GPS-aided geo-augmented navigation
|Geo-augmented navigation system|
|Type||Regional Satellite-based augmentation system|
|Developers||Indian Space Research Organization
Airports Authority of India
|Accuracy||1.5-metre in the horizontal,
2.5-metre in the vertical
|Orbital Radius||26,600 km (approx)|
|Max operational life||15 years|
|Fully operational by||2013-14|
|Project cost||7.74 billion (US$140 million)|
The GPS aided geo augmented navigation or GPS and geo-augmented navigation system (GAGAN) is a planned implementation of a regional satellite-based augmentation system (SBAS) by the Indian government. It is a system to improve the accuracy of a GNSS receiver by providing reference signals. The AAI’s efforts towards implementation of operational SBAS can be viewed as the first step towards introduction of modern communication, navigation, surveillance/Air Traffic Management system over Indian airspace.
The project involves establishment of 15 Indian Reference Stations, three Indian Navigation Land Uplink Stations, three Indian Mission Control Centers and installation of all associated software and communication links. GAGAN is planned to get into operation by the year 2014. It will be able to help pilots to navigate in the Indian airspace by an accuracy of 3 m. This will be helpful for landing aircraft in tough weather and terrain like Mangalore airport and Leh.
The 7.74 billion (US$142 million) project is being implemented in three phases through 2008 by the Airport Authority of India with the help of the Indian Space Research Organization's (ISRO) technology and space support. The goal is to provide navigation system for all phases of flight over the Indian airspace and in the adjoining area. It is applicable to safety-to-life operations, and meets the performance requirements of international civil aviation regulatory bodies.
The space component will become available after the GAGAN payload on the GSAT-8 communication satellite, which was launched recently, is switched on. This payload was also on the GSAT-4 satellite that was lost when the Geosynchronous Satellite Launch Vehicle (GSLV) failed during launch in April 2010. Final System Acceptance Test will be conducted during June 2012 followed by system certification during July 2013.
To begin implementing a satellite-based augmentation system over the Indian airspace, Wide Area Augmentation System (WAAS) codes for L1 frequency and L5 frequency were obtained from the United States Air Force and U.S Department of Defense on November 2001 and March 2005. The system will use eight reference stations located in Delhi, Guwahati, Kolkata, Ahmedabad, Thiruvananthapuram, Bangalore, Jammu and Port Blair, and a master control center at Bangalore. US defense contractor Raytheon has stated they will bid to build the system.
Technology demonstration 
A national plan for satellite navigation including implementation of Technology Demonstration System (TDS) over the Indian air space as a proof of concept had been prepared jointly by Airports Authority of India (AAI) and ISRO. TDS was successfully completed during 2007 by installing eight Indian Reference Stations (INRESs) at eight Indian airports and linked to the Master Control Center (MCC) located near Bangalore. Preliminary System Acceptance Testing has been successfully completed in December 2010. The ground segment for GAGAN, which has been put up by the Raytheon, has 15 reference stations scattered across the country. Two mission control centres, along with associated uplink stations, have been set up at Kundalahalli in Bangalore. One more control centre and uplink station are to come up at Delhi. As a part of the programme, a network of 18 total electron content (TEC) monitoring stations were installed at various locations in India to study and analyse the behaviour of the ionosphere over the Indian region.
GAGAN's TDS signal in space provides a three-metre accuracy as against the requirement of 7.6 metres. Flight inspection of GAGAN signal is being carried out at Kozhikode, Hyderabad, Nagpur and Bangalore airports and the results have been satisfactory so far.
Study of Ionosphere 
One essential component of the GAGAN project is the study of the ionospheric behavior over the Indian region. This has been specially taken up in view of the rather uncertain nature of the behavior of the ionosphere in the region. The study will lead to the optimization of the algorithms for the ionospheric corrections in the region.
To study the ionospheric behavior more effectively over entire Indian airspace, Indian universities and R&D labs, which are involved in the development of regional based ionotropic model for GAGAN, have suggested nine more TEC stations.
Technology Integration 
GAGAN after its final operational phase completion, will be compatible with other SBAS systems such as the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS) and the Multi-functional Satellite Augmentation System (MSAS) and will provide seamless air navigation service across regional boundaries. While the ground segment consists of eight reference stations and a master control centre, which will have sub systems such as data communication network, SBAS correction and verification system, operations and maintenance system, performance monitoring display and payload simulator, Indian land uplinking stations will have dish antenna assembly. The space segment will consist of one geo-navigation transponder.
