Executive positions and advisory positions that require knowledge of air defense. AIR AND MISSILE DEFENSE IN RELATION TO ARMY TENETS. Air and missile defense operations are inherently joint operations, multi. Little warning for maneuver forces and their short-range hamper engagement. Transportation sounds - sounds of vehicles for kids - This video has a set of different modes of transportation that babies, toddlers, preschoolers, kindergarten kids.

A runs through a checklist during Global Positioning System satellite operations. The Global Positioning System ( GPS), originally Navstar GPS, is a space-based system owned by the government and operated by the. It is a that provides and time information to a anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The GPS does not require the user to transmit any data, and it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military, civil, and commercial users around the world.

The United States government created the system, maintains it, and makes it freely accessible to anyone with a The GPS project was launched by the in 1973 for use by the United States military and became fully operational in 1995. It was allowed for civilian use in the 1980s. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of satellites and Next Generation Operational Control System (OCX). Announcements from Vice President and the in 1998 initiated these changes. In 2000, the authorized the modernization effort,. In addition to GPS, other systems are in use or under development, mainly because the US government can selectively deny access to the system, as happened to the Indian military in 1999 during the, or degrade the service at any time. The Russian Global Navigation Satellite System () was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s.

GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, to within two meters. There are also the European Union, China's, India's and Japan's.

Contents • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • History [ ] The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including a number of classified engineering design studies from the 1960s. The developed the system, which originally used 24 satellites. It was initially developed for use by the United States military and became fully operational in 1995. It was allowed for civilian use in the 1980s.

Of the, of, and of the are credited with inventing it. The design of GPS is based partly on similar ground-based systems, such as and the, developed in the early 1940s and used by the British Royal Navy during. Proposed a test of — detecting time slowing in a strong field using accurate placed in orbit inside artificial satellites. And predict that the clocks on the GPS satellites would be seen by the Earth's observers to run 38 microseconds faster per day than the clocks on the Earth.

The GPS calculated positions would quickly drift into error, accumulating to 10 kilometers per day. This was corrected for in the design of GPS. Predecessors [ ] When the launched the first artificial satellite ( 1) in 1957, two American physicists, and, at Johns Hopkins University's (APL) decided to monitor its radio transmissions. Within hours they realized that, because of the, they could pinpoint where the satellite was along its orbit. The Director of the APL gave them access to their to do the heavy calculations required. The next spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the user's location, given that of the satellite. (At the time, the Navy was developing the submarine-launched missile, which required them to know the submarine's location.) This led them and APL to develop the system.

In 1959, ARPA (renamed in 1972) also played a role in TRANSIT. Emblem of the The first satellite navigation system, TRANSIT, used by the, was first successfully tested in 1960. It used a of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the satellite, which proved the feasibility of placing accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based navigation system, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy.

While there were wide needs for accurate navigation in military and civilian sectors, almost none of those was seen as justification for the billions of dollars it would cost in research, development, deployment, and operation for a constellation of navigation satellites. During the, 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 consisted of the United States Navy's (SLBMs) along with (USAF) and (ICBMs). Considered vital to the posture, accurate determination of the SLBM launch position was a. Precise navigation would enable United States to get an accurate fix of their positions before they launched their SLBMs.

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, there was a proposal to use mobile launch platforms (comparable to the Russian and ) 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. A follow-on study, 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' and promised increased accuracy for Air Force bombers as well as ICBMs.

Updates from the Navy TRANSIT system were too slow for the high speeds of Air Force operation. The Naval 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. Another important predecessor to GPS came from a different branch of the United States military. In 1964, the orbited its first 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. 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. Decades later, during the early years of GPS, civilian surveying became one of the first fields to make use of the new technology, because surveyors 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. Development [ ] 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 twelve military officers at the Pentagon discussed the creation of a Defense Navigation Satellite System (DNSS). It was at this meeting that the real synthesis that became GPS was created. Later that year, the DNSS program was named Navstar, or Navigation System Using Timing and Ranging. 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. Ten ' prototype satellites were launched between 1978 and 1985 (an additional unit was destroyed in a launch failure). The effects of the ionosphere on radio transmission through the ionosphere was investigated within a geophysics laboratory of Air Force Cambridge Research Laboratory.

