1 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

2 Sputnik: Learning From Our Rivals  In 1957, the Soviets successfully launched Sputnik into space. It was the size of a basketball and weighed about 180 pounds.  The Soviets’ success embarrassed the United States who thought they were the world’s most advanced industrial nation. As a result of their humiliation, the country took an active role into researching military precision.  The Department of Defenses primary purposes in developing a Global Position System was to use it in precision weapon delivery

3 Sputnik: Learning From Our Rivals  Studying the Doppler Shift of the Sputnik, the Johns Hopkins Applied Physics Lab recognized a variance of the Sputnik signal in comparison of its position. As the fast-moving Sputnik approached, the scientists noted that signal frequency was higher than the transmitted frequency. They also observed that the frequency lowered until the satellite reached its closet point of approach (CPA), when the observed frequency equaled the transmitted frequency. The frequency decreased as Sputnik moved farther away, although the rate of decrease slowed with increasing distance from the observers. This Doppler shift phenomenon that the scientists observed was the same one you experience when an express train rushes by you at a local station and you hear its roaring sound drop sharply in pitch.  At the end of their experiments, the scientists reasoned that they could accurately locate their position on earth by carefully measuring the satellite's Doppler shift and knowing the satellite's position in orbit at the exact instant of each measurement.

4 Doppler Data and the Birth of the Transit System and Timation System  Under the direction of Dr. Richard Kirschner, the John Hopkins Applied Physics Laboratory created the Transit. Transit was conceived in the late 1950s and deployed in the mid-1960s  Transit was the first operational satellite-based navigation system which included seven low-altitude (1075 km) polar- orbiting satellites  In Transit 1. a satellite broadcasted radio signals 2.the ground stations tracked the satellite 3. facilities updated satellite orbital parameters  The result- transit users determined their position on earth by measuring the Doppler shift signals transmitted by the satellites

5 Transit  Developed to provide accurate navigation data for Polaris missile submarines and other ships at the ocean surface  The way it worked –Doppler-shifted signals enabled a determination of the orbit using data recorded at one site during a single pass of the satellite. So if a satellite’s orbit was known, a radio receiver’s position could be determined from the same Doppler measurements. –Unlike the Doppler data used to track the Sputnik satellite, Transit satellites could be precisely determined by tracking them at widely spaced fixed sites.  A satellite had a 107 min. period of revolution- under favorable conditions accuracy was between 35 and 100m.

6 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

7 Negatives cont. –The process was slow and required long observation time –Only provided two-dimensional positioning –Transit was not efficient for the more high velocity technology (aircrafts, missiles, etc.) being developed by the military  Nevertheless, the Transit system continued to be used until 1996 after about 33 years of service.

8 Timation  Timation was a spaced- based navigation system technology program that was developed in 1964 by the Navy.  Advanced the development of the stability of clocks (time precision), time-transfer, and two-dimensional navigation.  First Timation satellite launched

9 Timation Models  The first satellite used a very stable quartz- crystal oscillators  Later models incorporated the first atomic frequency stability –Atomic clocks have better frequency stability than earlier clocks=better prediction of satellite orbits

10 Timation Contribution  Development in the atomic clock for satellite navigation  The last two Timation satellites were used as GPS prototypes Navigation Technology Satellite 1 (3 rd satellite)

11 System 621B  Around the same time the Navy was developing Timation, the Air Force worked with a design concept 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 of satellite ranging signal called pseudorandom noise (PRN)

12 System 621B  System originated at the Aerospace Corporation in 1963 developed for precise positioning of aircrafts  By Oct. 1963, System 621B was successful enough to get Air Force supporting and funding  Around 1972, ran a series or aircraft tests in New Mexico using a ground and air transmitters to simulate satellites…result…

13 White Sands Proving Ground in New Mexico  Pseudorandom noise pinpointed the positions of aircrafts to within a hundredth of a mile= 16 meters  PRN technique had the capability to reject interference noise including jamming or deliberate interference. PRN techniques allow all satellites to transit on same frequency, therefore a communication channel could be added permitting user to receiver data (satellite location and clock information.

14 Military Division  By the late 1960s, the U.S. Navy, Air Force, and Army worked independently on radio navigation systems that would provide all-weather, 24-hour coverage, and accuracies that would enhance the military capabilities of their respective forces.  John Hopkins Applied Physics Laboratory-Transit  Naval Research Laboratory-Timation  Army-SECOR (Sequential Correlation of Range)

15 Military Unity  1968-Department of Defense steps in creates a joint 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

16 Early GPS  September 1973, a system was developed combining early Navy and Air Force programs called NAVSTAR GPS –System merged System 621B and Timation technology  Satellites orbits were based on Timation but would have a higher altitude.  Signal structure and frequencies were based on System 621B  Satellites would use atomic clocks

17 3-Phase Development of the NAVSTAR GPS  ( )- $100 million program –First two NAVSTAR satellites were refurbished Timation satellites carrying the first atomic clocks ever launched into space  ( )- Rockwell International –Built a total of eleven Block I satellites launched on the Atlas-F booster. –Design life was only 3 years but many last 10+ years  6 th Block I satellite carried a nuclear explosion detection sensor which was launched on April 36, 1980 –Block I satellites were being tested for on aircraft, helicopter, ships, trucks, jeeps, and even by men using 25-pound backpacks.

18 2 nd Stage of GPS  Funding cut!!!- Secretary of Defense cut program by 30% ($500 million)  Result- –Number of satellites were cut down: (plus 3 on-orbit spares) –Development of Block II satellites were dropped  Increased the interest in the program by stressing that GPS could increase bombing accuracy

19 Block II Satellites  With a renew interest by the Secretary of Defense, Block II satellites were developed and launched in Feb  Operational by April 1989/created Rockwell International –Improvements  Full selective availability/ advanced system securities  Improved reliability and survivability

20 3 rd Phase  Launch of the Block II/IIA/IIR and finally IIR combining up to 33 satellites (including spares) to consist of our new GPS. GPS today uses 24 satellites and numerous ground stations LAND SEAAIR Able to get quick accurate readings no matter the weather condition, time of day, or velocity

21 Bibliography  Steven R. Strom Charting a Course Toward Global Navigation Steven R. Strom Steven R. Strom  History of GPS  Mary Bellis Global Positioning System - GPS  Robert A. Nelson The Global Positioning System Via Satellite, November  Sam Wormley’s DGPS Resources Differential GPS (DGPS) observatory.org/gps/dgps.html  J.A. Murray and R.L. Beard Space Navigation and Time  Bradford Parkinson and Ronald Beard A History of Satellite Navigation  Navigation Satellites & GPS