly atomic clocks, and examined two experimental rubidium frequency standards operating in space. NTS-2 was launched in
June 1977 and orbited the first cesium clock in space. NTS-2 was used to evaluate the stations, software, and systems for the first developmental NAVSTAR satellites that were launched in 1978.
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Chapter II
Concept of GPS
The current GPS consists of three major segments. These are the space segment
(SS), a control segment (CS). The U.S. Air Force develops, maintains, and operates the space and control segments. GPS satellites broadcast signals from space, and each
GPS receiver uses these signals to calculate its three-dimensional location
(latitude, longitude, and altitude) and the current time.
The space segment is composed of 24 to 32 satellites in medium Earth orbit and also includes the payload adapters to the boosters required to launch them into orbit.
The control segment is composed of a master control station, an alternate master control station, and a host of dedicated and shared ground antennas and monitor stations.
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Fig.7 GPS constellation, http://www.gps.gov/multimedia/images/
The space segment (SS) is composed of the orbiting GPS satellites in GPS parlance. The GPS design originally called for 24 satellites, eight each in three approximately circular orbits, but this was modified to six orbital planes with four satellites each. The orbits are centered on the Earth, not rotating with the Earth, but instead fixed with respect to the distant stars. The six orbit planes have approximately
55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection). The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface. The result of this objective is that the four satellites are not evenly spaced (90 degrees) apart within each orbit. In general terms, the angular difference between satellites in each orbit is 30, 105,
120, and 105 degrees apart which, of course, sum to 360 degrees.
The GPS control segment consists of a global network of ground facilities that track the GPS satellites, monitor their transmissions, perform analyses, and send commands and data to the constellation. The current operational control segment includes a master control station, an alternate master control station, 12 command and control antennas, and 16 monitoring sites.
The master control station in Colorado performs the primary control segment functions, providing command and control of the GPS constellation. The MCS generates and uploads navigation messages and ensures the health and accuracy of the satellite constellation. It receives navigation information from the monitor stations,
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utilizes this information to compute the precise locations of the GPS satellites in space, and then uploads this data to the satellites.
Monitor stations track the GPS satellites as they pass overhead and channel their observations back to the master control station. Monitor stations collect atmospheric data, range/carrier measurements, and navigation signals. The sites utilize sophisticated GPS receivers and are operated by the MCS.
Ground antennas are used to communicate with the GPS satellites for command and control purposes. These antennas support S-band communications links that send/transmit navigation data uploads and processor program loads, and collect telemetry. The ground antennas are also responsible for normal command transmissions to the satellites. [23] A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high above the Earth. Each satellite continually transmits messages that include: the time the message was transmitted satellite position at time of message transmission.
The receiver uses the messages it receives to determine the transit time of each message and computes the distance to each satellite using the speed of light. Each of these distances and satellites' locations define a sphere. The receiver is on the surface of each of these spheres when the distances and the satellites' locations are correct.
These distances and satellites' locations are used to compute the location of the receiver using the navigation equations. This location is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included.
Many GPS units show derived information such as direction and speed, calculated from position changes.
Chapter III
Military to Civilian Transition
While originally a military project, GPS is considered a dual-use technology, meaning it has significant military and civilian applications. In 1983 President Ronald
Reagan issued a directive making GPS freely available for civilian use. The first satellite was launched in 1989, and the 24th satellite was launched in 1994. GPS has become a widely deployed and useful tool for commerce, scientific uses, tracking, and surveillance. GPS's accurate time facilitates everyday activities such as banking, mobile phone operations, and even the control of power grids by allowing well synchronized hand-off switching.
There are several navigational systems that were developed using similar methods in Russia-Glonass, China-COMPASS, India-IRNSS, Japan-QZSS and
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European Union-GALILEO. GLONASS is a radio-based satellite navigation system operated for the Russian government by the Russian Aerospace Defense
Forces. It both complements and provides an alternative to the United States' Global
Positioning System (GPS) and is the only alternative navigational system in operation with global coverage and of comparable precision. Development of GLONASS began in the Soviet Union in 1976. Beginning on 12 October 1982, numerous rocket launches added satellites to the system until the "constellation" was completed in 1995. By 2010,
GLONASS had achieved 100% coverage of Russia's territory and in October 2011, the full orbital constellation of 24 satellites was restored, enabling full global coverage. The
GLONASS satellites' designs have undergone several upgrades, with the latest version being GLONASS-K.
