GPS Aided GEO Augmented Navigation

The GPS Aided GEO Augmented Navigation (GAGAN) is an 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.^[2] 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.^[3]

The project has established 15 Indian Reference Stations, 3 Indian Navigation Land Uplink Stations, 3 Indian Mission Control Centers, and installation of all associated software and communication links.^[4] 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 and Leh airports.

Implementation

The ₹7.74 billion (US$121 million) project is being created in three phases through 2008 by the Airport Authority of India with the help of the Indian Space Research Organisation's (ISRO) technology and space support.^[5] 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 was conducted during June 2012 followed by system certification during July 2013.^[5]

Technology

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.^[3] 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.^[6]

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.^[5] 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 behaviour over the Indian region. This has been specially taken up in view of the rather uncertain nature of the behaviour of the ionosphere in the region. The study will lead to the optimisation of the algorithms for the ionospheric corrections in the region.

To study the ionospheric behaviour 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.^[3]

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 center, 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-dimensional 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.

Developments

The first GAGAN transmitter was integrated into the GSAT-4 geostationary satellite, and had a goal of being operational in 2008.^[7][8] 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.^[9]

In 2009, Raytheon had won an 82 million dollar contract. It was mainly dedicated to modernise Indian air navigation system.^[10] 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”^[10]

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.^[11]

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.”^[11]

On 30 December 2013, the Directorate General of Civil Aviation (DGCA), India provisionally certified the GPS Aided Geo Augmented Navigation (GAGAN) system to RNP0.1 (Required Navigation Performance, 0.1 Nautical Mile) service level. The certification enabled aircraft fitted with SBAS equipment to use GAGAN signal in space for navigation purposes.^[12]

Satellites

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.^[5]

GSAT-15 carries 24 Ku band transponders with India coverage beam and a GAGAN payload. was successfully launched on 10 November 2015, 21:34:07 UTC, completing the constellation.

Indian Regional Navigation Satellite System

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 Navigation Satellite System IRNSS.^[13]

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 optimised I-1K structure with a power handling capability of around 1660W and a lift off mass of 1425 kg, and is designed for a nominal mission life of 10 years. The first satellite of IRNSS constellation was launched onboard PSLV (C22) on 1 July 2013. While the full constellation was planned to be realised during 2014 time frame, launch of subsequent satellites got delayed.

Currently all 7 satellites are in orbit but in 2017 it was announced that all three rubidium atomic clocks on board IRNSS-1A had failed, mirroring similar failures in the Galileo constellation. The first failure occurred in July 2016, following which two other clocks also failed. This rendered the satellite somewhat redundant and required replacement. Although the satellite still performs other functions, the data is coarse, and thus cannot be used for accurate measurements. ISRO plans to replace it with IRNSS-1H in July or August 2017.

Two more clocks in the navigational system had started showing signs of abnormality, thereby taking the total number of failed clocks to five.

As a precaution to extend the operational life of navigation satellite, ISRO is running only one rubidium atomic clock instead of two in the remaining six satellites. Each satellite has three clocks, therefore a total of 27 clocks for all satellites in the system (including standby satellites). The clocks of both IRNSS and GALILEO were supplied by SpectraTime. ISRO replaced the atomic clocks in two standby NavIC satellites. The setback comes at a time when IRNSS is yet to start commercial operations.

Applications

Karnataka Forest Department has used GAGAN to build a new, accurate and publicly available satellite based database of its forestlands. This is a followup to the Supreme Court directive to States to update and put up their respective forest maps. The geospatial database of forestlands pilot has used data from the Cartosat-2 satellite. The maps are meant to rid authorities of ambiguities related to forest boundaries and give clarity to forest administrators, revenue officials as also the public, according to R.K. Srivastava, Chief Conservator of Forests (Headquarters).^[14]

Various Indian manufactured missiles including the BrahMos will use GAGAN for guidance.^[15]

See also

• Global Positioning System
• GNSS Augmentation
• Wide Area Augmentation System
• Multi-functional Satellite Augmentation System(MSAS)

References

Further reading

• Rs.378 crore aid for GPS-aided navigation system
• Satellite navigation breakthrough for aircraft and weapons

External links

• ISRO Satellite Navigation Programme