Gps satellite


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GPS Satellites :: Radio-Electronics.Com

- summary or overview of the GPS satellites, the satellite orbits, and function of the satellites themselves.

The GPS satellites form the basis of the overall global positioning system. Their development took place over many years, and they presented many technical challenges in terms of obtaining the correct level of accuracy.

Several blocks of GPS satellites have been launched over the years, each set providing updates to the previous ones as the system has been progressively updated.

GPS satellite basics

The GPS satellites have been under constant improvement since the first ones were launched in 1978. Although the first satellite was launched in 1978, it took until 1994 before a full constellation of 24 satellites was achieved.

Each satellite is built to last approximately 10 years, although the detail below show this varies considerably according to the different phases. This lifetime is not governed so much by the reliability of the electronics, but more by other actors such as battery life and the amount of fuel that can be carried for keeping the satellite exactly in the right orbit and travelling at the required velocity.

Each GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended. The transmitter power of a satellite is about 50 watts or less.

Satellite Block Launch Period Successful Launches Design Lifeyears Launch Mass(kg) DimensionsH x W x L (cm)
I 1978 - 1985 10 5 759  
II 1989 - 1990 9 7.5 1660  
IIA 1990 - 1997 19 7.5 1816  
IIR 1997 - 2004 12 10 2032 152 x 193 x 191
IIR-M 2005 - 2009 8      
IIF 2010 - 2011 1 (11 in prep) 15   244 x 197 x 197
IIIA 2014 onwards 12 planned      
Summary of GPS Satellites

GPS satellite orbits

The GPS satellites orbit the earth in a Medium Earth Orbit, MEO. The mean distance from the centre of the Earth is 26560 km (the mean radius of the Earth is 6360 km) and this means that the orbit altitude of the satellites is around 20 200 km.

The GPS satellites travel with a speed of about 3.9 km /s relative to the Earth as a whole, as opposed to relative to a fixed point on its surface. They have an orbit time of 12 hours (sidereal time) which equates to about 11 hours 58 minutes "Earth" time. This means that each satellite reaches a given position four minutes earlier each day (as it orbits the earth twice a day).

The satellite orbits are arranged on six planes. The inclination of the angles of the planes towards the equator is 55° and these planes are rotated by 60° against each other. This gives complete coverage of the globe. This means that the orbits range from 55° north to 55° degrees south. It is worth noting that Block I satellites had an inclination of 63° against the equator.

GPS satellite orbits

Within each orbit, there are at least four satellites. The system was designed for four satellites in each slot, but additional satellites are in orbit to act as "hot" spares in case of failure. In this way, when a satellite fails, and other one can be quickly put into its position to fill the gap.

Inclination of GPS satellite planes

The arrangement of the inclination of the satellite orbits at 55° to the equator has been decided upon to avoid too many satellites being over the polar regions at any time. The orbits run far enough north and south to ensure sufficient polar coverage. However it also ensures improved coverage in areas where there are more users.

GPS satellite orbit angles

An additional advantage is that it provides for a more stable constellation - factors disturbing orbits like the solar wind and gravitation fields have almost equal effects on all of the satellites using this arrangement.

The disadvantage for the polar regions is that at no time are any satellites directly above the users. This can lead to a small but predictable loss of precision.

By Ian Poole

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Satelite.Com GPS Satellites

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

How it works

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.

A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.

How accurate is GPS?

Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Garmin's 12 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters on average.

Newer Garmin GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average. No additional equipment or fees are required to take advantage of WAAS. Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters. The U.S. Coast Guard operates the most common DGPS correction service. This system consists of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters. In order to get the corrected signal, users must have a differential beacon receiver and beacon antenna in addition to their GPS.

The GPS satellite system

The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour.

GPS satellites are powered by solar energy. They have backup batteries onboard to keep them running in the event of a solar eclipse, when there's no solar power. Small rocket boosters on each satellite keep them flying in the correct path.

Here are some other interesting facts about the GPS satellites (also called NAVSTAR, the official U.S. Department of Defense name for GPS):

  • The first GPS satellite was launched in 1978.
  • A full constellation of 24 satellites was achieved in 1994.
  • Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
  • A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
  • Transmitter power is only 50 watts or less.

What's the signal?

GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.

A GPS signal contains three different bits of information - a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your Garmin GPS unit's satellite page, as it identifies which satellites it's receiving.

Ephemeris data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.

The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.

Sources of GPS signal errors

Factors that can degrade the GPS signal and thus affect accuracy include the following:

  • Ionosphere and troposphere delays - The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
  • Signal multipath - This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
  • Receiver clock errors - A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors.
  • Orbital errors - Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
  • Number of satellites visible - The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
  • Satellite geometry/shading - This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
  • Intentional degradation of the satellite signal - Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.

www.satelite.com

Gps block i - Wikipedia

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en.m.wikipedia.org

satellite gps - Русский перевод – Словарь Linguee

This is combined with coordinate data from global positioning satellites (GPS).

daccess-ods.un.org

Она сопрягается с координатными данными от геопозиционных спутников (ГПС).

daccess-ods.un.org

The new HDD series is an ideal proposition to telematics manufacturers improving the in-vehicle user experience by integrating

[...]

automotive

[...] infotainment systems, self-diagnostic systems, satellite GPS, navigation and communication tools [...]

into premium automobiles.

storage.toshiba.eu

Жесткие диски новой серии идеально подходят для производителей средств обработки и передачи информации, позволяя расширить возможности пользователей и интегрировать в

[...]

