Navigation Satellites

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navigation satellite
One of Galileo's satellite

Navigation Satellite or Satellite Navigation or SatNav system provides real-time information regarding latitude, longitude, elevation and attitude (Geospatial Data) of a geographic location or an object autonomously using satellites.

The first satellite navigation system was Transit launch by United States in 1960’s.

Satellite Navigation uses group of satellites termed as Constellations to cover the entire earth surface (Globe).

Google Maps use satellite navigation to help us precisely locate our position.

A Satellite Navigation system with global coverage is termed as GNSS (Global Navigation Satellite System)

There are only 4 GNSS as of December 2016, They are

1. GPS – Global Positioning System – USA

2. GLONASS– Global Navigation satellite system – Russia

3. BDS/BeiDou-2 (formerly known as Compass) – BeiDou Navigation Satellite System – China – Fully Operational by 2020

4. GPS – Galileo Positioning System- European Union (EU) and European Space Agency (ESA) – Fully Operational by 2020

Not be confused with Global Positioning System.

A Typical Global Navigation Satellite System uses 18-30 MEO (Medium Earth Orbit) satellites moving in various orbital planes to cover the entire globe.

Constellation of Satellites around the Globe

Read About Introduction to Orbits

These satellites (MEO’s) make an orbital inclination of 50° at an altitude of 20,000 km and orbital period of roughly 12 hours.

United States, GPS (Global Positioning System) is the most widely used GNSS worldwide.

Read About GNSS

Augmentation system

GNNS Augmentation is a method of improving the navigation system attributes namely accuracy, reliability and availability.

Following are the augmentation systems used by different countries.

GANAN ( GPS Aided GEO Augmented Navigation ) – India

WAAS ( Wide Area Augmenetation System )- United States

EGNOS ( European Geostationary National Overlay Service) – Europe

MSAS (Multi-Functional Satellite Augmentation System) – Japan

Classification 

Satellite Navigation System is classified as follows

1. GNSS -1 – It is a Satellite Navigation System with a combination of GPS and GLONASS with SBAS (Satellite Based Augmentation System) and Ground Based Augmentation System.

2. GNSS -2 – Second Generation of Satellite System

3. Core Satellite Navigation System – combination of GPS, GLONASS, Galileo and Compass

4.Satellite based Augmentation System – Ominstar and Starfire

5. Regional SBAS including WAAS (US), EGNOS (EU), MSAS (Japan) and GAGAN (India).

SBAS – Satellite Based Augmentation System

6. Regional Satellite Navigation SystemNAVIC, QZSS, Beidou

7. Continental Scale Ground Based Augmentation System (GBAS) – DGPS (Differential GPS)

8. Regional Scale GBAS- CORS

9. Local GBAS

Miscellaneous Facts

Satellites use Atomic clocks to maintain synchronization of all satellites in the constellation.

Read About Atomic Clocks

GPS uses triangulation to get real time data using 3 or 4 satellites.

Satellite constellation of GPS consists of 24 satellites positioned in six earth-centered orbital planes with four operation satellites.

The orbital period of a GPS satellite is 11 hours 58 minutes or half sidereal day.

The orbital radius of a GPS satellite is approximately 26,600 km.

Effective visibility angle of GPS satellites on the Earth’s surface.