Sabtu, 29 Mei 2010

Globa Positioning System

Global Positioning System
Global Positioning System (GPS), space-based radio-navigation system (see Navigation), consisting of 24 satellites and ground support. GPS provides users with accurate information about their position and velocity, as well as the time, anywhere in the world and in all weather conditions.
GPS, formally known as the Navstar Global Positioning System, was initiated in 1973 to reduce the proliferation of navigation aids. GPS is operated and maintained by the United States Department of Defense. By creating a system that overcame the limitations of many existing navigation systems, GPS became attractive to a broad spectrum of users. GPS has been successful in classical navigation applications, and because its capabilities are accessible using small, inexpensive equipment, GPS has also been used in many new applications.
GPS determines location by computing the difference between the time that a signal is sent and the time it is received. GPS satellites carry atomic clocks that provide extremely accurate time (see Clocks and Watches: Atomic Clocks). The time information is placed in the codes broadcast by the satellite so that a receiver can continuously determine the time the signal was broadcast. The signal contains data that a receiver uses to compute the locations of the satellites and to make other adjustments needed for accurate positioning. The receiver uses the time difference between the time of signal reception and the broadcast time to compute the distance, or range, from the receiver to the satellite. The receiver must account for propagation delays, or decreases in the signal's speed caused by the ionosphere and the troposphere. With information about the ranges to three satellites and the location of the satellite when the signal was sent, the receiver can compute its own three-dimensional position.
An atomic clock synchronized to GPS is required in order to compute ranges from these three signals. However, by taking a measurement from a fourth satellite, the receiver avoids the need for an atomic clock. Thus, the receiver uses four satellites to compute latitude, longitude, altitude, and time.
GPS comprises three segments: the space, control, and user segments. The space segment includes the satellites and the Delta rockets that launch the satellites from Cape Canaveral, in Florida. GPS satellites fly in circular orbits at an altitude of 20,100 km (12,500 mi) and with a period of 12 hours. The orbits are tilted to the earth's equator by 55 degrees to ensure coverage of polar regions. Powered by solar cells, the satellites continuously orient themselves to point their solar panels toward the sun and their antennas toward the earth. Each satellite contains four atomic clocks.
The control segment includes the master control station at Falcon Air Force Base in Colorado Springs, Colorado, and monitor stations at Falcon Air Force Base and on Hawaii, Ascension Island in the Atlantic Ocean, Diego Garcia Atoll in the Indian Ocean, and Kwajalein Island in the South Pacific Ocean. These stations monitor the GPS satellites. The control segment uses measurements collected by the monitor stations to predict the behavior of each satellite's orbit and clock. The prediction data is uplinked, or transmitted, to the satellites for transmission to the users. The control segment also ensures that the GPS satellite orbits and clocks remain within acceptable limits.
The user segment includes the equipment of the military personnel and civilians who receive GPS signals. Military GPS user equipment has been integrated into fighters, bombers, tankers, helicopters, ships, submarines, tanks, jeeps, and soldiers' equipment. In addition to basic navigation activities, military applications of GPS include target designation, close air support, “smart” weapons, and rendezvous.
With more than 500,000 GPS receivers, the civilian community has its own large and diverse user segment. Surveyors use GPS to save time over standard survey methods. GPS is used by aircraft and ships for en route navigation and for airport or harbor approaches. GPS tracking systems are used to route and monitor delivery vans and emergency vehicles. In a method called precision farming, GPS is used to monitor and control the application of agricultural fertilizer and pesticides. GPS is available as an in-car navigation aid and is used by hikers and hunters. GPS is also used on the Space Shuttle (see Space Exploration: Space Shuttle). Because the GPS user does not need to communicate with the satellite, GPS can serve an unlimited number of users.
GPS is available in two basic forms: the standard positioning service (SPS) and the precise positioning service (PPS). SPS provides a horizontal position that is accurate to about 100 m (about 330 ft); PPS is accurate to about 20 m (about 70 ft). For authorized users—normally the United States military and its allies—PPS also provides greater resistance to jamming and immunity to deceptive signals.
Enhanced techniques such as differential GPS (DGPS) and the use of a carrier frequency processing have been developed for GPS (see Carrier Wave). DGPS employs fixed stations on the earth as well as satellites and provides a horizontal position accurate to about 3 m (about 10 ft). Surveyors pioneered the use of a carrier frequency processing to compute positions to within about 1 cm (about 0.4 in). SPS, DGPS, and carrier techniques are accessible to all users.
The availability of GPS is currently limited by the number and integrity of the satellites in orbit. Outages due to failed satellites still occur and affect many users simultaneously. Failures can be detected immediately and users can be notified within seconds or minutes depending on the user's specific situation. Most repairs are accomplished within one hour. As GPS becomes integrated into critical operations such as traffic control in the national airspace system, techniques for monitoring the integrity of GPS on-board and for rapid notification of failures are being developed and implemented.
As of 2001, 24 GPS satellites were in operation. Replenishment satellites are ready for launch, and contracts have been awarded to provide satellites into the 21st century. GPS applications continue to grow in land, sea, air, and space navigation. The ability to enhance safety and to decrease fuel consumption will make GPS an important component of travel in the international airspace system. Airplanes will use GPS for landing at fogbound airports. Automobiles will use GPS as part of intelligent transportation systems. Emerging technologies will enable GPS to determine not only the position of a vehicle but also its altitude.

