Friday, January 11, 2013

Global Positioning System,, The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The system provides critical capabilities to military, civil and commercial users around the world. HP 448007-001 battery It is maintained by the United States government and is freely accessible to anyone with a GPS receiver. The GPS project was developed in 1973 to overcome the limitations of previous navigation systems,[1] integrating ideas from several predecessors, including a number of classified engineering design studies from the 1960s. HP Pavilion DV7 battery GPS was created and realized by the U.S. Department of Defense (DoD) and was originally run with 24 satellites. It became fully operational in 1994. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS system and implement the next generation of GPS III satellites and Next Generation Operational Control System (OCX).[2] HP DV6-1120SA battery Announcements from the Vice President and the White House in 1998 initiated these changes. In 2000, U.S. Congress authorized the modernization effort, referred to as GPS III. In addition to GPS, other systems are in use or under development. The Russian Global Navigation Satellite System (GLONASS) was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s. HP DV6-1210SA battery There are also the planned European Union Galileo positioning system, Chinese Compass navigation system, andIndian Regional Navigational Satellite System. The design of GPS is based partly on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigatordeveloped in the early 1940s, and used during World War II. Compaq CQ50 battery In 1956, the German-American physicist Friedwardt Winterberg[3] proposed a test of general relativity (for time slowing in a strong gravitational field) using accurate atomic clocks placed in orbit inside artificial satellites. (To achieve accuracy requirements, GPS uses principles of general relativity to correct the satellites' atomic clocks.[4]) HP Pavilion DV8 battery Additional inspiration for GPS came when the Soviet Union launched the first man-made satellite, Sputnik in 1957. 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. Sony VGP-BPS13 battery 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 to do the heavy calculations required. The following spring, Frank McClure, the deputy director of the APL, HP DV9700 battery asked Guier and Weiffenbach to investigate the inverse problem - pinpointing the user's location given that of the satellite. (The Navy was developing the submarine-launched Polaris missile, which required them to know the submarine's location.) This led them and APL to develop the Transit system. Compaq CQ35-100 battery 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 the Timation satellite that proved the ability to place accurate clocks in space, a technology required by GPS. Sony VGP-BPS11 battery In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations,[7] became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy. Sony VAIO PCG-3B1M Battery While there were wide needs for accurate navigation in military and civilian sectors, almost none of those were seen as justification for the billions of dollars it would cost in research, development, deployment, and operation for a constellation of navigation satellites. Sony VAIO PCG-3C1T Battery During the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded. It is also the reason for the ultra secrecy at that time. The nuclear triad consisted of the United States Navy'ssubmarine-launched ballistic missiles (SLBMs) Sony VAIO PCG-3D1M Battery along with United States Air Force (USAF) strategic bombers and intercontinental ballistic missiles (ICBMs). Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier. Precise navigation would enable United States submarines to get an accurate fix of their positions prior to launching their SLBMs. Sony VAIO PCG-3G2M Battery The USAF with two-thirds of the nuclear triad also had requirements for a more accurate and reliable navigation system. The Navy and Air Force were developing their own technologies in parallel to solve what was essentially the same problem. To increase the survivability of ICBMs, Sony VAIO PCG-5R1M Battery there was a proposal to use mobile launch platforms (such as Russian SS-24 and SS-25) and so the need to fix the launch position had similarity to the SLBM situation. In 1960, the Air Force proposed a radio-navigation system called MOSAIC (MObile System for Accurate ICBM Control) that was essentially a 3-D LORAN. Sony VAIO PCG-7141M Battery A follow-on study called Project 57 was worked in 1963 and it was "in this study that the GPS concept was born." That same year the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS"[9] and promised increased accuracy for Air Force bombers as well as ICBMs. Sony VAIO PCG-7143M Battery Updates from the Navy Transit system were too slow for the high speeds of Air Force operation. The Navy Research Laboratory continued advancements with their Timation (Time Navigation) satellites, first launched in 1967, and with the third one in 1974 carrying the first atomic clock into orbit. Sony VAIO PCG-7151M Battery Another important predecessor to GPS came from a different branch of the United States military. In 1964, the United States Army orbited its first SECOR (Sequential Collation of Range) satellite used for geodetic surveying. The SECOR system included three ground-based transmitters from known locations that would send signals to the satellite transponder in orbit. Sony VAIO PCG-7154M Battery A fourth ground-based station at an undetermined position could then use those signals to fix its location precisely. The last SECOR satellite was launched in 1969.