Located at, outside Boston, the lab was renamed the Air Force Geophysical Research Lab (AFGRL) in 1974. AFGRL developed the Klobuchar Model for computing ionospheric corrections to GPS location.

Of note is work done by Australian Space Scientist Elizabeth Essex-Cohen at AFGRL in 1974. She was concerned with the curving of the path of radio waves traversing the ionosphere from NavSTAR satellites. After, a carrying 269 people, was shot down in 1983 after straying into the USSR's, in the vicinity of and, President issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good. The first Block II satellite was launched on February 14, 1989, and the 24th satellite was launched in 1994. The GPS program cost at this point, not including the cost of the user equipment, but including the costs of the satellite launches, has been estimated at about USD 5 billion (then-year dollars).

Initially, the highest quality signal was reserved for military use, and the signal available for civilian use was intentionally degraded (). This changed with President signing a policy directive to turn off Selective Availability May 1, 2000 to provide the same accuracy to civilians that was afforded to the military. The directive was proposed by the U.S. Secretary of Defense,, because of the widespread growth of services to improve civilian accuracy and eliminate the U.S.

Military advantage. Moreover, the U.S. Military was actively developing technologies to deny GPS service to potential adversaries on a regional basis. Since its deployment, 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 the while maintaining compatibility with existing GPS equipment. Modernization of the satellite system has been an ongoing initiative by the U.S. Department of Defense through a series of to meet the growing needs of the military, civilians, and the commercial market. As of early 2015, high-quality, grade, Standard Positioning Service (SPS) GPS receivers provide horizontal accuracy of better than 3. Win Myanmar Fonts Systems Of Linear here. 5 meters, although many factors such as receiver quality and atmospheric issues can affect this accuracy.

GPS is owned and operated by the United States government as a national resource. The Department of Defense is the steward of GPS. The Interagency GPS Executive Board (IGEB) oversaw GPS policy matters from 1996 to 2004.

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.

Its membership includes equivalent-level officials from the Departments of State, Commerce, and Homeland Security, the and. Components of the executive office of the president participate as observers to the executive committee, and the FCC chairman participates as a liaison. Department of Defense 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.' Timeline and modernization [ ].

This section needs additional citations for. Unsourced material may be challenged and removed. (March 2015) () Fundamentals [ ] The GPS concept is based on time and the known position of GPS specialized. The satellites carry very stable that are synchronized with one another and with the ground clocks. Any drift from true time maintained on the ground is corrected daily. In the same manner, the satellite locations are known with great precision. GPS receivers have clocks as well, but they are less stable and less precise.

GPS satellites continuously transmit data about their current time and position. A GPS receiver monitors multiple satellites and solves equations to determine the precise position of the receiver and its deviation from true time.

At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time). More detailed description [ ] Each GPS satellite continually broadcasts a signal ( with ) that includes: • A pseudorandom code (sequence of ones and zeros) that is known to the receiver. By time-aligning a receiver-generated version and the receiver-measured version of the code, the time of arrival (TOA) of a defined point in the code sequence, called an epoch, can be found in the receiver clock time scale • A message that includes the time of transmission (TOT) of the code epoch (in GPS time scale) and the satellite position at that time Conceptually, the receiver measures the TOAs (according to its own clock) of four satellite signals.

From the TOAs and the TOTs, the receiver forms four (TOF) values, which are (given the speed of light) approximately equivalent to receiver-satellite ranges. The receiver then computes its three-dimensional position and clock deviation from the four TOFs. In practice the receiver position (in three dimensional with origin at the Earth's center) and the offset of the receiver clock relative to the GPS time are computed simultaneously, using the to process the TOFs.

The receiver's Earth-centered solution location is usually converted to, and height relative to an ellipsoidal Earth model. The height may then be further converted to height relative to the (e.g., ) (essentially, mean ).

These coordinates may be displayed, e.g., on a, and/or recorded and/or used by some other system (e.g., a vehicle guidance system). User-satellite geometry [ ] Although usually not formed explicitly in the receiver processing, the conceptual time differences of arrival (TDOAs) define the measurement geometry. Each TDOA corresponds to a of revolution (see ).

