The countdown for the lift-off of the Geo-synchronous Satellite Launch Vehicle (GSLV-F06) from Sriharikota on Saturday at 4.04 p.m. has begun.

The countdown, which began at 10.04 a.m. on Friday, was coasting along without any interruption, Indian Space Research Organisation (ISRO) officials said. The GSLV-F06 will put in orbit communications satellite GSAT- 5P that weighs 2,310 kg.

“Everything is fine. The countdown is on without any hitch. The pre-countdown activities too went on well,” said ISRO spokesman S. Satish. The GSLV-F06 is a three-stage rocket and solid propellants drive the core first stage.

Mr. Satish said the important activities that would happen during the 30-hour countdown included filling the second stage and the strap-on booster motors around the first stage with liquid propellants and pumping liquid oxygen and liquid hydrogen into the third upper cryogenic stage, which is imported from Russia.

The second stage was filled with fuel, ISRO officials said from Sriharikota around 2.45 p.m. on Friday. The fuelling of the strap-on booster motors would begin by 7 p.m. and last till midnight. The cryogenic stage would start receiving liquid hydrogen at minus 253 degrees Celsius and liquid oxygen at minus 183 degrees Celsius from 10 a.m. on Saturday.

The launch was to originally take place on December 20 but a leak of helium gas from a valve in the cryogenic stage delayed the lift-off. The leak was above the acceptable limit. ISRO's rocket engineers, in tandem with the Russian cryogenic specialists, battled the leak for four days and brought it under control. Helium gas pushes the liquid hydrogen and liquid oxygen out of their chambers in the cryogenic stage before they are ignited.

The ISRO officials stressed that cryogenic engines were a class apart in terms of their complexity and performance. Of all types of propulsion, cryogenic technology is the most complex to develop. A cryogenic engine is essential to put heavy communication satellites, weighing above 2,000 kg, in geo-synchronous transfer orbit.

The GSLV-F06 is 51 metres tall and weighs 418 tonnes – two metres taller and weighing four more tonnes than its predecessors. The GSAT-5P will be used for broadcasting television programmes, beaming telephone conversations and networking banking transactions.

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