[11] Decades later during the early years of GPS, civilian surveying became one of the first fields to make use of the new technology, Sony VAIO PCG-7162M Battery because they could reap benefits of signals from the less-than-complete GPS constellation years before it was declared operational. GPS can be thought of as an evolution of the SECOR system where the ground-based transmitters have been migrated into orbit. Sony VAIO PCG-7181M Battery With these parallel developments in the 1960s, it was realized that a superior system could be developed by synthesizing the best technologies from 621B, Transit, Timation, and SECOR in a multi-service program. During Labor Day weekend in 1973, a meeting of about 12 military officers at the Pentagon discussed the creation of a Defense Navigation Satellite System (DNSS). Sony VAIO PCG-41112M Battery It was at this meeting that "the real synthesis that became GPS was created." Later that year, the DNSS program was named Navstar. With the individual satellites being associated with the name Navstar (as with the predecessors Transit and Timation), a more fully encompassing name was used to identify the constellation of Navstar satellites, Navstar-GPS, which was later shortened simply to GPS. Sony VAIO PCG-7153M Battery After Korean Air Lines Flight 007, carrying 269 people, was shot down in 1983 after straying into the USSR's prohibited airspace,[13] in the vicinity of Sakhalinand Moneron Islands, President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good. Sony VAIO PCG-71312M Battery The first satellite was launched in 1989, and the 24th satellite was launched in 1994. Initially, the highest quality signal was reserved for military use, and the signal available for civilian use was intentionally degraded (Selective Availability). This changed with President Bill Clinton ordering Selective Availability to be turned off at midnight May 1, 2000, Sony VAIO PCG-7144M Battery improving the precision of civilian GPS from 100 meters (330 ft) to 20 meters (66 ft). The executive order signed in 1996 to turn off Selective Availability in 2000 was proposed by the US Secretary of Defense, William Perry, because of the widespread growth of differential GPS services to improve civilian accuracy and eliminate the US military advantage. Sony VAIO PCG-7191L Battery Moreover, the US military was actively developing technologies to deny GPS service to potential adversaries on a regional basis.[15] Over the last decade, the U.S. has implemented several improvements to the GPS service, including new signals for civil use and increased accuracy and integrity for all users, all while maintaining compatibility with existing GPS equipment. Sony VAIO PCG-3C1M Battery GPS modernization[16] has now become an ongoing initiative to upgrade the Global Positioning System with new capabilities to meet growing military, civil, and commercial needs. The program is being implemented through a series of satellite acquisitions, including GPS Block III and the Next Generation Operational Control System (OCX). Sony VAIO PCG-3F1M Battery The U.S. Government continues to improve the GPS space and ground segments to increase performance and accuracy. GPS is owned and operated by the United States Government as a national resource. Department of Defense (DoD) is the steward of GPS. Interagency GPS Executive Board (IGEB) oversaw GPS policy matters from 1996 to 2004. Sony VAIO PCG-3H1M Battery After that the National Space-Based Positioning, Navigation and Timing Executive Committee was established by presidential directive in 2004 to advise and coordinate federal departments and agencies on matters concerning the GPS and related systems. The executive committee is chaired jointly by the deputy secretaries of defense and transportation. Sony VAIO PCG-3J1M Battery Its membership includes equivalent-level officials from the departments of state, commerce, and homeland security, the joint chiefs of staff, and NASA. Components of the executive office of the president participate as observers to the executive committee, and the FCC chairman participates as a liaison. Sony VAIO PCG-8141M Battery The DoD is required by law to "maintain a Standard Positioning Service (as defined in the federal radio navigation plan and the standard positioning service signal specification) that will be available on a continuous, worldwide basis," and "develop measures to prevent hostile use of GPS and its augmentations without unduly disrupting or degrading civilian uses." Sony VAIO PCG-8161M Battery
  • In 1972, the USAF Central Inertial Guidance Test Facility (Holloman AFB), conducted developmental flight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.
In 1978, the first experimental Block-I GPS satellite was launched. Sony VAIO PCG-3C2M Battery In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 that strayed into prohibited airspace because of navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that GPS would be made available for civilian uses once it was completed,although it had been previously published [in Navigation magazine] that the CA code (Coarse Acquisition code) would be available to civilian users. Sony VAIO PCG-5N2M Battery By 1985, ten more experimental Block-I satellites had been launched to validate the concept. Command & Control of these satellites had moved from Onizuka AFS, CA and turned over to the 2nd Satellite Control Squadron (2SCS) located at Falcon Air Force Station in Colorado Springs, Colorado.[21][22] Sony VAIO PCG-5P1M Battery
  • On February 14, 1989, the first modern Block-II satellite was launched.
  • The Gulf War from 1990 to 1991, was the first conflict where GPS was widely used.[23]
In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing. Sony VAIO PCG-5S1M Battery
  • By December 1993, GPS achieved initial operational capability (IOC), indicating a full constellation (24 satellites) was available and providing the Standard Positioning Service (SPS).[24]
Full Operational Capability (FOC) was declared by Air Force Space Command (AFSPC) in April 1995, signifying full availability of the military's secure Precise Positioning Service (PPS).[24] Sony VAIO PCG-9Z1M Battery In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive[25] declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset. Sony VAIO PCG-7171M Battery In 1998, United States Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety and in 2000 the United States Congress authorized the effort, referring to it as GPS III. Sony VAIO PCG-7186M Battery