The line connecting the two satellites involved (and its extensions) forms the axis of the hyperboloid. The receiver is located at the point where three hyperboloids intersect. It is sometimes incorrectly said that the user location is at the intersection of three spheres. While simpler to visualize, this is only the case if the receiver has a clock synchronized with the satellite clocks (i.e., the receiver measures true ranges to the satellites rather than range differences).

There are significant performance benefits to the user carrying a clock synchronized with the satellites. Foremost is that only three satellites are needed to compute a position solution. If this were part of the GPS concept so that all users needed to carry a synchronized clock, then a smaller number of satellites could be deployed. However, the cost and complexity of the user equipment would increase significantly.

Receiver in continuous operation [ ] The description above is representative of a receiver start-up situation. Most receivers have a, sometimes called a tracker, that combines sets of satellite measurements collected at different times—in effect, taking advantage of the fact that successive receiver positions are usually close to each other.

After a set of measurements are processed, the tracker predicts the receiver location corresponding to the next set of satellite measurements. When the new measurements are collected, the receiver uses a weighting scheme to combine the new measurements with the tracker prediction. In general, a tracker can (a) improve receiver position and time accuracy, (b) reject bad measurements, and (c) estimate receiver speed and direction.

The disadvantage of a tracker is that changes in speed or direction can only be computed with a delay, and that derived direction becomes inaccurate when the distance traveled between two position measurements drops below or near the of position measurement. GPS units can use measurements of the of the signals received to compute velocity accurately. More advanced navigation systems use additional sensors like a or an to complement GPS. Non-navigation applications [ ]. For a list of applications, see. In typical GPS operation as a navigator, four or more satellites must be visible to obtain an accurate result.

The solution of the gives the position of the receiver along with the difference between the time kept by the receiver's on-board clock and the true time-of-day, thereby eliminating the need for a more precise and possibly impractical receiver based clock. Applications for GPS such as, traffic signal timing, and, make use of this cheap and highly accurate timing. Some GPS applications use this time for display, or, other than for the basic position calculations, do not use it at all. 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,,, or including information from the vehicle computer, to give a (possibly degraded) position when fewer than four satellites are visible. Structure [ ]. This section needs additional citations for. Unsourced material may be challenged and removed. (March 2015) () The current GPS consists of three major segments.

These are the space segment, a control segment, and a user segment. Air Force develops, maintains, and operates the space and control segments. GPS satellites from space, and each GPS receiver uses these signals to calculate its three-dimensional location (latitude, longitude, and altitude) and the current time. Space segment [ ]. A visual example of a 24 satellite GPS constellation in motion with the earth rotating.

Notice how the number of satellites in view from a given point on the earth's surface, in this example in Golden, Colorado, USA(39.7469° N, 105.2108° W), changes with time. The space segment (SS) is composed of 24 to 32 satellites in and also includes the payload adapters to the boosters required to launch them into orbit. The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance.

The GPS design originally called for 24 SVs, eight each in three approximately circular, but this was modified to six orbital planes with four satellites each. The six orbit planes have approximately 55° (tilt relative to the Earth's ) and are separated by 60° of the (angle along the equator from a reference point to the orbit's intersection). The orbital is one-half a, i.e., 11 hours and 58 minutes so that the satellites pass over the same locations or almost the same locations every day. The orbits are arranged so that at least six satellites are always within from almost everywhere on the Earth's surface.

The result of this objective is that the four satellites are not evenly spaced (90°) apart within each orbit. In general terms, the angular difference between satellites in each orbit is 30°, 105°, 120°, and 105° apart, which sum to 360°.

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, repeating the same each day. This was very helpful during development because even with only four satellites, 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 February 2016, there are 32 satellites in the GPS, 31 of which are in use. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. 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. About nine satellites are visible from any point on the ground at any one time (see animation at right), ensuring considerable redundancy over the minimum four satellites needed for a position. Control segment [ ]. Ground monitor station used from 1984 to 2007, on display at the. The control segment (CS) is composed of: • a master control station (MCS), • an alternate master control station, • four dedicated ground antennas, and • six dedicated monitor stations. The MCS can also access U.S.

