CHENNAI: The final countdown for the launch of India's latest satellite, INSAT-4B, by an Ariane-5 vehicle of Arianespace from Kourou, French Guyana, will begin at 4.25 p.m. on Saturday. If there are no hold-ups in this countdown which will last 11 hours and a half, the launch will take place anytime between 3.55 a.m. and 4.28 a.m. on Sunday.

The indigenously built communication satellite is essentially meant for boosting direct-to-home (DTH) television broadcasting services in India. "After it is made operational, we will have more of dish antennae from roof-tops in our country," said an Indian Space Research Organisation (ISRO) official. The satellite has 24 high-power communication transponders.

Thirty minutes after the lift-off of the launch vehicle, the satellite will be deployed in geo-synchronous transfer orbit (GTO) with a perigee (nearest point to the earth) of 250 km and an apogee of (farthest point from the earth) of 35,886 km. The satellite will reach its final home in a geo-synchronous circular orbit at a height of 36,000 km in phases. This manoeuvre will be done by giving commands from the ground to the liquid apogee motor on the satellite to fire.

ISRO's Master Control Facility (MCF) at Hassan, Karnataka, is ready to take control of the satellite once it is placed in the GTO. In the days after the launch, the MCF will send commands to the satellite to take it to the final destination followed by deployment of its solar panels and antennae. Then the communication payloads on board will be tested.

The satellite, which weighs 3,025 kg, will last 12 years. Built by the ISRO Satellite Centre, Bangalore, it has been provided transponders by the Space Applications Centre, Ahmedabad. The Liquid Propulsion Systems Centre contributed the liquid apogee motors.

Skynet-5A, a communication satellite built by EADS Astrium, is its co-passenger on board the launch vehicle.

Eighteen INSATs have been launched so far, beginning with INSAT-1A from the U.S. on April 10, 1982. The last one, INSAT-4A, was launched by an Ariane vehicle from Kourou on December 22, 2005. Three INSATs — Kalpana, GSAT-2 and Edusat — were launched from Sriharikota using ISRO-built rockets.

The INSATs have brought about a communication revolution in India, enabling people living in far-flung areas to talk to each other over phone.

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