On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded signal globally.

In 2004, the United States Government signed an agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system. Sony VAIO PCG-81112M Battery

In 2004, United States President George W. Bush updated the national policy and replaced the executive board with the National Executive Committee for Space-Based Positioning, Navigation, and Timing.[26]

November 2004, Qualcomm announced successful tests of assisted GPS for mobile phones.[27] Sony VAIO PCG-31311M Battery

In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.On September 14, 2007, the aging mainframe-based Ground Segment Control System was transferred to the new Architecture Evolution Plan.[28]

On May 19, 2009, the United States Government Accountability Office issued a report warning that some GPS satellites could fail as soon as 2010.[29] Sony VAIO PCG-8152M Battery

On May 21, 2009, the Air Force Space Command allayed fears of GPS failure saying "There's only a small risk we will not continue to exceed our performance standard."[30]

On January 11, 2010, an update of ground control systems caused a software incompatibility with 8000 to 10000 military receivers manufactured by a division of Trimble Navigation Limited of Sunnyvale, Calif.[31] Sony VAIO PCG-31111M Battery

On February 25, 2010,[32] the U.S. Air Force awarded the contract to develop the GPS Next Generation Operational Control System (OCX) to improve accuracy and availability of GPS navigation signals, and serve as a critical part of GPS modernization.

A GPS satellite was launched on May 28, 2010. Sony VAIO PCG-61111M Battery The oldest GPS satellite still in operation was launched on November 26, 1990, and became operational on December 10, 1990.The GPS satellite, GPS IIF-2, was launched on July 16, 2011 at 06:41 GMT from Space Launch Complex 37B at the Cape Canaveral Air Force Station.The GPS satellite, GPS IIF-3, was launched on October 4, 2012 at 12:10 GMT from Space Launch Complex 37B at the Cape Canaveral Air Force Station. Sony VAIO PCG-51112M Battery On February 10, 1993, the National Aeronautic Association selected the GPS Team as winners of the 1992 Robert J. Collier Trophy, the nation's most prestigious aviation award. This team combines researchers from the Naval Research Laboratory, the USAF, the Aerospace Corporation, Rockwell International Corporation, andIBM Federal Systems Company. Sony VAIO PCG-51211M Battery The citation honors them "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago." Two GPS developers received the National Academy of Engineering Charles Stark Draper Prize for 2003: Sony VAIO PCG-51212M Battery Ivan Getting, emeritus president of The Aerospace Corporation and an engineer at the Massachusetts Institute of Technology, established the basis for GPS, improving on the World War II land-based radio system called LORAN (Long-range Radio Aid to Navigation). Sony VAIO PCG-41111M Battery Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force. Parkinson served twenty-one years in the Air Force, from 1957 to 1978, and retired with the rank of colonel. Sony VAIO PCG-41111V Battery