автомобили премиум-класса

[...] информационно-развлекател ь ные и диагностические системы, а также инструменты спутниковой [...]

GPS-навигации и общения.

storage.toshiba.eu

In many of advanced countries topographic industry is being developed and improved,

[...]

specialists use the most modern

[...] technologies including satellite (GPS) geodesic receivers, allowing [...]

performing required work volume promptly and properly.

gosreg.kg

Во многих развитых странах топографическая индустрия развивается и усовершенствуется,

[...]

специалисты применяют самые

[...] современные технологии, в том числе и спутниковые (GPS) геодезические [...]

приёмники, позволяющие

[...]

выполнить необходимый объём работ качественно и быстро.

gosreg.kg

IDGMI’s mission is to invest in companies with

[...]

development in the following

[...] industries: communication, media, satellite, GPS, biometric data capture and [...]

monitoring as well as in

[...]

consumer products and related accessories.

galaxier.com

Миссия IDGMI в том, чтобы инвестировать в

[...]

компании с развитием в

[...] следующих отраслях промышленности: связь, средства массовой информации, спутник, [...]

GPS, биометрического сбора

[...]

данных и мониторинга, а также в потребительских товарах и аксессуары к ним.

galaxier.com

Besides seeing the American satellite GPS signals it also already [...]

receives the Russian GLONASS satellite signals and thus

[...]

is ready for the European GALILEO system.

info.amazone.de

С этим прибором будущего

[...]

поколения клиент будет отлично

[...] подготовлен: наряду с сигналами американской GPS, он принимает [...]

сигналы российской GLONASS,

[...]

а также европейской системы GALILEO.

info.amazone.de

Pirates often

[...] now have Global Positioning Satellite (GPS) equipment and heavier weapons, [...]

including rocket-propelled grenades.

daccess-ods.un.org

Теперь пираты часто имеют аппаратуру

[...] Глобальной системы определения координат (ГСОК), крупнокалиберное оружие, [...]

в том числе реактивные гранаты.

daccess-ods.un.org

Sophistication of the modus operandi (increasing use of “mother

[...]

ships” to backstop

[...] attack skiffs, global positioning satellites (GPS), Automatic Identification System [...]

(AIS) data, satellite

[...]

telephones and counterfeit detectors; organization of refuelling at sea of captured ships for the trip to Somalia).

daccess-ods.un.org

более изощренный способ действий (расширение использования судовбаз для тыловой поддержки абордажных лодок, глобальной системы

[...]

определения координат (ГСОК),

[...] данных автоматической системы опознавания, спутниковых телефонов и детекторов купюр; [...]

организация дозаправки

[...]

в море захваченных судов для движения в Сомали).

daccess-ods.un.org

The applied satellite GPS-GSM technology provides for maximum system [...]

flexibility at managing the future increase in cargo

[...]

transport volume and roads network extension in the Slovak Republic.

emyto.sk

Используемая технология GPS – GSM обеспечивает максимальную гибкость [...]

системы, чтобы можно было справиться с возрастанием

[...]

объема грузоперевозок и расширением сети автодорог в Словацкой Республике.

emyto.sk

Dr. John Gould, the Director of the International Project Offices for CLIVAR and WOCE provided a

[...]

retrospective on WOCE and the

[...] development of new break-through technologies (satellite altimetry, GPS, profiling floats) that made possible the new discoveries [...]

about the dynamics

[...]

of the ocean and set the stage for CLIVAR.

unesdoc.unesco.org

Д-р Джон Гоулд, директор международных проектных

[...]

бюро КЛИВАР и ВОСЕ,

[...] рассказал об истории ВОСЕ и развитии новых передовых технологий (спутниковая альтиметрия, глобальная система определения местоположения, [...]

буи-профилографы),

[...]

которые позволяют делать новые открытия в отношении динамики океана и готовят поле деятельности для КЛИВАР.

unesdoc.unesco.org

The name and frequency of the selected radio station will appear at the

[...]

top of this window, together with signal

[...] strength information indicated by a bar similar to the GPS satellite signal strength bars on the GPS Data screen.

marketing.prestigio.com

В верхней части этого экрана отображаются название и частота

[...]

выбранной радиостанции, а также информация о

[...] силе сигнала в виде строки, подобной той, которой обозначается сила сигнала спутника GPS на экране GPS-данные.

marketing.prestigio.com

These systems use the GPS satellite network to track your car on a [...]

computer screen.

macbook-covers.net

Эти системы используют сеть спутниковой GPS для отслеживания вашего автомобиля [...]

на экране компьютера.

macbook-covers.net

The Kazakdarya agronomist Mr. Genjemurat

[...]

Turymbetov received good training on

[...] the use of the satellite-based maps and GPS from Mr. Peter [...]

Navratil, GTZ expert and he is

[...]

proficient in the use of these spatial technologies.

fao.org

Агроном Казакдарьинского участка Г-н

[...]

Генжемурат Турымбетов получил

[...] хорошее обучение работе со спутниковыми картами от Г-на Петера [...]

Навратила, эксперта ГТЦ, и он без

[...]

