Chennai, Aug 27 (IANS): The countdown for the launch of India's heavy rocket geosynchronous satellite launch vehicle-D6 (GSLV-D6) carrying communication satellite GSAT-6 with strategic use progressed smoothly on Thursday at Sriharikota rocket port in Andhra Pradesh, Indian space agency said.

The countdown began at 11.52 a.m. on Wednesday.

According to Indian Space Research Organisation (ISRO), the preparations for fuelling up the cryogenic engine is under progress.

On Monday, ISRO's Mission Readiness Review Committee and the Launch Authorisation Board (LAB) cleared the launch on Thursday evening.

The communication satellite will be launched with ISRO's heavier rocket GSLV.

The 49.1 metre tall and weighing 416 tonne GSLV rocket will blast off at 4.52 p.m. from the second launch pad.

Seventeen minutes into the flight the rocket will put into orbit the GSAT-6 communication satellite weighing 2,117 kg.

This is the fifth time ISRO is flying a GSLV rocket carrying a satellite weighing over two tonne.

Out of the four earlier rocket missions with over two tonne satellites, three failed due to various reasons and one was successful.

The GSLV is a three stage/engine rocket has a total carrying capacity of around 2.2 tonne. The first stage is fired with solid fuel, the second with liquid fuel and the third is the cryogenic engine.

Indian space agency is flying the GSLV rocket with its own cryogenic engine for the second time on Thursday after the successful launch of similar rocket in January 2014 that put into orbit GSAT-14.

A cryogenic engine is more efficient as it provides more thrust for every kilogram of propellant burnt.

The satellite GSAT-6 is India's 25th geostationary communication satellite and 12th in the GSAT series.

Five of GSAT-6's predecessors were launched by GSLV during 2001, 2003, 2004, 2007 and 2014 respectively.

After its commissioning, GSAT-6 will join the group of India's other operational geostationary satellites.

The satellite provides communication through five spot beams in S-band and a national beam in C-band for strategic users.

The cuboid shaped GSAT-6 has a lift-off mass of 2,117 kg. Of this, propellants weigh 1,132 kg and the dry mass of the satellite is 985 kg.

One of the advanced features of GSAT-6 satellite is its S-Band Unfurlable Antenna of six metre diameter.

This is the largest satellite antenna realised by ISRO. This antenna is utilised for five spot beams over the Indian main land.

The spot beams exploit the frequency reuse scheme to increase frequency spectrum utilisation efficiency.

The satellite's life expectancy is nine years.