GPS developer Roger L. Easton received the National Medal of Technology on February 13, 2006.[37]

In 1998, GPS technology was inducted into the Space Foundation Space Technology Hall of Fame.[38] Sony VAIO PCG-61412V Battery Francis X. Kane (Col. USAF, ret.) was inducted into the U.S. Air Force Space and Missile Pioneers Hall of Fame at Lackland A.F.B., San Antonio, Texas, March 2, 2010 for his role in space technology development and the engineering design concept of GPS conducted as part of Project 621B. Sony VAIO PCG-71112M Battery On October 4, 2011, the International Astronautical Federation (IAF) awarded the Global Positioning System (GPS) its 60th Anniversary Award, nominated by IAF member, the American Institute for Aeronautics and Astronautics (AIAA). The IAF Honors and Awards Committee recognized the uniqueness of the GPS program and the exemplary role it has played in building international collaboration for the benefit of humanity. Sony VAIO PCG-81111V Battery 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. Sony VAIO PCG-81111V Battery 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. Sony VAIO PCG-81212M Battery 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. In typical GPS operation, four or more satellites must be visible to obtain an accurate result. Sony VAIO PCG-81212V Battery Four sphere surfaces typically do not intersect. [a] Because of this we can say with confidence that when we solve the navigation equations to find an intersection, this solution gives us the position of the receiver along with accurate time thereby eliminating the need for a very large, expensive, and power hungry clock. Sony VAIO PCG-51111M Battery The very accurately computed time is used only for display or not at all in many GPS applications, which use only the location. A number of applications for GPS do make use of this cheap and highly accurate timing. These include time transfer, traffic signal timing, and synchronization of cell phone base stations. Sony VAIO VPCS13X9E/B battery Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. For example, a ship or aircraft may have known elevation. Some GPS receivers may use additional clues or assumptions such as reusing the last known altitudeSony VAIO VPCS12V9E/B battery , dead reckoning, inertial navigation, or including information from the vehicle computer, to give a (possibly degraded) position when fewer than four satellites are visible.[39][40][41] The current GPS consists of three major segments. These are the space segment (SS), a control segment (CS), and a user segment (US). Sony VAIO VPCS12V9E/B battery 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.[43] Sony VAIO VPCF13M8E/B battery 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. Sony VAIO VPCF13Z0E/B battery The user segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service, and tens of millions of civil, commercial, and scientific users of the Standard Positioning Service (see GPS navigation devices). The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. Sony VAIO VPCM13M1E/L battery The GPS design originally called for 24 SVs, eight each in three approximately circular orbits,[44] but this was modified to six orbital planes with four satellites each.[45] The orbits are centered on the Earth, not rotating with the Earth, but instead fixed with respect to the distant stars.[46] Sony VAIO VPCM13M1E/W battery The six orbit planes have approximately 55° inclination (tilt relative to Earth'sequator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).[47] The orbital period is one-half a sidereal day, i.e., 11 hours and 58 minutes.[48] Sony VAIO VPCF22M1E battery The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.[49]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. Sony VAIO VPCF11M1E/H battery Orbiting at an altitude of approximately 20,200 km (12,600 mi); orbital radius of approximately 26,600 km (16,500 mi), each SV makes two complete orbits each sidereal day, repeating the same ground track each day.[50] This was very helpful during development because even with only four satellites, Sony VAIO VPCF13M0E/B battery correct alignment means all four are visible from one spot for a few hours each day. For military operations, the ground track repeat can be used to ensure good coverage in combat zones. As of December 2012,[51] there are 32 satellites in the GPS constellation. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. Sony VAIO VPCYB2M1E battery With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.