труда пользуется такими технологиями.

fao.org

Nicaragua’s primary interest has been and continues to be to benefit from access to satellite technology for use in aviation communications, meteorology and geographical information systems such as the global positioning system (GPS).

daccess-ods.un.org

Основной интерес Никарагуа был и продолжает оставаться в получении преимуществ от доступа к спутниковой технологии для использования в авиационной связи, метеорологии и в системах географической информации, таких как глобальная навигационная система (GPS).

daccess-ods.un.org

A world without cell phones, computer systems, GPS navigation, etc, is hardly conceivable nowadays. Violent solar storms are a serious threat to contemporary lifestyle as they can cause major failures onboard spacecraft, aircrafts, satellite communication, electric power grids and all electronic devices that we use every day.

istc.ru

В настоящее время мир практически немыслим без мобильных телефонов, компьютеров, глобальных навигационных спутниковых систем и т.д. Сильные солнечные бури представляют серьезную угрозу для современного ообщества, поскольку они могут вызвать сбои аппаратуры, установленной на борту космических аппаратов и самолетов, спутниковой связи, линий электропередачи и, вообще, всех электронных устройств, которыми мы пользуемся каждый день.

istc.ru

Since the introduction of GPS satellite technology in the agricultural industry, ever greater numbers of [...]

businesses in the sector have turned to the benefits of this system.

claas.co.uk

Обороты двигателя,

[...]

скорость движения

[...] (система контроля скорости) С момента проникновения спутниковой техники GPS в сельское хозяйство все больше [...]

предприятий используют

[...]

ее преимущества.

claas.com

With its vast land areas and territorial waters,

[...] low population density and sub-Arctic to Arctic location, Norway benefits immensely from the GPS satellite navigation system.

oosa.unvienna.org

Для Норвегии с ее протяженными

[...]

участками суши и территориальными водами, низкой

[...] плотностью населения, субарктическим и арктическим климатом применение спутниковой навигационной системы GPS имеет колоссальное [...]

значение.

oosa.unvienna.org

The implementation of the project will allow SITRONICS to manufacture products designed for

[...]

the emerging mass

[...] markets, such as digital television, GLONASS/ GPS satellite positioning, industrial electronic components, [...]

versatile high-security

[...]

smart-cards (biometric passports and other personal documents, bank and social security cards, SIM-cards) and RFID-tags.

sitronics.com

Благодаря реализации проекта СИТРОНИКС будет выпускать продукты, нацеленные на

[...]

развивающиеся массовые рынки,

[...] такие как цифровое телевидение, спутниковая навигация ГЛОНАСС/GPS, компоненты для промышленной электроники, [...]

смарт-карты

[...]

с расширенной функциональностью и высокой степенью защиты (биометрические паспорта и другие персональные документы, банковские и социальные карты, SIM-карты) и RFID-метки.

sitronics.ru

This is because some video transmitters radiate

[...] radio frequency energy that is on the same frequency as GPS satellite signals.

eagletreesystems.com

Это потому, что некоторые из

[...] видеопередатчиков работают на той же частоте, что GPS принимает сигналы спутников.

eagletreesystems.com

All the car-transporters are provided with GPS satellite tracking systems, which allow to give operative and exact [...]

information about existing location of

[...]

a load for a client; also the customer can personally observe the route of our transporting load online.

manvesta.lt

Все автовозы обеспечены спутниковыми системами наблюдения (GPS), которые позволяют предоставить клиенту оперативную [...]

и точную информацию о месте нахождения

[...]

груза, также клиент сам может наблюдать за путем перевозимого груза в реальном времени.

manvesta.lt

The space-based segment comprises five satellites aboard which, inter alia, the following equipment is to be installed: radiophysical systems that use a wide range of frequencies (ionosondes) for monitoring the state of the ionosphere; equipment for the measurement of ionizing radiation; a system to monitor magnetic and wave activity; a dual-frequency transmitter of radio signals at frequencies of 150 to 400 MHz; global positioning system (GPS) receivers; and a diagnostics system to monitor solar activity.

daccess-ods.un.org

Космический сегмент включает в свой состав пять КА, на борту которых предусмотрена установка такой аппаратуры, как: широкополосные радиофизические комплексы (ионозонды) для контроля состояния планетарной ионосферы, аппаратура диагностики ионизирующих излучений, комплекс магнитной и волновой активности, двухчастотный передатчик радиосигналов на частотах 150/400 МГц, приемники GPS и диагностический комплекс солнечной активности.

daccess-ods.un.org

With the aid of GPS satellite signals and other positioning sensors, the OBU automatically determines how many kilometres have already been driven [...]

on the toll route,

[...]

calculates the toll based on the vehicle and toll rate information that has been entered and transmits this information to the Toll Collect computer centre for further processing.

lontex.pl

При помощи сателлитных сигналов GPS и при поддержке сенсоров определения местонахождения, автоматически распознает проходимые этапы маршрута. [...]

OBU автоматично вычисляет

[...]

дорожный сбор и передает полученные данные через мобильную связь в вычислительный центр Toll Collect.

lontex.pl

The template contained three segments which were: (1) Details of the location of the

[...]

delivery system allowing for

[...] both Geo Positioning System (GPS) and map references data; (2) [...]

Characteristics of the intended

[...]

target as seen from the firing point and the type of explosive ordnance used; and (3) Details of the mean point of impact of the ordnance, the number of rounds delivered and if relevant, the predicted dispersion of the ordnance.

daccess-ods.un.org

Шаблон содержит три сегмента, а именно: 1) сведения о местоположении системы

[...]

доставки в сочетании с

[...] возможностью использовать как данные глобальной системы местоопределения [...]

(GPS), так и картографические координатные

[...]

