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The concept that led to growth of the satellite navigation methods dates back to 1957 and the primary launch of an artificial satellite into orbit, Russia’s Sputnik I. Dr. William H. Guier and Dr. George C. Wieffenbach at the Applied Physics Laboratory of the Johns Hopkins University have been monitoring the well-known "beeps" transmitted by the passing satellite tv for pc. They plotted the received alerts at precise intervals, and noticed that a characteristic Doppler curve emerged. Since satellites usually follow fixed orbits, they reasoned that this curve could possibly be used to describe the satellite’s orbit. They then demonstrated that they might decide all of the orbital parameters for a passing satellite by Doppler observation of a single go from a single mounted station. The Doppler shift apparent while receiving a transmission from a passing satellite tv for pc proved to be an effective measuring device for establishing the satellite tv for pc orbit. Dr. Frank T. McClure, additionally of the Applied Physics Laboratory, reasoned in reverse: If the satellite tv for pc orbit was known, Doppler shift measurements could possibly be used to find out one’s place on Earth.

His studies in support of this speculation earned him the primary National Aeronautics and Space Administration award for vital contributions to space growth. In 1958, the Applied Physics Laboratory proposed exploring the potential of an operational satellite Doppler navigation system. The Chief of Naval Operations then set forth requirements for such a system. The primary successful launching of a prototype system satellite tv for pc in April 1960 demonstrated the Doppler system’s operational feasibility. The Navy Navigation Satellite System (NAVSAT, also called TRANSIT) was the primary operational satellite navigation system. The system’s accuracy was better than 0.1 nautical mile wherever in the world, although its availability was considerably restricted. It was used primarily for the navigation of floor ships and submarines, but it surely additionally had some functions in air navigation. It was also utilized in hydrographic surveying and geodetic position determination. The Federal Radionavigation Plan has designated the NAVigation System utilizing Timing And Ranging (NAVSTAR) Global Positioning System (GPS) as the primary navigation system of the U.S.

GPS is a spaced-based radio positioning system which offers suitably geared up customers with extremely correct position, velocity, and time data. It consists of three main segments: a space segment, a management section, and a person section. The space section includes some 24 satellites. Spacing of the satellites in their orbits is organized in order that not less than 4 satellites are in view to a consumer at any time, anywhere on the Earth. Each satellite transmits signals on two radio frequencies, superimposed on that are navigation and system information. Included on this information are predicted satellite ephemeris, atmospheric propagation correction knowledge, satellite clock error information, and satellite tv for pc well being information. This phase normally consists of 21 operational satellites with three satellites orbiting as lively spares. The satellites orbit at an altitude of 20,200 km, in six separate orbital planes, every airplane inclined 55° relative to the equator. The satellites complete an orbit approximately as soon as each 12 hours. GPS satellites transmit pseudorandom noise (PRN) sequence-modulated radio frequencies, designated L1 (1575.Forty two MHz) and L2 (1227.60 MHz).

The satellite tv for pc transmits both a Coarse Acquisition Code (C/A code) and a Precision Code (P code). Both the P and C/A codes are transmitted on the L1 provider; only the P code is transmitted on the L2 carrier. Superimposed on both the C/A and P codes is the navigation message. This message incorporates the satellite tv for pc ephemeris information, atmospheric propagation correction data, and satellite tv for pc clock bias. GPS assigns a singular C/A code and a singular P code to every satellite. This observe, known as code division a number of entry (CDMA), permits all satellites the use of a typical carrier frequency whereas nonetheless permitting the receiver to determine which satellite tv for pc is transmitting. CDMA also permits for simple consumer identification of every GPS satellite tv for pc. Since each satellite broadcasts utilizing its personal distinctive C/A and P code combination, it can be assigned a novel PRN sequence number. This number is how a satellite tv for pc is recognized when the GPS control system communicates with users about a particular GPS satellite tv for pc.

The control phase includes a grasp control station (MCS), various monitor ItagPro stations, and ground antennas located all through the world. The grasp control station, located in Colorado Springs, Colorado, ItagPro consists of gear and services required for satellite tv for pc monitoring, telemetry, tracking, commanding, control, uploading, and navigation message era. The monitor stations, ItagPro positioned in Hawaii, Colorado Springs, Kwajalein, Diego Garcia, and Ascension Island, passively track the satellites, accumulating ranging knowledge from the satellites’ signals and relaying them to the MCS. The MCS processes this info to find out satellite tv for pc position and signal knowledge accuracy, updates the navigation message of every satellite tv for pc and relays this information to the ground antennas. The ground antennas then transmit this data to the satellites. The ground antennas, situated at Ascension Island, Diego Garcia, and Kwajalein, are additionally used for transmitting and receiving satellite control info. The user equipment is designed to receive and iTagPro support process indicators from four or extra orbiting satellites either simultaneously or sequentially. The processor within the receiver then converts these signals to navigation data.