[52] About nine satellites are visible from any point on the ground at any one time (see animation at right), Sony VAIO VPCYB3V1E battery ensuring considerable redundancy over the minimum four satellites needed for a position. The MCS can also access U.S. Air Force Satellite Control Network (AFSCN) ground antennas (for additional command and control capability) and NGA (National Geospatial-Intelligence Agency) monitor stations. Sony VAIO VPCY11M1E battery The flight paths of the satellites are tracked by dedicated U.S. Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs, Colorado and Cape Canaveral, along with shared NGA monitor stations operated in England, Argentina, Ecuador, Bahrain, Australia and Washington DC.[53] Sony VAIO VPCS12L9E/B battery The tracking information is sent to the Air Force Space Command MCS at Schriever Air Force Base 25 km (16 mi) ESE of Colorado Springs, which is operated by the 2nd Space Operations Squadron (2 SOPS) of the U.S. Air Force. Then 2 SOPS contacts each GPS satellite regularly with a navigational update using dedicated or shared (AFSCN) ground antennas Sony VAIO VPCF11S1E/B battery (GPS dedicated ground antennas are located at Kwajalein, Ascension Island, Diego Garcia, and Cape Canaveral). These updates synchronize the atomic clocks on board the satellites to within a few nanoseconds of each other, and adjust the ephemeris of each satellite's internal orbital model. Sony VAIO VPCYB3V1E/R Battery The updates are created by a Kalman filter that uses inputs from the ground monitoring stations, space weather information, and various other inputs.[54] Satellite maneuvers are not precise by GPS standards. So to change the orbit of a satellite, the satellite must be marked unhealthy, so receivers will not use it in their calculation. Sony VAIO VPCF23P1E Battery Then the maneuver can be carried out, and the resulting orbit tracked from the ground. Then the new ephemeris is uploaded and the satellite marked healthy again. The Operation Control Segment (OCS) currently serves as the control segment of record. It provides the operational capability that supports global GPS users and keeps the GPS system operational and performing within specification. Sony VAIO VPCF23N1E Battery OCS successfully replaced the legacy 1970’s-era mainframe computer at Schriever Air Force Base in September 2007. After installation, the system helped enable upgrades and provide a foundation for a new security architecture that supported the U.S. armed forces. OCS will continue to be the ground control system of record until the new segment, Sony VAIO VPCY21S1E/L Battery Next Generation GPS Operation Control System[2] (OCX), is fully developed and functional. The new capabilities provided by OCX will be the cornerstone for revolutionizing GPS’s mission capabilities, and enabling[55] Air Force Space Command to greatly enhance GPS operational services to U.S. combat forces, civil partners and myriad of domestic and international users. Sony VAIO VPCY21S1E/G battery The GPS OCX program also will reduce cost, schedule and technical risk. It is designed to provide 50%[56] sustainment cost savings through efficient software architecture and Performance-Based Logistics. In addition, GPS OCX expected to cost millions less than the cost to upgrade OCS while providing four times the capability. Sony VAIO VPCF24M1E battery The GPS OCX program represents a critical part of GPS modernization and provides significant information assurance improvements over the current GPS OCS program.OCX will have the ability to control and manage GPS legacy satellites as well as the next generation of GPS III satellites, while enabling the full array of military signals. Sony VAIO VGN-AW110J/H Battery

Built on a flexible architecture that can rapidly adapt to the changing needs of today’s and future GPS users allowing immediate access to GPS data and constellations status through secure, accurate and reliable information.

Empowers the warfighter with more secure, actionable and predictive information to enhance situational awareness. Sony VAIO VGN-SR11M Battery

Enables new modernized signals (L1C, L2C, and L5) and has M-code capability, which the legacy system is unable to do.

Provides significant information assurance improvements over the current program including detecting and preventing cyber attacks, while isolating, containing and operating during such attacks. Sony VAIO VGN-SR11MR Battery

Supports higher volume near real-time command and control capabilities.

On September 14, 2011,[57] the U.S. Air Force announced the completion of GPS OCX Preliminary Design Review and confirmed that the OCX program is ready for the next phase of development.

The GPS OCX program has achieved major milestones and is on track to support the GPS IIIA launch in May 2014. Sony VAIO VGN-SR140D Battery

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