данные; 2) характеристики намечаемой цели, как это видится с огневого рубежа, и тип применяемых взрывоопасных боеприпасов; и 3) сведения о средней точке попадания боеприпасов, количестве доставленных выстрелов и, если уместно, прогнозируемом разбросе снарядов.

daccess-ods.un.org

GPS data are useful for quick determination of the earthquake [...]

characteristics and should be part of the tsunami warning system.

unesdoc.unesco.org

Данные

[...] Глобальной системы местоопределения (GPS) полезны для быстрого [...]

определения характеристик землетрясения и должны быть

[...]

частью системы предупреждения о цунами.

unesdoc.unesco.org

The Internet and mobile telecommunication systems

[...] are integral to GIS, such as GPS and remote sensing.

daccess-ods.un.org

Интернет и системы мобильной связи составляют

[...] неотъемлемую часть ГИС, например ГПС и дистанционного [...]

зондирования.

daccess-ods.un.org

The General Organization of Remote Sensing (GORS) made use of space data in the implementation of many development studies and projects, in addition to internal and external training

[...]

courses in the various techniques and

[...] applications of remote sensing, as well as other subsystems, such as GIS and GPS.

oosa.unvienna.org

Генеральная организация по дистанционному зондированию (ГОДЗ) использует космические данные в осуществлении многочисленных исследований и проектов в области развития и, кроме того, во внутренних и внешних учебных курсах по различным методам и видам применения дистанционного

[...]

зондирования, а также других

[...] подсистем, таких как Географическая информационная система (ГИС) и Глобальная система [...]

определения местонахождения (GPS).

oosa.unvienna.org

All OST providers (specialist services and GPs) should be trained in HIV and hepatitis-related issues [...]

and be able to provide education about blood-borne

[...]

virus issues for clients/tangata whai ora; their significant others, family and wha¯ nau; and other health and social service providers as part of their specialist consultation and liaison role.

uiphp.org.ua

Все предоставители

[...] ОЗТ (представители службы по оказанию специальных услуг и врачи общей практики) должны быть обучены по [...]

вопросам ВИЧ-инфекции и

[...]

гепатитов и должны быть способны проконсультировать клиента, членов его семьи и близких относительно передающихся через кровь вирусов, а также предоставить всю необходимую информацию предоставителям других социальных и медицинских услуг как часть своих консультативных и посреднических обязанностей.

uiphp.org.ua

A number of national projects were carried out covering a wide range of topics such as

[...]

management of tropical forests; water resources;

[...] vulnerable ecosystems; development of university curricula for postgraduate diplomas in geographic information systems and satellite applications; ground water and mountain aquifer management; and satellite data processing and analysis.

unesdoc.unesco.org

Был осуществлен ряд национальных проектов, охватывающих широкий круг вопросов, как, например, управление тропическими лесами; водные ресурсы; уязвимые экосистемы; разработка

[...]

университетских учебных программ для получения

[...] диплома о послеуниверситетском образовании в области применения системы географической информации и спутников; управление подземными водами и водоносными слоями горных районов, а также обработка и анализ данных, получаемых со спутников.

unesdoc.unesco.org

Finally, national websites were developed to promote and disseminate the results of national projects; the global website is being

[...]

transformed into the first UNESCO –

[...] African Portal in Remote Sensing and Satellite Applications for Sustainable Development.

unesdoc.unesco.org

Наконец, были созданы национальные вебсайты для популяризации и распространения результатов национальных проектов; глобальный веб-сайт

[...]

преобразуется в первый портал

[...] ЮНЕСКО-Африки по использованию дистанционного зондирования и спутников в целях [...]

устойчивого развития.

unesdoc.unesco.org

Building on these national achievements, the Republic of Korea expanded its cooperation with the international space community by establishing new partnerships with countries such as India, Italy, Kazakhstan and the Netherlands, and strengthening existing partnerships in various areas of

[...]

aerospace research and development,

[...] including joint research on satellite technology and its applications, [...]

Earth science and space exploration.

oosa.unvienna.org

Опираясь на эти национальные достижения, Республика Корея углубила сотрудничество с международным космическим сообществом, установив новые партнерские отношения с такими странами, как Индия, Италия, Казахстан и Нидерланды, и укрепив ранее установленные

[...]

отношения в различных областях

[...] аэрокосмических исследований и развития, в том числе в сфере совместного [...]

исследования спутниковых

[...]

технологий и их применения, землеведения и освоения космоса.

oosa.unvienna.org

Turning to question 15, he said that efforts towards the educational integration of children from marginalized communities included the establishment of satellite schools; local language teaching during the first three years, with English as a subject of study; and the introduction of mobile schools for the nomadic Ovahimba people.

daccess-ods.un.org

Касаясь вопроса 15, он говорит, что меры по интеграции детей из маргинализованных общин в систему образования включают создание школспутников; преподавание местного языка в течение первых трех лет обучения с английским языком в качестве учебного предмета; а также организацию передвижных школ для общины овахимба, ведущей кочевой образ жизни.

daccess-ods.un.org

www.linguee.ru

Satellite navigation - Wikipedia

A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows small electronic receivers to determine their location (longitude, latitude, and altitude/elevation) to high precision (within a few metres) using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking). The signals also allow the electronic receiver to calculate the current local time to high precision, which allows time synchronisation. Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.

A satellite navigation system with global coverage may be termed a global navigation satellite system (GNSS). As of December 2016[update], only the United States' Global Positioning System (GPS), Russia's GLONASS and the European Union's Galileo are global operational GNSSs. The European Union's Galileo GNSS is scheduled to be fully operational by 2020.[1]China is in the process of expanding its regional BeiDou Navigation Satellite System into the global BeiDou-2 GNSS by 2020.[2]India, France and Japan are in the process of developing regional navigation and augmentation systems as well.

