SATELLITE BASED NAVIGATION SYSTEM 'GAGAN'

To Provide Satellite Based Augmentation System Services over India and neighbouring regions the GPS Aided Geo Augmented Navigation (GAGAN) - a Satellite Based Navigation System (SBNS) is launched by the Union Minister for Civil Aviation, Shri Praful Patel. This system is expected to provide enhanced navigation performance for critical applications like Civil Aviation, Marine Navigation, Train & Road Transport, Precision Farming, Search and Rescue (SAR) operations, Surveying and Mapping (Geodetic & Geodynamic), Mining etc.

GAGAN is a planned implementation of a Satellite Based Navigation System developed by Airports Authority of India (AAI) and Indian Space Research Organisation (ISRO), to deploy and certify an operational SBAS for the Indian Flight Information Region, with expansion capability to neighbouring Flight Information Regions (FIRs). When commissioned for service, GAGAN is expected to provide a civil aeronautical navigation signal consistent with International Civil Aviation Organization (ICAO) Standards and Recommended Practices (SARPs) as established by the Global Navigation Satellite System Panel (GNSSP). ICAO has endorsed Global Navigation Satellite System as Future Air Navigation System (FANS) for civil aviation.

The project involves establishment of a full complement of Satellite Based Augmentation System (SBAS) consisting of 15 Indian Reference Stations (INRES), 3 Indian Navigation Land Uplink Stations (INLUS), 3 Indian Mission Control Centers (INMCC), 3 Geo-stationary Navigation payload in C and L bands and with all the associated Software and Communication links.

Global Positioning System (GPS)

The Global Positioning System (GPS) is a satellite navigation system designed to provide instantaneous position, velocity and time information anywhere on the globe and in its vicinity.

The baseline satellite constellation consists of 24 satellites positioned in six earth-centered orbital planes. The orbital period of a GPS satellite is one-half of a sidereal day or 11 hours 58 minutes. The orbits are nearly circular and equally spaced about the equator at a 60-degree separation with an inclination of 55 degrees relative to the equator. The orbital radius is approximately 26,600 km. With the baseline satellite constellation, users with a clear view of the sky have a minimum of four satellites in view.

Need for Augmentation

• Current GPS constellation cannot support requirements for all phases of flight.
• Integrity is not guaranteed (all satellites are not monitored at all times; time-to-alarm is from minutes to hours, no indication of quality of service).
• Accuracy is not sufficient (even with Selective Availability off, vertical accuracy>10m).
• Availability and continuity must be met.

How GAGAN works

The Global Navigation Satellite System (GNSS) data is received and processed at widely dispersed INRES which are strategically located to provide coverage over the required service volume. Data is forwarded to the INMCC, which process the data from multiple INRES to determine the differential corrections and residual errors for each monitored satellite and for each predetermined ionospheric grid point (IGP). Information from the INMCC is sent to the INLUS and uplinked along with the GEO navigation message to the GAGAN GEO satellite. The GAGAN GEO satellite downlinks this data to the users via two L-band ranging signal frequencies (L1 and L5), with GPS type modulation, to improve the accuracy and availability and provide integrity.

Seamless Coverage

GAGAN will provide augmentation service for GPS over India, Bay of Bengal, South-East Asia, Middle East expanding upto Africa. GAGAN will be compatible and interoperable with other SBAS systems such as the Wide Area Augmentation System (WAAS) of USA, the European Geostationary Navigation Overlay Service (EGNOS) of European Union (EU) and the Multi-functional Satellite Augmentation System (MSAS) of Japan. It will fill the gap between the European EGNOS and the Japanese MSAS to provide seamless air navigation service across regional boundaries.

GAGAN Benefits

To Civil Aviation Sector

• Improved Efficiency/Economy

Ø Direct Routes

Ø Increased Fuel savings

Ø Precision approach at all Runways

Ø Significant cost savings due to withdrawal of ground aids

Ø Reduced workload of Flight Crew and ATCOs

Ø Improved Capacity through reduced aircraft separation

• Higher Accuracy, Global Coverage
• Improved Safety

Ø Controlled Flight into Terrain (CFIT)

Ø Enhanced Air-to-Air Surveillance: ADS-B

Ø Availability of MSAW facility (Min. Safe Altitude Warning)

• Reduced Noise Pollution

To Non-Civil Aviation Sector

• Marine Navigation
• Train & Road transport
• Precision Farming
• Search and Rescue (SAR) operations
• Surveying (Geodetic & Geodynamic)
• Scientific community.