Isro to Test-Fly Heaviest Rocket, Crew Module on December 18

India will test-fly its heaviest and upgraded rocket - the Geosynchronous Satellite Launch Vehicle (GSLV-Mark III) - on December 18, space agency Isro said Friday.

According to a tweet by the Indian Space Research Organisation (Isro), the 630-tonne rocket will be powered by liquid and solid fuel engines while the cryogenic stage/engine will be a passive one.

The rocket will also carry a crew module to test its re-entry characteristics.

"The main purpose of the mission is to test the atmospheric characteristics and stability of the rocket on its way up. We also decided to use this opportunity to test one component of the crew module - a human space mission that India may embark on at a later date," M.Y.S Prasad, director of the Satish Dhawan Space Centre in Sriharikota, told reporters in a recent interaction.

The experimental mission will cost Rs. 155 crores and will not carry any satellite as the cryogenic engine needed for the purpose is still under development, he said.

(Also See: Isro's GSAT-16 Communications Satellite Launched Successfully Into Orbit)

"The cryogenic engine is under development and will take more two years to be ready," he said.

As the other rocket engines are ready, Isro decided to go ahead with this mission.

"This will be India's new launch vehicle. It is bigger and can carry satellites up to four tonnes," said GSLV Mark III project director S. Somanath.

As for the crew module, it will not carry any living being and is only for study purposes.

The main objective of the crew module is to demonstrate its re-entry flight and aero braking, and end-to-end parachute system validation.

The rocket will go up to 126km and the crew capsule will then detach and fall into the Bay of Bengal, 20 minutes after blast-off.

The descent speed of the crew module will be controlled on board motors for some distance and then by three parachutes.

The module will splash down 600km from Port Blair and 1,600km from the space centre. The capsule will be recovered by an Indian Coast Guard or Indian Navy ship.

The crew module, looking like a giant-size cup cake - black on top and brown at the bottom - weighs around four tonnes. According to an Isro official, it will be in the size of a small bedroom and can accommodate 2-3 people.