According to Russian System of Differential Correction and Monitoring's data, as of
2010, precisions of GLONASS navigation definitions (for p=0.95) for latitude and longitude were 4.46
—7.38 m with mean number of NSV equals 7—8 (depending on station). In comparison, the same time precisions of GPS navigation definitions were
2.00
—8.76 m with mean number of NSV equals 6—11 (depending on station. Civilian
GLONASS used alone is therefore very slightly less accurate than GPS. On high latitudes (north or south), GLONASS' accuracy is better than that of GPS due to the orbital position of the satellites. [26]
BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and offers limited coverage and applications. It has been offering navigation services, mainly for customers in China and neighboring regions, since 2000. The second generation of the system, known as Compass or BeiDou-2, will be a global satellite navigation system consisting of 35 satellites, and is under construction as of September 2012. It became operational in China in December 2011, with 10 satellites in use. It is planned to offer services to customers in the Asia-
Pacific region by 2012, and to global customers upon its completion in 2020.[27]
The Indian Regional Navigational Satellite System (IRNSS) is an autonomous regional satellite navigation system being developed by the Indian Space Research
Organization which would be under total control of Indian government. The requirement of such a navigation system is driven by the fact that access to Global Navigation
Satellite Systems, GPS, is not guaranteed in hostile situations. The IRNSS would provide two services, with the Standard Positioning Service open for civilian use and the
Restricted Service, encrypted one, for authorized users. [28]
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and Satellite Based Augmentation System for the Global
Positioning System, that would be receivable within Japan. The first satellite 'Michibiki' was launched on 11 September 2010. Full operational status is expected by 2013.
QZSS is targeted at mobile applications, to provide communications-based services
(video, audio, and data) and positioning information. With regards to its positioning
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service, QZSS can only provide limited accuracy on its own and is not currently required in its specifications to work in a stand-alone mode.[29]
Galileo is a global navigation satellite system currently being built by the European
Union and European Space Agency. One of the aims of Galileo is to provide a highprecision positioning system upon which European nations can rely, independently from the Russian GLONASS, US GPS, and Chinese Compass systems, which can be disabled in times of war or conflict. On 21 October 2011 the first two of four operational satellites were launched to validate the system. The next two followed on 12 October
2012. Once this In-Orbit Validation (IOV) phase has been completed, additional satellites will be launched to reach Initial Operational Capability (IOC) around middecade. Full completion of the 30 satellites Galileo system (27 operational + 3 active spares) is expected by 2019.
Basic navigation services will be free of charge. Galileo is intended to provide horizontal and vertical positions measurements within 1 meter precision and better positioning services at high latitudes than other positioning systems. As a further feature, Galileo will provide a unique global Search and Rescue (SAR) function.
Satellites will be equipped with a transponder which will relay distress signals from the user's transmitter to the Rescue Co-ordination Centre, which will then initiate the rescue operation. At the same time, the system will provide a signal to the user, informing them that their situation has been detected and that help is on the way. This latter feature is new and is considered a major upgrade compared to the existing GPS and GLONASS navigation systems, which do not provide feedback to the user. The use of basic (low-precision) Galileo services will be free and open to everyone.[30]
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Chapter IV
Future Development
The United States government is in the process of fielding three new signals designed for civilian use: L2C, L5, and L1C. The legacy civil signal, called L1 C/A or C/A at L1, will continue broadcasting in the future, for a total of four civil GPS signals. Users must upgrade their equipment to benefit from the new signals. The new civil signals are phasing in incrementally as the Air Force launches new GPS satellites to replace older ones. Most of the new signals will be of limited use until they are broadcast from 18 to
24 satellites.
