Countdown for the launch of GSLV D 3 has begun at Satish Dhawan Space Centre, Sriharikota. <br/><br/>ISRO spokesman Mr S.Satish said scientists overseeing the pre launch preparations gave the nod for beginning the 29 hour countdown today. <br/><br/>The launch is scheduled at 4.27 p.m today.<br/><br/>AIR Chennai correspondent reports this is the first time India would be using indigenously built cryogenic stage and technology, which is crucial to put communication satellites weighing more than two tonnes in geosynchronous transfer orbit.<br/><br/>Mission Director G. Ravindranath has said despite technology denials, the country has managed to develop cryogenic engine which is the result of 19 years of relentless efforts made by ISRO scientists. <br/><br/>The successful mission would catapult India into the select band of nations including US, Russia, France, Japan and china which have mastered the highest level of propulsion technology. <br/><br/>GSLV D3 would launch GSAT-4, a 2,200 kg experimental satellite, which includes a navigation payload that would offer improved navigation possibilities for civil aircraft. <br/><br/>Another key experiment aboard the mission is the use of a regenerative transponder payload that operates in the advanced Ka frequency band. <br/><br/>ISRO scientists say this is a step forward in the field of communications technology as it will allow for smaller ground terminals at the user end and increase productivity. <br/><br/>GSAT-4 would have a mission life of seven years.<br/>