Global coverage for each system is generally achieved by a satellite constellation of 18–30 medium Earth orbit (MEO) satellites spread between several orbital planes. The actual systems vary, but use orbital inclinations of >50° and orbital periods of roughly twelve hours (at an altitude of about 20,000 kilometres or 12,000 miles).

Classification[edit]

Satellite navigation systems that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:[3]

  • GNSS-1[citation needed] is the first generation system and is the combination of existing satellite navigation systems (GPS and GLONASS), with Satellite Based Augmentation Systems (SBAS) or Ground Based Augmentation Systems (GBAS). In the United States, the satellite based component is the Wide Area Augmentation System (WAAS), in Europe it is the European Geostationary Navigation Overlay Service (EGNOS), and in Japan it is the Multi-Functional Satellite Augmentation System (MSAS). Ground based augmentation is provided by systems like the Local Area Augmentation System (LAAS).[citation needed]
  • GNSS-2[citation needed] is the second generation of systems that independently provides a full civilian satellite navigation system, exemplified by the European Galileo positioning system. These systems will provide the accuracy and integrity monitoring necessary for civil navigation; including aircraft. This system consists of L1 and L2 frequencies (in the L band of the radio spectrum) for civil use and L5 for system integrity. Development is also in progress to provide GPS with civil use L2 and L5 frequencies[4], making it a GNSS-2 system.¹[citation needed]
  • Core Satellite navigation systems, currently GPS (United States), GLONASS (Russian Federation), Galileo (European Union) and Compass (China).
  • Global Satellite Based Augmentation Systems (SBAS) such as Omnistar and StarFire.
  • Regional SBAS including WAAS (US), EGNOS (EU), MSAS (Japan) and GAGAN (India).
  • Regional Satellite Navigation Systems such as China's Beidou, India's NAVIC, and Japan's proposed QZSS.
  • Continental scale Ground Based Augmentation Systems (GBAS) for example the Australian GRAS and the joint US Coast Guard, Canadian Coast Guard, US Army Corps of Engineers and US Department of Transportation National Differential GPS (DGPS) service.
  • Regional scale GBAS such as CORS networks.
  • Local GBAS typified by a single GPS reference station operating Real Time Kinematic (RTK) corrections.

History and theory[edit]

Ground based radio navigation has long been practiced. The DECCA, LORAN, GEE and Omega systems used terrestrial longwave radio transmitters which broadcast a radio pulse from a known "master" location, followed by a pulse repeated from a number of "slave" stations. The delay between the reception of the master signal and the slave signals allowed the receiver to deduce the distance to each of the slaves, providing a fix.

The first satellite navigation system was Transit, a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect: the satellites travelled on well-known paths and broadcast their signals on a well-known radio frequency. The received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position.

Part of an orbiting satellite's broadcast included its precise orbital data. In order to ensure accuracy, the US Naval Observatory (USNO) continuously observed the precise orbits of these satellites. As a satellite's orbit deviated, the USNO would send the updated information to the satellite. Subsequent broadcasts from an updated satellite would contain its most recent ephemeris.

Modern systems are more direct. The satellite broadcasts a signal that contains orbital data (from which the position of the satellite can be calculated) and the precise time the signal was transmitted. The orbital ephemeris is transmitted in a data message that is superimposed on a code that serves as a timing reference. The satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation. The receiver compares the time of broadcast encoded in the transmission of three (at sea level) or four different satellites, thereby measuring the time-of-flight to each satellite. Several such measurements can be made at the same time to different satellites, allowing a continual fix to be generated in real time using an adapted version of trilateration: see GNSS positioning calculation for details.

Each distance measurement, regardless of the system being used, places the receiver on a spherical shell at the measured distance from the broadcaster. By taking several such measurements and then looking for a point where they meet, a fix is generated. However, in the case of fast-moving receivers, the position of the signal moves as signals are received from several satellites. In addition, the radio signals slow slightly as they pass through the ionosphere, and this slowing varies with the receiver's angle to the satellite, because that changes the distance through the ionosphere. The basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centred on four satellites. Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.

Civil and military uses[edit]

Satellite navigation using a laptop and a GPS receiver

The original motivation for satellite navigation was for military applications. Satellite navigation allows precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from mis-directed weapons. (See Guided bomb). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war.

The ability to supply satellite navigation signals is also the ability to deny their availability. The operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires.

Global navigation satellite systems[edit]

launched GNSS satellites 1978 to 2014

GPS[edit]

The United States' Global Positioning System (GPS) consists of up to 32 medium Earth orbit satellites in six different orbital planes, with the exact number of satellites varying as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is currently the world's most utilized satellite navigation system.

GLONASS[edit]

The formerly Soviet, and now Russian, Global'naya Navigatsionnaya Sputnikovaya Sistema (Russian: ГЛОбальная НАвигационная Спутниковая Система, GLObal NAvigation Satellite System), or GLONASS, is a space-based satellite navigation system that provides a civilian radionavigation-satellite service and is also used by the Russian Aerospace Defence Forces. The full orbital constellation of 24 GLONASS satellites enables full global coverage.

