There is pressure on the ISRO to produce a winner because of two back-to-back failures of the GSLV flights in 2010 - the first, with an indigenous cryogenic engine, on April 15 and the next, with a Russian cryogenic engine, on December 25.
ISRO's next GSLV flight, with an indigenous cryogenic engine, on August 19, 2013, was called off 75 minutes before lift-off: the liquid fuel from the rocket's second stage had leaked, wetting the first stage and the four strap-on boosters around it. So ISRO dismantled the 49-metre tall vehicle, weighing 415 tonnes and built a refurbished GSLV-D5, with new first and second stages and four new strap-on booster motors.
The Chandrayaan-2 mission, scheduled for 2016, will use a GSLV with an indigenous cryogenic stage. ISRO has to produce two winners in a row with GSLVs with India-built cryogenic stages before it can confidently send up the Chandrayaan-2, which will deploy an India-made lander and rover on the moon.
So Sunday's mission is a crucial one and expectations are, therefore, high from ISRO to deliver. The three-stage GSLV-D5 will put into orbit a 1982-kg communication satellite called GSAT-14.
"We have done our best," K. Radhakrishnan, ISRO Chairman, said on Saturday evening from Sriharikota. "The countdown for the [GSLV-D5] flight began at 11.18 a.m. The rocket's second stage has already been filled with the liquid fuel and oxidiser." Fuel-filling for the four strap-on booster motors began after 6 p.m. "Things are progressing smoothly and the weather is fine," he said.
If the GSLV-D5 mission lasts about 17 minutes, the cryogenic engine itself will fire for a full twelve minutes. At the end of seventeen minutes, the rocket will put the GSAT-14 satellite into orbit. GSAT-14 will be used for telecasting, telecommunication, tele-medicine and tele-education.
The Rs.356 crore launch mission has twin purpose - to flight test the cryogenic engine designed and built by Indian Space Research Organisation (ISRO), and to put in orbit communication satellite GSAT-14.
The rocket port is located about 80 km from Chennai.
The GSLV is a three stage/engine rocket.
This will be the first mission of GSLV in the last four years, after two such rockets failed in 2010. One of the GSLV rockets flew with an Indian cryogenic engine, and the other one with a Russian engine.
The GSLV is a three stage/engine rocket. The first stage is fired with solid fuel, the second with liquid fuel and the third is the cryogenic engine.
The successful flight of this rocket is crucial for India as it will be the first step towards building rockets that can carry heavier payloads of up to four tonnes.
ISRO is planning to launch an upgraded version of GSLV Mark III rocket soon with a dummy payload.
The design payload capacity of GSLV Mark III is four tonnes.
According to ISRO, several design changes had been incorporated in Sunday's rocket after studying the past GSLV rockets and the issues faced in them.
During the countdown to the rocket launch, fuelling of the three stage/engine GSLV rocket's four strap-on motors and the second stage with liquid fuel will be completed, while the first-stage core engine is powered by solid fuel.
The process of fuelling the cryogenic engine will begin around 10 hours prior to the launch.
It is going to be tense 17 minutes for the ISRO scientists Sunday after the 49.13 metre tall rocket weighing 414.75 tonnes blasts off at 4.18 p.m., till the GSLV rocket safely delivers GSAT-14 to augment the Indian transponder capacity.
(With agency inputs)