The Centre for Asia Pacific Aviation reports that the Government of India has approved the Airports Authority of India (AAI) and Indian Space Reseach Organisation’s (ISRO) proposal for the implementation of the GPS Aided Geo Augmented Navigation (GAGAN) project for seamless navigation over Indian airspace at an estimated cost of INR 7.74 Billion.
Ex-post facto approval has also been given to the amount of INR 1.48 Billion already spent in the first phase of the project. With GAGAN, India will be only the fourth country in the world to have a satellite based navigation system.
The management of airspace, a sovereign function, has been assigned to the AAI. The AAI presently uses ground based terrestrial navigation system for providing safe navigation over the Indian airspace. The ground based system has site limitations and range problems.
To overcome the limitations of ground based navigation systems, in 1993, the International Civil Aviation Organisation (ICAO) endorsed use of a Global Satellite Navigation System as a future Air Navigation System for Aviation. Following this, the AAI and ISRO entered into an MoU in 2001 for the implementation of the GAGAN project for seamless navigation over Indian airspace.
The United States has put in place a Global Positioning System (GPS) using 29 satellites at an altitude of 20,000 km orbit. However, the position accuracies required for precision approach and landing, for Civil Aviation, cannot be met by the core GPS constellation, due to the uncertainties in the position accuracies caused by Ionospheric delays, satellite ephemeris and clock errors. The constellation needs to be augmented to provide higher accuracy, reliability and integrity, with the help of a Space Based Augmentation System (SBAS).
In order to provide enhanced accuracies with integrity, reliability and continuity, it is essential to have an augmentation system capable of collecting data in two frequencies over the service area, separate these errors at the master control centre and communicate and correct message to the aviation user in the frequency as that of the core GPS.
To achieve this, an SBAS consisting of a geo-stationary space segment for the core constellation, a ground segment consisting of reference stations, the master control centre and an uplink earth station are required. The reference stations collect dual frequency data, which is communicated to the master control centre. At the master control centre, the errors are separated and the corrected navigation message is sent to the navigation transponder on board the geo stationary satellite, which translates it to the user GPS civil frequency. The GAGAN system proposes to augment the GPS data with the help of a geo stationary satellite to be launched by ISRO and the ground based infrastructure of reference stations, uplink earth stations and master control center created by the AAI.
The implementation of the GAGAN programme is being realized in two phases:
- GAGAN TDS phase (Technology Demonstration System) – to develop and demonstrate the technological capability. This phase was successfully tested and completed in August 2007.
- GAGAN FOP (Final Operation Phase) – to be implemented for operational use and to be certified by DGCA. This phase is expected to be completed by May 2011.
INR 1.48 Billion has already been spent in the TDS phase and the balance INR 6.26 Billion is to be spent in the FOP phase. Of this, the AAI contribution is expected to INR 5.96 Billion, from its internal resources, and ISRO’s contribution will be INR 1.78 Billion, from ISRO budget. The AAI has already spent INR 1 Billion and ISRO INR 480 million in the TDS phase.