Air Force Satellite Control Network (AFSCN) ground antennas (for additional command and control capability) and NGA () monitor stations. The flight paths of the satellites are tracked by dedicated U.S. Air Force monitoring stations in,,,, and, along with shared NGA monitor stations operated in England, Argentina, Ecuador, Bahrain, Australia and Washington DC. The tracking information is sent to the Air Force Space Command MCS at 25 km (16 mi) ESE of Colorado Springs, which is operated by the (2 SOPS) of the U.S. Then 2 SOPS contacts each GPS satellite regularly with a navigational update using dedicated or shared (AFSCN) ground antennas (GPS dedicated ground antennas are located at,,, and ). These updates synchronize the atomic clocks on board the satellites to within a few of each other, and adjust the of each satellite's internal orbital model. The updates are created by a that uses inputs from the ground monitoring stations, information, and various other inputs.

Satellite maneuvers are not precise by GPS standards—so to change a satellite's orbit, the satellite must be marked unhealthy, so receivers don't use it. After the satellite maneuver, engineers track the new orbit from the ground, upload the new ephemeris, and mark the satellite healthy again.

The operation control segment (OCS) currently serves as the control segment of record. It provides the operational capability that supports GPS users and keeps the GPS operational and performing within specification.

OCS successfully replaced the legacy 1970s-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 U.S.

Armed forces. OCS will continue to be the ground control system of record until the new segment, Next Generation GPS Operation Control System (OCX), is fully developed and functional. The new capabilities provided by OCX will be the cornerstone for revolutionizing GPS's mission capabilities, enabling Air Force Space Command to greatly enhance GPS operational services to U.S. Combat forces, civil partners and myriad domestic and international users. The GPS OCX program also will reduce cost, schedule and technical risk.

It is designed to provide 50% sustainment cost savings through efficient software architecture and Performance-Based Logistics. In addition, GPS OCX is expected to cost millions less than the cost to upgrade OCS while providing four times the capability. 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. • 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 constellation status through secure, accurate and reliable information.

• Provides the warfighter with more secure, actionable and predictive information to enhance situational awareness. • 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. • Supports higher volume near real-time command and control capabilities and abilities. On September 14, 2011, 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 missed major milestones and is pushing the launch beyond April 2016. User segment [ ]. The first portable GPS unit, Leica WM 101 displayed at the Irish National Science Museum at Maynooth. The user segment (US) 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 ). In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly stable clock (often a ).

They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, as of 2007, receivers typically have between 12 and 20 channels. Though there are many receiver manufacturers, they almost all use one of the chipsets produced for this purpose.

A typical GPS receiver with integrated antenna. Many GPS receivers can relay position data to a PC or other device using the protocol. Although this protocol is officially defined by the National Marine Electronics Association (NMEA), references to this protocol have been compiled from public records, allowing open source tools like to read the protocol without violating laws.

[ ] Other proprietary protocols exist as well, such as the and protocols. Receivers can interface with other devices using methods including a serial connection,,. Applications [ ]. This is mounted on the roof of a hut containing a scientific experiment needing precise timing. Many civilian applications use one or more of GPS's three basic components: absolute location, relative movement, and time transfer. •: GPS has made a great evolution in different aspects of modern agricultural sectors. Today, a growing number of crop producers are using GPS and other modern electronic and computer equipment to practice Site Specific Management (SSM) and precision agriculture.

This technology has the potential in agricultural mechanization (farm and machinery management) by providing farmers with a sophisticated tool to measure yield on much smaller scales as well as precise determination and automatic storing of variables such as field time, working area, machine travel distance and speed, fuel consumption and yield information. •: both positional and data is used in and. GPS is also used in both with as well as by professional observatories for finding. •: applying location and routes for cars and trucks to function without a human driver. •: both civilian and military cartographers use GPS extensively. •: clock synchronization enables time transfer, which is critical for synchronizing its spreading codes with other base stations to facilitate inter-cell handoff and support hybrid GPS/cellular position detection for and other applications.

