PSLV-C17, Indian Space Research Organisation's workhorse Polar Satellite Launch Vehicle, would lift-off from the Satish Dhawan Space Centre at Sriharikota, 90 km from here, with the launch window scheduled between 4.48 p.m. and 5.08 pm.
"The countdown which began yesterday at 11.48 am is progressing smoothly. The vehicle is expected to lift off at 4.48 p.m from the second launch pad," ISRO spokesperson S Satish said.
All mandatory checks were progressing smoothly, he said adding PSLV-XL, a more powerful version of the rocket, would be used for the launch.
GSAT-12, weighing 1,410 kg and equipped with 12 Extended-C band transponders, will augment communication capabilities in telemedicine, tele-education and telephone and other services.
ISRO Chairman K Radhakrishnan said "the countdown has already started and we expect the rocket to lift off at 4.48 pm." In PSLV-XL version, six extended solid strap-on motors carrying 12 tonnes of solid propellant in total are being used as against nine tonnes in a standard PSLV variant, he said.
This is the second time such a powerful configuration had been deployed, after it was used to put Chandrayaan-I into orbit in 2008.
For the PSLV, this will be the 19th mission with the last 17 flights proving successful. This is the second PSLV launch this year after the PSLV-C16 in April when the rocket lofted Resourcesat-2 and two other micro satellites into orbit.