Galileo[edit]

The European Union and European Space Agency agreed in March 2002 to introduce their own alternative to GPS, called the Galileo positioning system. Galileo became operational on 15 December 2016 (global Early Operational Capability (EOC)) [5] At an estimated cost of €3 billion,[6] the system of 30 MEO satellites was originally scheduled to be operational in 2010. The original year to become operational was 2014.[7] The first experimental satellite was launched on 28 December 2005.[8] Galileo is expected to be compatible with the modernized GPS system. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy. Galileo is expected to be in full service in 2020 and at a substantially higher cost.[1] The main modulation used in Galileo Open Service signal is the Composite Binary Offset Carrier (CBOC) modulation.

BeiDou-2[edit]

China has indicated they plan to complete the entire second generation Beidou Navigation Satellite System (BDS or BeiDou-2, formerly known as COMPASS), by expanding current regional (Asia-Pacific) service into global coverage by 2020.[2] The BeiDou-2 system is proposed to consist of 30 MEO satellites and five geostationary satellites. A 16-satellite regional version (covering Asia and Pacific area) was completed by December 2012.

Regional navigation satellite systems[edit]

BeiDou-1[edit]

Chinese regional (Asia-Pacific, 16 satellites) network to be expanded into the whole BeiDou-2 global system which consists of all 35 satellites by 2020.

NAVIC[edit]

The NAVIC or NAVigation with Indian Constellation is an autonomous regional satellite navigation system developed by Indian Space Research Organisation (ISRO) which would be under the total control of Indian government. The government approved the project in May 2006, with the intention of the system completed and implemented on 28 April 2016. It will consist of a constellation of 7 navigational satellites.[9] 3 of the satellites will be placed in the Geostationary orbit (GEO) and the remaining 4 in the Geosynchronous orbit(GSO) to have a larger signal footprint and lower number of satellites to map the region. It is intended to provide an all-weather absolute position accuracy of better than 7.6 meters throughout India and within a region extending approximately 1,500 km around it.[10] A goal of complete Indian control has been stated, with the space segment, ground segment and user receivers all being built in India.[11] All seven satellites, IRNSS-1A, IRNSS-1B, IRNSS-1C, IRNSS-1D, IRNSS-1E, IRNSS-1F, and IRNSS-1G, of the proposed constellation were precisely launched on 1 July 2013, 4 April 2014, 16 October 2014, 28 March 2015, 20 January 2016, 10 March 2016 and 28 April 2016 respectively from Satish Dhawan Space Centre.[12][13] The system is expected to be fully operational by August 2016.[14]

QZSS[edit]

The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and enhancement for GPS covering Japan. The first demonstration satellite was launched in September 2010.[15]

Comparison of systems[edit]

System BeiDou Galileo GLONASS GPS NAVIC QZSS Owner Coverage Coding Orbital altitude Period Revolutions per sidereal day Number ofsatellites Frequency Status Precision System BeiDou Galileo GLONASS GPS NAVIC QZSS
China EU Russia United States India Japan
Regional(Global by 2020) Global Global Global Regional Regional
CDMA CDMA FDMA CDMA CDMA CDMA
21,150 km (13,140 mi) 23,222 km (14,429 mi) 19,130 km (11,890 mi) 20,180 km (12,540 mi) 36,000 km (22,000 mi) 32,000 km (20,000 mi)
12.63 h (12 h 38 min) 14.08 h (14 h 5 min) 11.26 h (11 h 16 min) 11.97 h (11 h 58 min) 1436.0m (IRNSS-1A)1436.1m (IRNSS-1B)1436.1m (IRNSS-1C)1436.1m (IRNSS-1D)1436.1m (IRNSS-1E)1436.0m (IRNSS-1F)1436.1m (IRNSS-1G)  
17/9 17/10 17/8 2    
5 geostationary orbit (GEO) satellites,30 medium Earth orbit (MEO) satellites 24 by design,14 operational,4 commissioning,30 operational satellites budgeted 28 (at least 24 by design) including:[16]24 operational2 under check by the satellite prime contractor2 in flight tests phase 31 (at least 24 by design)[17] 3 geostationary orbit (GEO) satellites,5 geosynchronous (GSO) medium Earth orbit (MEO) satellites In 2011 the Government of Japan has decided to accelerate the QZSS deployment in order to reach a 4-satellite constellation by the late 2010s, while aiming at a final 7-satellite constellation in the future
1.561098 GHz (B1)1.589742 GHz (B1-2)1.20714 GHz (B2)1.26852 GHz (B3) 1.164–1.215 GHz (E5a and E5b)1.260–1.300 GHz (E6)1.559–1.592 GHz (E2-L1-E11) Around 1.602 GHz (SP)Around 1.246 GHz (SP) 1.57542 GHz (L1 signal)1.2276 GHz (L2 signal) 1176.45 MHz(L5 Band)2492.028 MHz (S Band)  
22 satellites operational,40 additional satellites 2016-2020 18 satellites operational12 additional satellites 2017-2020 Operational Operational 6 satellites fully operational,IRNSS-1A partially operational  
10m (Public)0.1m (Encrypted) 1m (Public)0.01m (Encrypted) 4.5m – 7.4m 15m (Without DGPS or WAAS) 10m (Public)0.1m (Encrypted) 1m (Public)0.1m (Encrypted)

Augmentation[edit]

GNSS augmentation is a method of improving a navigation system's attributes, such as accuracy, reliability, and availability, through the integration of external information into the calculation process, for example, the Wide Area Augmentation System, the European Geostationary Navigation Overlay Service, the Multi-functional Satellite Augmentation System, Differential GPS, GPS Aided GEO Augmented Navigation (GAGAN) and inertial navigation systems.

