Indian Space Research Organisation is all set for one of its most ambitious tests as it readies for the unique maiden flight today of its heaviest rocket till date -- the 630-tonne, three-stage rocket Geo-Synchronous Satellite Launch Vehicle Mark III.

The Mission Readiness Review and the Launch Authorisation Board,
 has cleared the launch for December 18 at 9.30 a.m., it said.

A senior ISRO official explained that the lesser duration of the countdown for the mission was due to the dummy cryogenic stage. As per the plan, soon after the lift-off at Sriharikota, ISRO would study the flight validation of the complex atmospheric flight regime of LVM 3 and would also test the ability of the CREW module to re-enter the Earth's atmosphere with thermal resistance, parachute deployment in cluster formation, aero braking system and apex cover separation procedures.