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Satellite navigation, GPS

Satellite navigation, GPS

The Global Positioning System consists of 24 satellites but only 4 have to be visible for positioning.

Geography

Keywords

satellite navigation, satellite, navigation, GPS, Global Positioning System, positioning, distance measurement, elevation, civil, military, geography

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Scenes

Narration

Initial developments of the Global Positioning System (GPS) were launched during the Cold War for military purposes. In 1983, the Soviet Union shot down a South Korean civilian airliner entering their airspace.
To prevent such a tragedy ever happening again, U.S. President Ronald Reagan ordered the development of a system that would be made available for civilian use.
The first satellite in the Global Positioning System was launched in 1989, its twenty-fourth satellite in 1993. GPS satellites orbit 20,200 km (12,550 mi) above the Earth on six tracks.

Positioning is done by triangulation; the receiver determines the satellite’s distance based on the signals it has emitted. The first satellite draws a circular arc on the Earth’s surface. Every point of this arc is located at the same distance from the receiver.
A second satellite draws another circular arc; the receiver is found somewhere in the intersection of these two arcs. The position of the receiver can be precisely determined by using a third satellite.
In practice, a fourth satellite is required to measure elevation for a greater accuracy of measurement.

Distance measurement is based on the following principle; the signal emitted by the satellite encodes the time of emission, which the receiver compares with the time of reception. After that, it calculates the time it took for the signal to arrive.
The signal travels at the speed of light, at almost 300,000 kilometers per second (186,400 miles per second). For instance, if 0.1 seconds have elapsed between the emission and reception of the signal, the distance is approximately 30,000 kilometers (18,640 miles).
In practice, the process of calculation is more complicated, since according to Albert Einstein’s theory of relativity, time is affected by motion.

Today inexpensive GPS receivers are available to anyone. Most mobile phones also contain GPS receivers.
In addition to civilian use, military use is also highly important, since in modern warfare, great accuracy is essential for minimizing civilian casualties.
High-tech missiles and cruise missiles can continuously measure their positions and are able to adjust their trajectory accordingly.

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Geographic coordinate system

The geographic coordinate system enables every location on the Earth to be exactly specified.

Geographic coordinate system (basic)

The system of circles of latitude and longitude on the globe enable every location on the Earth to be exactly specified.

How does it work? - Cell phone

This animation demonstrates how cell phones work.

Hubble Space Telescope

The Hubble Space Telescope orbits outside the distorting influence of Earth´s atmosphere.

ISS

The International Space Station is a habitable satellite built with the cooperation of 16 countries.

Mars Exploration Program

Space probes and Mars rovers examine the structure of Mars and possible traces of life.

Measuring time

The first calendars and time-measuring instruments were already used by ancient Eastern civilizations.

Moon landing: July 20, 1969

Neil Armstrong, one of the crew members of Apollo 11 was the first man to set foot on the Moon.

Navigational instruments of the past

Several ingenious instruments have been invented over the centuries to help in navigating the seas.

Satellite types

Satellites orbiting the Earth can be used for civilian or military purposes.

Space Shuttle

The Space Shuttle was a manned, reusable spacecraft operated by NASA.

Structure of the Earth (intermediate)

The Earth is composed of several spherical layers.

The Earth’s magnetic field

The Earth’s magnetic North and South poles are located near the geographic North and South poles.

Unmanned aerial vehicles (UAV)

The range of applications of unmanned aerial vehicles ('drones') keeps growing.

Voyager space probes

The Voyager space probes were the first man-made objects to leave the Solar System. They gather data about outer space and carry information about humanity.

Yuri Gagarin’s journey to outer space (1961)

Yuri Gagarin became the first human in space on April 12, 1961.

How does it work? - Computer networks

The Internet allows us to send data quickly to large distances.

Sputnik 1 (1957)

The Soviet-made satellite was the first spacecraft to be launched into outer space (in October 1957).

Lighthouse

Lighthouses are used as an aid to navigation in coastal waters.

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