The first launched in the late 1990s. (FCC) mandated the feature in either the handset or in the towers (for use in triangulation) in 2002 so emergency services could locate 911 callers. Third-party software developers later gained access to GPS APIs from upon launch, followed by in 2006, and soon thereafter. •: the accuracy of GPS time signals (±10 ns) is second only to the atomic clocks they are based on, and is used in applications such as.

• /: many emergency services depend upon GPS for location and timing capabilities. • GPS-equipped and: measure and calculate the atmospheric pressure, wind speed and direction up to 27 km from the Earth's surface. • for weather and atmospheric science applications. •: used to identify, locate and maintain contact reports with one or more vehicles in real-time. •:,, and systems use GPS to locate devices that are attached to or carried by a person, vehicle, or pet. The application can provide continuous tracking and send notifications if the target leaves a designated (or 'fenced-in') area.

•: applies location coordinates to digital objects such as photographs (in data) and other documents for purposes such as creating map overlays with devices like • •: the use of RTK GPS has significantly improved several mining operations such as drilling, shoveling, vehicle tracking, and surveying. RTK GPS provides centimeter-level positioning accuracy. •: It is possible to aggregate GPS data from multiple users to understand movement patterns, common trajectories and interesting locations. •: location determines what content to display; for instance, information about an approaching point of interest.

•: navigators value digitally precise velocity and orientation measurements. •: GPS enables highly accurate timestamping of power system measurements, making it possible to compute. •: for example,,,,, and other kinds of. •: self-navigating, autonomous robots using a GPS sensors, which calculate latitude, longitude, time, speed, and heading. •: used in football and rugby for the control and analysis of the training load.

•: surveyors use absolute locations to make maps and determine property boundaries. •: GPS enables direct fault motion measurement of. Between earthquakes GPS can be used to measure motion and deformation to estimate seismic strain buildup for creating maps. •: GPS technology integrated with computers and mobile communications technology in. Restrictions on civilian use [ ] The U.S. Government controls the export of some civilian receivers. All GPS receivers capable of functioning above 18 km (60,000 feet) altitude and 515 m/s (1,000 knots), or designed or modified for use with unmanned air vehicles like, e.g., ballistic or cruise missile systems, are classified as (weapons)—which means they require export licenses.

This rule applies even to otherwise purely civilian units that only receive the L1 frequency and the C/A (Coarse/Acquisition) code. Disabling operation above these limits exempts the receiver from classification as a munition. Vendor interpretations differ.

The rule refers to operation at both the target altitude and speed, but some receivers stop operating even when stationary. This has caused problems with some amateur radio balloon launches that regularly reach 30 km (100,000 feet). These limits only apply to units or components exported from the USA.

A growing trade in various components exists, including GPS units from other countries. These are expressly sold as -free. Military [ ]. As of 2009, military GPS applications include: • Navigation: Soldiers use GPS to find objectives, even in the dark or in unfamiliar territory, and to coordinate troop and supply movement. In the United States armed forces, commanders use the Commander's Digital Assistant and lower ranks use the Soldier Digital Assistant.

• Target tracking: Various military weapons systems use GPS to track potential ground and air targets before flagging them as hostile. [ ] These weapon systems pass target coordinates to to allow them to engage targets accurately. Military aircraft, particularly in roles, use GPS to find targets. • Missile and projectile guidance: GPS allows accurate targeting of various military weapons including,, and. We No Speak Americano Full Song Download. Embedded GPS receivers able to withstand accelerations of 12,000 g or about 118 km/s 2 have been developed for use in 155-millimeter (6.1 in) shells.

• Search and rescue. • Reconnaissance: Patrol movement can be managed more closely. • GPS satellites carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an electromagnetic pulse (EMP) sensor (W-sensor), that form a major portion of the. General William Shelton has stated that future satellites may drop this feature to save money. GPS type navigation was first used in war in the, before GPS was fully developed in 1995, to assist to navigate and perform maneuvers in the war. The war also demonstrated the vulnerability of GPS to being, when Iraqi forces installed jamming devices on likely targets that emitted radio noise, disrupting reception of the weak GPS signal.