GPS menentukan penempatan dengan komputasi perbedaan [itu] antar[a] waktunya yang suatu isyarat dikirim dan waktunya [itu] diterima. GPS satelit membawa jam atom yang menyediakan waktu sangat akurat ( lihat Jam dan [Arloji/Penantian]: Jam Atom). Waktunya informasi ditempatkan siaran kode oleh satelit sedemikian sehingga suatu penerima dapat secara terus-menerus menentukan waktunya isyarat adalah menyiarkan. Isyarat berisi data yang suatu penerima menggunakan untuk menghitung penempatan satelit dan untuk membuat lain penyesuaian yang diperlukan untuk [yang] memposisikan akurat. Penerima menggunakan waktunya perbedaan antar[a] waktunya resepsi isyarat dan waktu siaran untuk menghitung jarak [itu], atau mencakup, dari penerima kepada satelit [itu]. Penerima harus meliputi keterlambatan perkembangbiakan, atau penurunan kecepatan isyarat disebabkan oleh ionospher [itu] dan troposphere [itu]. Dengan informasi tentang cakupan [bagi/kepada] tiga satelit dan penempatan satelit ketika isyarat telah dikirim, penerima dapat menghitung three-dimensional sendiri memposisikan.
Suatu jam atom yang disamakan ke GPS diperlukan dalam rangka menghitung terbentang dari tiga isyarat ini . Bagaimanapun, dengan suatu pengukuran dari suatu satelit keempat, penerima menghindari kebutuhan akan suatu jam atom. Seperti itu, penerima menggunakan empat satelit untuk menghitung garis lintang, garis bujur, ketinggian, dan waktu.

GPS meliputi tiga segmen: [ruang;spasi], kendali, dan segmen pemakai. Segmen [Ruang;Spasi] meliputi satelit [itu] dan Delta meluncur itu meluncurkan satelit [itu] dari Tanjung/Mantol Canaveral, di (dalam) Florida. GPS satelit terbang orbit lingkar pada suatu ketinggian 20,100 km ( 12,500 mi (3)) dan dengan masa 12 jam. Garis edar dimiringkan kepada katulistiwa bumi oleh 55 derajat tingkat untuk memastikan pemenuhan [dari;ttg] daerah kutub. bertenaga mesin Oleh sel matahari, satelit [yang] secara terus-menerus mengorientasi diri mereka untuk menunjuk panel [yang] matahari mereka ke arah matahari dan antena mereka ke arah bumi. Masing-Masing satelit berisi empat jam atom.
Segmen Kendali meliputi stasiun kendali guru [itu] pada Angkatan Udara Burung elang falcon Dasarkan Colorado [Musim semi/ mata air], Colorado, dan setasiun monitor pada Dasar Angkatan Udara Burung elang falcon dan pada [atas] Hawaii, Pulau Kenaikan di (dalam) Samudra Lautan Atlantik, Diego Garcia Pulau karang di (dalam) Lautan India, dan Kwajalein Pulau di (dalam) Lautan Teduh Selatan. Setasiun ini memonitor [itu] GPS satelit. Segmen Kendali menggunakan pengukuran yang dikumpulkan oleh setasiun monitor untuk meramalkan perilaku dari tiap jam dan garis edar satelit. Data Ramalan adalah uplinked, atau dipancarkan, kepada satelit untuk transmisi kepada para pemakai [itu]. Segmen Kendali juga memastikan bahwa [itu] GPS garis edar satelit dan sisa jam di dalam batas bisa diterima.
Segmen Pemakai meliputi peralatan personil militer dan warganegara [siapa] yang menerima GPS isyarat. Militer GPS pemakai peralatan telah terintegrasi ke dalam pejuang, bomber, kapal tangki, helikopter, kapal, kapal selam, tangki/tank, jeep, dan peralatan prajurit. Sebagai tambahan terhadap aktivitas ilmu pelayaran basis dasar, aplikasi militer GPS meliputi tujuan target, menutup pen;dukungan udara,

