Chennai, Jul 14 (IANS): The 20-hour countdown for the July 15 early morning lift-off of India's heavy rocket nicknamed the 'Bahubali' carrying the Chandrayaan-2 spacecraft began at 6.51 a.m. on Sunday, a top official of the Indian space agency said.

"The countdown started at 6.51 a.m.," K. Sivan, Chairman, Indian Space Research Organisation (ISRO), told IANS.

The 640-tonne rocket Geosynchronous Satellite Launch Vehicle-Mark III (GSLV-Mk III) standing at about 44 metre tall, is nicknamed the 'Bahubali', as like the hero in the successful film lifts a heavy Lingam, the rocket will carry the 3.8-tonne Chandrayaan-2 spacecraft.

About 16-minutes into its flight, the Rs 375 crore GSLV-Mk III rocket is expected to sling the Rs 603 crore Chandrayaan-2 into an Earth parking 170x40400 km orbit.

From there, it will be a long journey for the Chandrayaan-2 spacecraft carrying lander-Vikram and rover-Pragyaan will travel further to the moon.

The distance between earth and the moon is about 3.844 lakh km.

On September 6, the Lander Vikram is expected to make a soft landing on the moon and then Pragyaan will roll out to carry out in-situ experiments.

During the countdown, the rocket and spacecraft's systems will undergo checks and fuel will be filled to power the rocket engines.

To date, ISRO has sent up three GSLV-Mk III rockets.

The first one was on 18.12.2014 carrying Crew Module Atmospheric Reentry Experiment. The second and third GSLV-Mk III went up on 5.2.2017 and 14.11.2018 carrying communication satellites GSAT-19 and GSAT-29 respectively.

Interestingly, GSLV-Mk III will be used for India's manned space mission slated in 2022.