Communication [ ]. Main article: The navigational signals transmitted by GPS satellites encode a variety of information including satellite positions, the state of the internal clocks, and the health of the network. These signals are transmitted on two separate carrier frequencies that are common to all satellites in the network. Two different encodings are used: a public encoding that enables lower resolution navigation, and an encrypted encoding used by the U.S. Message format [ ] GPS message format Subframes Description 1 Satellite clock, GPS time relationship 2–3 Ephemeris (precise satellite orbit) 4–5 Almanac component (satellite network synopsis, error correction) Each GPS satellite continuously broadcasts a navigation message on L1 (C/A and P/Y) and L2 (P/Y) frequencies at a rate of 50 bits per second (see ).

Each complete message takes 750 seconds (12 1/2 minutes) to complete. The message structure has a basic format of a 1500-bit-long frame made up of five subframes, each subframe being 300 bits (6 seconds) long. Subframes 4 and 5 are 25 times each, so that a complete data message requires the transmission of 25 full frames. Each subframe consists of ten words, each 30 bits long. Thus, with 300 bits in a subframe times 5 subframes in a frame times 25 frames in a message, each message is 37,500 bits long.

At a transmission rate of 50-bit/s, this gives 750 seconds to transmit an entire. Each 30-second frame begins precisely on the minute or half-minute as indicated by the atomic clock on each satellite. The first subframe of each frame encodes the week number and the time within the week, as well as the data about the health of the satellite.

The second and the third subframes contain the – the precise orbit for the satellite. The fourth and fifth subframes contain the almanac, which contains coarse orbit and status information for up to 32 satellites in the constellation as well as data related to error correction.

Thus, to obtain an accurate satellite location from this transmitted message, the receiver must demodulate the message from each satellite it includes in its solution for 18 to 30 seconds. To collect all transmitted almanacs, the receiver must demodulate the message for 732 to 750 seconds or 12 1/2 minutes. All satellites broadcast at the same frequencies, encoding signals using unique (CDMA) so receivers can distinguish individual satellites from each other. The system uses two distinct CDMA encoding types: the coarse/acquisition (C/A) code, which is accessible by the general public, and the precise (P(Y)) code, which is encrypted so that only the U.S.

Military and other NATO nations who have been given access to the encryption code can access it. The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for updates every 6 hours or longer in non-nominal conditions. The almanac is updated typically every 24 hours. Additionally, data for a few weeks following is uploaded in case of transmission updates that delay data upload.

[ ] Satellite frequencies [ ] GPS frequency overview: 607 Band Frequency Description L1 1575.42 MHz Coarse-acquisition (C/A) and encrypted precision (P(Y)) codes, plus the L1 civilian () and military (M) codes on future Block III satellites. L2 1227.60 MHz P(Y) code, plus the and military codes on the Block IIR-M and newer satellites. L3 1381.05 MHz Used for nuclear detonation (NUDET) detection. L4 1379.913 MHz Being studied for additional ionospheric correction. L5 1176.45 MHz Proposed for use as a civilian safety-of-life (SoL) signal. All satellites broadcast at the same two frequencies, 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal). The satellite network uses a CDMA spread-spectrum technique: 607 where the low-bitrate message data is encoded with a high-rate (PRN) sequence that is different for each satellite.

The receiver must be aware of the PRN codes for each satellite to reconstruct the actual message data. The C/A code, for civilian use, transmits data at 1.023 million per second, whereas the P code, for U.S. Military use, transmits at 10.23 million chips per second. The actual internal reference of the satellites is 9543 MHz to compensate for that make observers on the Earth perceive a different time reference with respect to the transmitters in orbit.

The L1 carrier is modulated by both the C/A and P codes, while the L2 carrier is only modulated by the P code. The P code can be encrypted as a so-called P(Y) code that is only available to military equipment with a proper decryption key. Both the C/A and P(Y) codes impart the precise time-of-day to the user. The L3 signal at a frequency of 1.38105 GHz is used to transmit data from the satellites to ground stations. This data is used by the United States Nuclear Detonation (NUDET) Detection System (USNDS) to detect, locate, and report nuclear detonations (NUDETs) in the Earth's atmosphere and near space.

