M.V.S. Prasad
With the launch of IRNSS-1A satellite, India has joined a select group of nations with indigenously developed navigation systems. India’s first dedicated navigational satellite the IRNSS-1A developed by the ISRO was successfully put into orbit on the night of 1st July 2013.This is the first of the seven satellites of the Indian Regional Navigation Satellite System (IRNSS).
Overview of Indian Regional Navigation Satellite System (IRNSS)
IRNSS is an Independent regional navigation satellite system being developed by India. It is designed to provide accurate position information service to users in India as well as the region extending up to 1500 Km from its boundary, which is its primary service area. The Extended Service Area lies between primary service area and area enclosed by the rectangle from Latitude 30 degree South to 50 degree North, Longitude 30 degree East to 130 degree East.
IRNSS will provide two types of services, namely, Standard Positioning Service (SPS) which is provided to all the users and Restricted Service (RS), which is an encrypted service provided only to the authorized users. The IRNSS System is expected to provide a position accuracy of better than 20 metres in the primary service area.
IRNSS consists of a space segment and a ground segment. The IRNSS space segment consists of seven satellites, with three satellites in geostationary orbit and four satellites in inclined geosynchronous orbit. Thus, IRNSS satellites revolve round the earth at the height of about 36,000 km from the earth’s surface.
IRNSS ground segment is responsible for navigation parameter generation and transmission, satellite control, ranging and integrity monitoring and time keeping.
Applications of IRNSS include land, sea and air navigation, disaster management, vehicle tracking and fleet management, integration with mobile phones, provision of precise time, mapping, navigation aid for hikers and travelers, visual and voice navigation for drivers. It can track people or vehicles and can be of immense use in disaster situations like the recent one in Uttarakhand. Even the Railways may find it useful to track its wagons. Apart from India, its benefits would extend to a range of 1500 km in the region.
IRNSS-1A
The satellite is based on ISRO’s I1K satellite bus and has two solar panels with Ultra Triple junction solar cells that together generate about 1660 Watts of electrical power. A rechargeable Lithium ion battery of 90 Ampere-Hour capacity is also part of the power system of the satellite. Sun and Star sensors as well as gyroscopes provide orientation reference for IRNSS-1A. Special thermal control schemes have been designed and implemented for some of the critical elements such as atomic clocks of the satellite.
The Attitude (orientation) and Orbit Control System (AOCS) of IRNSS-1A maintains the satellite’s orientation and its propulsion system consists of a Liquid Apogee Motor (LAM) and 12 thrusters. After injection into the circular geosynchronous orbit, the satellite will be located at 55 degrees East longitude with an inclination of 29 degrees with respect to the equator. The mission life of IRNSS-1A is about ten years.
IRNSS-1A was built at ISRO Satellite Centre, Bangalore with important contributions from VSSC, LPSU, IISU and Laboratory for Electro-Optics Systems (LEOS). The payloads of IRNSS-1A were developed by Space Applications Centre (SAC), Ahmedabad.
Payloads
IRNSS-1A carries two types of payloads – a navigation payload and a ranging payload. The navigation payload of IRNSS-1A will transmit navigation service signals to the users. This payload will be operating in 1.5 band (1176.45 MHz) and S band (2492.028 MHz). A highly accurate Rubidium atomic clock is part of the navigation payload of the satellite.
The ranging payload of IRNSS-1A consists of a C-band transponder which facilities accurate determination of the distance to the satellite (ranging). IRNSS-1A also carries Corner Cube Retro Reflectors for laser ranging.
The other mission, launch of IRNSS 1B navigational satellite will be decided based on the performance and in-orbit testing of IRNSS-1A.
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