The 25-and-half hour countdown for GSLV MK III began yesterday at 3.58 pm and was "progressing normally". Scientists were currently involved in the propellant filling operations of the heaviest GSLV-Mk III D1, officials said.
The rocket is scheduled for a lift off at 5.28 pm from second launch pad at the Satish Dhawan Space Centre, Sriharikota about 120 kms from here.
Till now, ISRO had to depend on foreign launchers for communication satellites weighing more than 2,300 kg. The GSLV Mk III D1 is capable of lifting payloads of up to 4,000 kg into the Geosynchronous Transfer Orbit (GTO) and 10,000 kg into the Low Earth Orbit.
ISRO Chairman A S Kiran Kumar had said the mission is important as "it was the heaviest-ever rocket and satellite to be launched from the country".
GSLV Mk III D1 is capable of lifting payloads (or satellites) of upto 4,000kgs into the Geosynchronous Transfer Orbit (GTO) and 10,000kg into the Low Earth Orbit.
Earlier, ISRO had launched the 3,404 kg GSAT-18 communication satellite from Ariane, French Guiana.
The GSLV-Mk III-D1 is a three-stage vehicle with indigenous cryogenic upper stage engine designed to carry heavier communication satellites into the GTO.
Today's mission would augment India's communication resources as a single GSAT-19 satellite will be equivalent to having a constellation of six to seven of the older variety of communication satellites.
In 2014, ISRO had successfully tested the Crew module Atmospheric Reentry experiment with the flight GSLV Mk III.
The module after making its re-entry deployed its parachutes as planned and splashed down in the Bay of Bengal.