One usage is the enforcement of nuclear test ban treaties. The L4 band at 1.379913 GHz is being studied for additional ionospheric correction.: 607 The L5 frequency band at 1.17645 GHz was added in the process of. This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances. The first Block IIF satellite that provides this signal was launched in 2010. The L5 consists of two carrier components that are in phase quadrature with each other.

Each carrier component is bi-phase shift key (BPSK) modulated by a separate bit train. 'L5, the third civil GPS signal, will eventually support safety-of-life applications for aviation and provide improved availability and accuracy.'

In 2011, a conditional waiver was granted to to operate a terrestrial broadband service near the L1 band. Although LightSquared had applied for a license to operate in the 1525 to 1559 band as early as 2003 and it was put out for public comment, the FCC asked LightSquared to form a study group with the GPS community to test GPS receivers and identify issue that might arise due to the larger signal power from the LightSquared terrestrial network. The GPS community had not objected to the LightSquared (formerly MSV and SkyTerra) applications until November 2010, when LightSquared applied for a modification to its Ancillary Terrestrial Component (ATC) authorization. This filing (SAT-MOD-2019) amounted to a request to run several orders of magnitude more power in the same frequency band for terrestrial base stations, essentially repurposing what was supposed to be a 'quiet neighborhood' for signals from space as the equivalent of a cellular network.

Testing in the first half of 2011 has demonstrated that the impact of the lower 10 MHz of spectrum is minimal to GPS devices (less than 1% of the total GPS devices are affected). The upper 10 MHz intended for use by LightSquared may have some impact on GPS devices. There is some concern that this may seriously degrade the GPS signal for many consumer uses. Magazine reports that the latest testing (June 2011) confirms 'significant jamming' of GPS by LightSquared's system. Demodulation and decoding [ ]. Demodulating and Decoding GPS Satellite Signals using the Coarse/Acquisition.

Because all of the satellite signals are modulated onto the same L1 carrier frequency, the signals must be separated after demodulation. This is done by assigning each satellite a unique binary known as a. The signals are decoded after demodulation using addition of the Gold codes corresponding to the satellites monitored by the receiver. If the almanac information has previously been acquired, the receiver picks the satellites to listen for by their PRNs, unique numbers in the range 1 through 32. If the almanac information is not in memory, the receiver enters a search mode until a lock is obtained on one of the satellites. To obtain a lock, it is necessary that there be an unobstructed line of sight from the receiver to the satellite. The receiver can then acquire the almanac and determine the satellites it should listen for.

As it detects each satellite's signal, it identifies it by its distinct C/A code pattern. There can be a delay of up to 30 seconds before the first estimate of position because of the need to read the ephemeris data. Processing of the navigation message enables the determination of the time of transmission and the satellite position at this time. For more information see. Navigation equations [ ].

Main article: GPS error analysis examines error sources in GPS results and the expected size of those errors. GPS makes corrections for receiver clock errors and other effects, but some residual errors remain uncorrected. Error sources include signal arrival time measurements, numerical calculations, atmospheric effects (ionospheric/tropospheric delays), and clock data, multipath signals, and natural and artificial interference. Magnitude of residual errors from these sources depends on geometric dilution of precision. Artificial errors may result from jamming devices and threaten ships and aircraft or from intentional signal degradation through selective availability, which limited accuracy to ≈6–12 m, but has been switched off since May 1, 2000. Accuracy enhancement and surveying [ ]. Comparison of,,,,,, and orbits, with the and the to scale.

The 's orbit is around 9 times larger than geostationary orbit. (In hover over an orbit or its label to highlight it; click to load its article.) Other satellite navigation systems in use or various states of development include: • – global navigation system. Fully operational worldwide. • – a global system being developed by the and other partner countries, which began operation in 2016, and is expected to be fully deployed by 2020. • – regional system, currently limited to Asia and the West Pacific, global coverage planned to be operational by 2020 • - A regional navigation system developed by the. • - A regional navigation system in development that would be receivable within. See also [ ] • • • • • • • • • • • • • Notes [ ].