BENGALURU: The Indian Space Research Organisation (ISRO) on Tuesday successfully tested its indigenous cryogenic engine for 635 seconds, the full duration of an actual flight. A successful cryogenic engine will let India launch 4-tonne satellites — the INSATs — into geostationary orbit.These satellites are the backbone of India’s communications, weather forecasting, broadcasting and other applications. Tuesday’s test is the fifth ground test of the cryogenic engine.Earlier tests were of short duration of 10-20 seconds. When ready, ISRO will use this engine as the upper stage of the heavy lifter GSLV Mark III . This vehicle is ready and has had a short flight last year, but is waiting for the cryogenic engine for a full flight.There are several tests to be done before the engine can integrate with the rocket, but it has crossed a major hurdle on Tuesday. This means that the technology has been achieved and the design is sound,” says K Sivan, director of the ISRO Liquid Propulsion Centre (LPSC)in Trivandrum.ISRO’s Mark III version of Geostationary Launch Vehicle is being developed to carry fourtonne class satellites into geostationary orbit. This would mean that the country can launch large weather and communication satellites on its own, while also offering cheap launch services to others.