GPS ada tersedia di (dalam) dua format basis dasar: standard yang memposisikan [jasa;layanan] ( SPS) dan yang tepat memposisikan [jasa;layanan] ( PPS). SPS menyediakan suatu posisi horisontal yang adalah akurat ke sekitar 100 m ( sekitar 330 ft); PPS adalah akurat ke sekitar 20 m ( sekitar 70 ft). Karena [yang] diberi hak users-normally Militer Amerika Serikat dan allies-PPS nya juga menyediakan pembalasan lebih besar [bagi/kepada] menyumbat dan imunitas ke isyarat menipu.
Teknik yang ditingkatkan seperti diferensial GPS ( DGPS) dan penggunaan suatu freknensi pembawa pengolahan telah dikembangkan untuk GPS ( lihat [Gelombang/Lambaian] Pembawa). DGPS mempekerjakan setasiun ditetapkan;perbaiki pada [atas] bumi seperti halnya satelit dan menyediakan suatu posisi horisontal yang akurat ke sekitar 3 m ( sekitar 10 ft). Para pensurvei memelopori penggunaan suatu pengolahan freknensi pembawa untuk menghitung posisi ke di dalam sekitar 1 cm ( sekitar 0.4). SPS, DGPS, dan teknik pengangkut adalah dapat diakses [bagi/kepada] semua para pemakai.
Ketersediaan GPS sekarang ini terbatas oleh nomor;jumlah dan integritas satelit di (dalam) garis edar. Outages dalam kaitan dengan satelit digagalkan masih terjadi dan mempengaruhi para pemakai banyak orang [yang] secara serempak. Kegagalan dapat dideteksi dengan seketika dan para pemakai dapat diberitahu dalam beberapa detik atau beberapa menit yang tergantung pada situasi pemakai spesifik [itu]. Kebanyakan pekerjaan pembetulan terpenuhi di dalam satu jam. [Seperti/Ketika] GPS menjadi terintegrasi ke dalam operasi kritis seperti lalu lintas mengendalikan airspace sistem yang nasional, teknik untuk monitoring integritas GPS diatas kapal dan untuk pemberitahuan kegagalan [yang] cepat dikembangkan dan diterapkan.

Mulai dari 2001, 24 GPS satelit sedang bekerja. Satelit Pengisian kembali adalah siap untuk peluncuran, dan kontrak telah diberikan kepada menyediakan satelit ke dalam abad 21 [itu]. GPS aplikasi melanjut untuk berkembang dalam daratan, laut, udara, dan ilmu pelayaran [ruang;spasi]. Kemampuan untuk tingkatkan keselamatan dan untuk ber/kurang pemakaian bahanbakar akan membuat GPS suatu komponen [yang] penting bepergian airspace sistem yang internasional. Pesawat udara akan menggunakan GPS untuk mendaratkan pada pelabuhan udara terhalang kabut. Mobil akan menggunakan GPS sebagai bagian dari sistem transportasi cerdas. Muncul teknologi akan memungkinkan GPS untuk menentukan tidak hanya posisi suatu sarana (angkut) tetapi juga ketinggian nya.

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