Introduction
Since the beginning of time, human beings have looked to the sky to determine their whereabouts. Traditionally, the Sun and the pattern of fixed stars have been their guides. But in the second millennium, constellations of man-made satellites have taken over as beacons to guide the way.
What is satellite navigation?
Using the fixed stars, you can determine your position anywhere on the Earth’s surface to within a few hundred meters provided the weather is fine. But navigation satellites can tell you where you are to the nearest few meters or better, whatever the weather. Enhanced instruments can even pinpoint the position of a stationary object to within a few centimeters by measuring the object’s position many thousands of times over several hours and then working out the average of the measurements. Sophisticated new receiver technology picks up signals transmitted by navigational satellites. The receiver technology is small enough to be incorporated into the electronics of a car or mobile phone, and all our lives are changing as a result.
A satellite navigation is a system of satellites that provide autonomous geo-spatial positioning with global or regional coverage. The signals also allow the electronic receivers to calculate the current local time to high precision, which allows time synchronisation. A satellite navigation system with global coverage may be termed a global navigation satellite system or GNSS.
American Global Positioning System (GPS) technology is widely available for vehicles and smartphones. GPS was originally developed in the United States for defense related applications, way back in the 1970s, GPS services became available to civilians in the 1990s. The technology is based on the user's receiver picking up precisely timed radio signals from orbiting satellites, and calculating its distance from each source. Since the signals also communicate the position of each satellite in its orbit, the device can combine the information to pinpoint the location of the user in three dimensions. The precise time signals from the constellation of satellites - 32 in total for GPS - can also provide accurate time and synchronization data for mobile phones and networks.
Some of the major Satellite Navigation Systems are the Global Positioning System (US), GLONASS (Russia), Galileo (Europe), Indian Regional Navigation Satellite System (IRNSS), Quasi-Zenith Satellite System (Japan), Doppler Orbitography and Radio-positioning Integrated by Satellite-DORIS (France) and BeiDou-2 (China).
Indian Regional Navigation Satellite System (IRNSS)
Satellite Navigation service is an emerging satellite based system with commercial and strategic applications. ISRO is committed to provide the satellite based Navigation services to meet the emerging demands of the Civil Aviation requirements and to meet the user requirements of the positioning, navigation and timing based on the independent satellite navigation system. To meet the Civil Aviation requirements, ISRO is working jointly with Airport Authority of India (AAI) in establishing the GPS Aided Geo Augmented Navigation (GAGAN) system. To meet the user requirements of the positioning, navigation and timing services based on the indigenous system, ISRO is establishing a regional satellite navigation system called Indian Regional Navigation Satellite System (IRNSS).
(a) GPS Aided GEO Augmented Navigation (GAGAN):
This is a Satellite Based Augmentation System (SBAS) implemented jointly with Airport Authority of India (AAI). The main objectives of GAGAN are to provide Satellite-based Navigation services with accuracy and integrity required for civil aviation applications and to provide better Air Traffic Management over Indian Airspace. The system will be interoperable with other international SBAS systems and provide seamless navigation across regional boundaries. The GAGAN Signal-In-Space (SIS) is available through GSAT-8 and GSAT-10.
(b) Indian Regional Navigation Satellite System (IRNSS)
This is an independent Indian Satellite based positioning system for critical National applications. The main objective is to provide Reliable Position, Navigation and Timing services over India and its neighbourhood, to provide fairly good accuracy to the user.
IRNSS will provide basically two types of services:
- Standard Positioning Service (SPS)
- Restricted Service (RS)
Space Segment consists of seven satellites, three satellites in GEO stationary orbit (GEO) and four satellites in Geo Synchronous Orbit (GSO) orbit with inclination of 29° to the equatorial plane. All the satellites will be visible at all times in the Indian region. The first satellite is scheduled to be launched in 2013 and the total seven satellite constellation is scheduled to be in place by 2016. Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. It provides the monitoring of the constellation status, computation of the orbital and clock parameters and navigation data uploading. The Ground segment comprises of TTC & Uplinking Stations, Spacecraft Control Centre, IRNSS Timing Centre, CDMA Ranging Stations, Navigation Control Centre and Data Communication Links. Space segment is compatible with single frequency receiver for Standard Positioning Service (SPS), dual frequency receiver for both SPS & RS service and a multi mode receiver compatible with other GNSS providers.
Some applications of IRNSS are:
- Terrestrial, Aerial and Marine Navigation
- Disaster Management
- Vehicle tracking and fleet management
- Integration with mobile phones
- Precise Timing
- Mapping and Geodetic Data Capture
- Terrestrial navigation aid for hikers and travellers
- Visual and voice navigation for drivers
Courtesy of IDN