L2C is the second civilian GPS signal, designed specifically to meet commercial needs. When combined with L1 C/A in a dual-frequency receiver, L2C enables ionospheric correction, a technique that boosts accuracy. Civilians with dual-frequency
GPS receivers enjoy the same accuracy as the military. For professional users with existing dual-frequency operations, L2C delivers faster signal acquisition, enhanced reliability, and greater operating range. L2C broadcasts at a higher effective power than the legacy L1 C/A signal, making it easier to receive under trees and even indoors. The first GPS IIR(M) satellite featuring L2C launched in 2005. Every GPS satellite fielded since then has included an L2C transmitter. The name "L2C" refers to the radio frequency used by the signal (1227 MHz, or L2) and the fact that it is for civilian use.
There are also two military signals at the L2 frequency.
L5 is the third civilian GPS signal, designed to meet demanding requirements for safety-of-life transportation and other high-performance applications. L5 is broadcast in a radio band reserved exclusively for aviation safety services. It features higher power, greater bandwidth, and an advanced signal design. Future aircraft will use L5 in combination with L1 C/A to improve accuracy (via ionospheric correction) and robustness (via signal redundancy). In addition to enhancing safety, L5 use will increase capacity and fuel efficiency within U.S. airspace, railroads, waterways, and highways.
Beyond transportation, L5 will provide users worldwide with the most advanced civilian
GPS signal. When used in combination with L1 C/A and L2C, L5 will provide a highly robust service. Through a technique called trilaning, the use of three GPS frequencies may enable sub-meter accuracy without augmentations, and very long range operations with augmentations. In 2009, the Air Force successfully broadcast an experimental L5 signal on the GPS IIR-20(M) satellite. The first GPS IIF satellite with a full L5 transmitter
12

was launched in May 2010. The name "L5" refers to the U.S. designation for the radio frequency used by the signal (1176 MHz).[31]
[1] Retrieved October 18, 2012, from http://www.loranhistory.info/lms_shetlands/shetlands.htm
[3] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/File:Decca_Navigator_Mk_12.jpg
[3a] Retrieved October 18, 2012, from http://www.jproc.ca/hyperbolic/decca_trans.html
[4] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/Global_Positioning_System
Fig.4 Retrieved October 18, 2012, from http://commons.wikimedia.org/wiki/File:Sputnik_asm.jpg?uselang=en
Fig.5 Retrieved October 18, 2012 , from http://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Doppler_019_inside%2C_M cMurdo_Station%2C_1974.png/500px-
Doppler_019_inside%2C_McMurdo_Station%2C_1974.png
[5] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/LORAN
[6] Appleyard, S.F.; Linford, R.S. and Yarwood, P.J. (1988). Marine Electronic
Navigation (2nd Edition). Routledge & Kegan Paul. pp. 77
–83. ISBN 0-7102-1271-2
[7], [8] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/Decca_Navigator_System
[9] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/UNIVAC_I
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[10] Steven Johnson (2010), Where good ideas come from, the natural history of innovation, New York: Riverhead Books
[16] Winterberg, Relativistische Zeitdilatation eines künstlichen Satelliten, Astronautica
Acta, Vol. 2, no. 1, pp. 25-29 1956
[17] Retrieved October 18, 2012, from http://bourabai.kz/winter/satelliten.htm
[18] Winterberg, Friedwardt (2002). The Planck Aether Hypothesis: An Attempt for a
Finitistic Non-Archimedean Theory of Elementary Particles, p. 262
[19] Hafele, Joseph C.; Keating, Richard E. (July 14, 1972). "Around-the-World Atomic
Clocks: Observed Relativistic Time Gains". pp 168 –170.
[20] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/Transit_(satellite)
[21] Retrieved October 18, 2012, from http://ncstwww.nrl.navy.mil/NCSTOrigin/Timation.html
[22] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/Omega_Navigation_System
[23] Retrieved October 18, 2012, from http://www.gps.gov/systems/gps/control/
[26] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/GLONASS
[27] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/COMPASS_navigation_system
[28] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/IRNSS
[29] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/QZSS
[30] Retrieved October 18, 2012, from http://en.wikipedia.org/wiki/Galileo_(satellite_navigation)
[31] Retrieved October 18, 2012, from http://www.gps.gov/systems/gps/modernization/civilsignals/
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