Effective flight-management system 
A flight-management system based on GAGAN will then be poised to save operators time and money by managing climb, descent and engine performance profiles. The FMS will improve the efficiency and flexibility by increasing the use of operator-preferred trajectories. It will improve airport and airspace access in all weather conditions, and the ability to meet the environmental and obstacle clearance constraints. It will also enhance reliability and reduce delays by defining more precise terminal area procedures that feature parallel routes and environmentally optimised airspace corridors.
- GAGAN will increase safety by using a three-diemensional approach operation with course guidance to the runway, which will reduce the risk of controlled flight into terrain i.e., an accident whereby an airworthy aircraft, under pilot control, inadvertently flies into terrain, an obstacle, or water.
- GAGAN will also offer high position accuracies over a wide geographical area like the Indian airspace. These positions accuracies will be simultaneously available to 80 civilian and more than 200 non-civilian airports and airfields and will facilitate an increase in the number of airports to 500 as planned. These position accuracies can be further enhanced with ground based augmentation system.
The first GAGAN transmitter was integrated into the GSAT-4 geostationary satellite, and had a goal of being operational in 2008. Following a series of delays, GSAT-4 was launched on 15 April 2010, however it failed to reach orbit after the third stage of the Geosynchronous Satellite Launch Vehicle Mk.II that was carrying it malfunctioned.
In 2009, Raytheon had won a 82 million dollar contract. It was mainly dedicated to modernize Indian air navigation system. The vice president of Command & Control Systems, Raytheon Network Centric Systems, Andy Zogg commented:
“GAGAN will be the world’s most advanced air navigation system and further reinforces India’s leadership in the forefront of air navigation. GAGAN will greatly improve safety, reduce congestion and enhance communications to meet India’s growing air traffic management needs”
In 2012, the Defence Research and Development Organisation received a "miniaturised version" of the device with all the features from global positioning systems (GPS) and global navigation satellite systems (GNSS). The module weighing just 17 gm, can be used in multiple platforms ranging from aircraft (e.g. winged or rotor-craft) to small boats, ships. Reportedly, it can also assist "survey applications". It is a cost-efficient device and can be of "tremendous" civilian use. The navigation output is composed of GPS, GLONASS and GPS+GLONASS position, speed and time data. According to a statement released by the DRDO, G3oM is a state-of-the-art technology receiver, integrating Indian GAGAN as well as both global positioning system and GLONASS systems.
According to Deccan chronicle:
“G. Satheesh Reddy, associate director of the city-based Research Centre Imarat, said the product is bringing about a quantum leap in the area of GNSS technology and has paved the way for highly miniaturised GNSS systems for the future.”
GSAT-8 is an Indian geostationary satellites, which was successfully launched using Ariane 5 on 21 May 2011 and is positioned in geosynchronous orbit at 55 degrees E longitude.
GSAT-10 is envisaged to augment the growing need of Ku and C-band transponders and carries 12 Ku Band, 12 C Band and 12 Extended C Band transponders and a GAGAN payload. The spacecraft employs the standard I-3K structure with power handling capability of around 6 kW with a lift off mass of 3400 kg. GSAT-10 was successfully launched by Ariane 5 on 29 September 2012.
GSAT-15 will carry 24 Ku band transponders with India coverage beam and a GAGAN payload. The satellite is planned to be launched during 2014-15 by Ariane 5. The platform system is based on I-3K satellite.
The Indian government has stated that it intends to use the experience of creating the GAGAN system to enable the creation of an autonomous regional navigation system called the Indian Regional Navigational Satellite System (IRNSS).
IRNSS-1 Indian Regional Navigational Satellite System (IRNSS)-1, the first of the seven satellites of the IRNSS constellation, carries a Navigation payload and a C-band ranging transponder. The spacecraft employs an optimized I-1K structure with a power handling capability of around 1600W and a lift off mass of 1380 kg, and is designed for a nominal mission life of 7 years. The first satellite of IRNSS constellation is planned to be launched onboard PSLV in 2013 while the full constellation is planned to be realized during 2014 time frame. 
See also 
- Global Positioning System
- GNSS Augmentation
- Wide Area Augmentation System
- Multi-functional Satellite Augmentation System(MSAS)
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