DORIS[edit]

Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a French precision navigation system. Unlike other GNSS systems, it is based on static emitting stations around the world, the receivers being on satellites, in order to precisely determine their orbital position. The system may be used also for mobile receivers on land with more limited usage and coverage. Used with traditional GNSS systems, it pushes the accuracy of positions to centimetric precision (and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of Earth rotation and deformations), in order to build a much more precise geodesic reference system.[18]

Low Earth orbit satellite phone networks[edit]

The two current operational low Earth orbit satellite phone networks are able to track transceiver units with accuracy of a few kilometers using doppler shift calculations from the satellite. The coordinates are sent back to the transceiver unit where they can be read using AT commands or a graphical user interface.[19][20] This can also be used by the gateway to enforce restrictions on geographically bound calling plans.

Positioning calculation[edit]

See also[edit]

  1. ^ Orbital periods and speeds are calculated using the relations 4π²R³ = T²GM and V²R = GM, where R = radius of orbit in metres, T = orbital period in seconds, V = orbital speed in m/s, G = gravitational constant ≈ 6.673×10−11 Nm²/kg², M = mass of Earth ≈ 5.98×1024 kg.
  2. ^ Approximately 8.6 times (in radius and length) when the moon is nearest (363 104 km ÷ 42 164 km) to 9.6 times when the moon is farthest (405 696 km ÷ 42 164 km).

References[edit]

Further reading[edit]

  • Office for Outer Space Affairs of the United Nations (2010), Report on Current and Planned Global and Regional Navigation Satellite Systems and Satellite-based Augmentation Systems. [2]

External links[edit]

Information on specific GNSS systems[edit]

Organizations related to GNSS[edit]

Supportive or illustrative sites[edit]

en.wikipedia.org

GPS Satellite navigation

 

The GPS User Segment consists of the GPS receivers and the user community. GPS receivers convert SV signals into position, velocity, and time estimates. Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time. GPS receivers are used for navigation, positioning, time dissemination, and other research.

  • Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals.
  • Precise positioning is possible using GPS receivers at reference locations providing corrections and relative positioning data for remote receivers. Surveying, geodetic control, and plate tectonic studies are examples.
  • Time and frequency dissemination, based on the precise clocks on board the SVs and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
  • Research projects have used GPS signals to measure atmospheric parameters.
Precise Positioning Service(PPS)
  • Authorized users with cryptographic equipment and keys and specially equipped receivers use the Precise Positioning System. U.S. and Allied military, certain U.S. Government agencies, and selected civil users specifically approved by the U.S. Government, can use the PPS.
  • PPS Predictable Accuracy
    • 22 meter Horizontal accuracy
    • 27.7 meter vertical accuracy
    • 100 nanosecond time accuracy
Standard Positioning Service(SPS)
  • Civil users worldwide use the SPS without charge or restrictions. Most receivers are capable of receiving and using the SPS signal. The SPS accuracy is intentionally degraded by the DOD by the use of Selective Availability.
  • SPS Predictable Accuracy
    • 100 meter horizontal accuracy
    • 156 meter vertical accuracy
    • 340 nanoseconds time accuracy
  • These GPS accuracy figures are from the 1994 Federal Radionavigation Plan. The figures are 95% accuracies, and express the value of two standard deviations of radial error from the actual antenna position to an ensemble of position estimates made under specified satellite elevation angle (five degrees) and PDOP (less than six) conditions.
  • For horizontal accuracy figures 95% is the equivalent of 2drms (two-distance root-mean-squared), or twice the radial error standard deviation. For vertical and time errors 95% is the value of two-standard deviations of vertical error or time error.
  • Receiver manufacturers may use other accuracy measures. Root-mean-square (RMS) error is the value of one standard deviation (68%) of the error in one, two or three dimensions. Circular Error Probable (CEP) is the value of the radius of a circle, centered at the actual position that contains 50% of the position estimates. Spherical Error Probable (SEP) is the spherical equivalent of CEP, that is the radius of a sphere, centered at the actual position, that contains 50% of the three dimension position estimates. As opposed to 2drms, drms, or RMS figures, CEP and SEP are not affected by large blunder errors making them an overly optimistic accuracy measure
  • Some receiver specification sheets list horizontal accuracy in RMS or CEP and without Selective Availability, making those receivers appear more accurate than those specified by more responsible vendors using more conservative error measures.
  • The GPS Navigation Message consists of time-tagged data bits marking the time of transmission of each subframe at the time they are transmitted by the SV. A data bit frame consists of 1500 bits divided into five 300-bit subframes. A data frame is transmitted every thirty seconds. Three six-second subframes contain orbital and clock data. SV Clock corrections are sent in subframe one and precise SV orbital data sets (ephemeris data parameters) for the transmitting SV are sent in subframes two and three. Subframes four and five are used to transmit different pages of system data. An entire set of twenty-five frames (125 subframes) makes up the complete Navigation Message that is sent over a 12.5 minute period.
  • Data frames (1500 bits) are sent every thirty seconds. Each frame consists of five subframes.
  • Data bit subframes (300 bits transmitted over six seconds) contain parity bits that allow for data checking and limited error correction.
  • Clock data parameters describe the SV clock and its relationship to GPS time.
  • Ephemeris data parameters describe SV orbits for short sections of the satellite orbits. Normally, a receiver gathers new ephemeris data each hour, but can use old data for up to four hours without much error. The ephemeris parameters are used with an algorithm that computes the SV position for any time within the period of the orbit described by the ephemeris parameter set.
  • Almanacs are approximate orbital data parameters for all SVs. The ten-parameter almanacs describe SV orbits over extended periods of time (useful for months in some cases) and a set for all SVs is sent by each SV over a period of 12.5 minutes (at least). Signal acquisition time on receiver start-up can be significantly aided by the availability of current almanacs. The approximate orbital data is used to preset the receiver with the approximate position and carrier Doppler frequency (the frequency shift caused by the rate of change in range to the moving SV) of each SV in the constellation.
  • Each complete SV data set includes an ionospheric model that is used in the receiver to approximates the phase delay through the ionosphere at any location and time.
  • Each SV sends the amount to which GPS Time is offset from Universal Coordinated Time. This correction can be used by the receiver to set UTC to within 100 ns
  • Other system parameters and flags are sent that characterize details of the system.
Code Phase Tracking (Navigation)
  • The GPS receiver produces replicas of the C/A and/or P (Y)-Code. Each PRN code is a noise-like, but pre-determined, unique series of bits.
  • The receiver produces the C/A code sequence for a specific SV with some form of a C/A code generator. Modern receivers usually store a complete set of precomputed C/A code chips in memory, but a hardware, shift register, implementation can also be used.
  • The C/A code generator produces a different 1023 chip sequence for each phase tap setting. In a shift register implementation the code chips are shifted in time by slewing the clock that controls the shift registers. In a memory lookup scheme the required code chips are retrieved from memory.

see also C/A Code Phase Assignments

  • The C/A code generator repeats the same 1023-chip PRN-code sequence every millisecond. PRN codes are defined for 32 satellite identification numbers.
  • The receiver slides a replica of the code in time until there is correlation with the SV code.
  • If the receiver applies a different PRN code to an SV signal there is no correlation.
  • When the receiver uses the same code as the SV and the codes begin to line up, some signal power is detected.
  • As the SV and receiver codes line up completely, the spread-spectrum carrier signal is de-spread and full signal power is detected.
  • A GPS receiver uses the detected signal power in the correlated signal to align the C/A code in the receiver with the code in the SV signal. Usually a late version of the code is compared with an early version to insure that the correlation peak is tracked.
  • A phase locked loop that can lock to either a positive or negative half-cycle (a bi-phase lock loop) is used to demodulate the 50 HZ navigation message from the GPS carrier signal. The same loop can be used to measure and track the carrier frequency (Doppler shift) and by keeping track of the changes to the numerically controlled oscillator, carrier frequency phase can be tracked and measured.
  • The receiver PRN code start position at the time of full correlation is the time of arrival (TOA) of the SV PRN at receiver. This TOA is a measure of the range to SV offset by the amount to which the receiver clock is offset from GPS time. This TOA is called the pseudo-range.
Pseudo-Range Navigation
  • The position of the receiver is where the pseudo-ranges from a set of SVs intersect.
  • Position is determined from multiple pseudo-range measurements at a single measurement epoch. The pseudo range measurements are used together with SV position estimates based on the precise orbital elements (the ephemeris data) sent by each SV. This orbital data allows the receiver to compute the SV positions in three dimensions at the instant that they sent their respective signals.
  • Four satellites (normal navigation) can be used to determine three position dimensions and time. Position dimensions are computed by the receiver in Earth-Centered, Earth-Fixed X, Y, Z (ECEF XYZ) coordinates.
  • Time is used to correct the offset in the receiver clock, allowing the use of an inexpensive receiver clock.
  • SV Position in XYZ is computed from four SV pseudo-ranges and the clock correction and ephemeris data.
  • Receiver position is computed from the SV positions, the measured pseudo-ranges (corrected for SV clock offsets, ionospheric delays, and relativistic effects), and a receiver position estimate (usually the last computed receiver position).
  • Three satellites could be used determine three position dimensions with a perfect receiver clock. In practice this is rarely possible and three SVs are used to compute a two-dimensional, horizontal fix (in latitude and longitude) given an assumed height. This is often possible at sea or in altimeter equipped aircraft.
  • Five or more satellites can provide position, time and redundancy. More SVs can provide extra position fix certainty and can allow detection of out-of-tolerance signals under certain circumstances.
Receiver Position, Velocity, and Time
  • Position in XYZ is converted within the receiver to geodetic latitude, longitude and height above the ellipsoid.
  • Latitude and longitude are usually provided in the geodetic datum on which GPS is based (WGS-84). Receivers can often be set to convert to other user-required datums. Position offsets of hundreds of meters can result from using the wrong datum.
  • Velocity is computed from change in position over time, the SV Doppler frequencies, or both.
  • Time is computed in SV Time, GPS Time, and UTC.
  • SV Time is the time maintained by each satellite. Each SV contains four atomic clocks (two cesium and two rubidium). SV clocks are monitored by ground control stations and occasionally reset to maintain time to within one-millisecond of GPS time. Clock correction data bits reflect the offset of each SV from GPS time.
  • SV Time is set in the receiver from the GPS signals. Data bit subframes occur every six seconds and contain bits that resolve the Time of Week to within six seconds. The 50 Hz data bit stream is aligned with the C/A code transitions so that the arrival time of a data bit edge (on a 20 millisecond interval) resolves the pseudo-range to the nearest millisecond. Approximate range to the SV resolves the twenty millisecond ambiguity, and the C/A code measurement represents time to fractional milliseconds. Multiple SVs and a navigation solution (or a known position for a timing receiver) permit SV Time to be set to an accuracy limited by the position error and the pseudo-range error for each SV.

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