The countdown for Monday's Chandrayaan-2 mission launch will start at 6.43 p.m. today, ISRO chairman K. Sivan has said. The rocket and spacecraft's systems will undergo checks and fueling during the countdown.The GSLV-Mk III rocket with Chandrayaan-2 spacecraft was originally scheduled for flight at 2.51 a.m. on July 15. However, the flight was postponed after a technical snag was detected an hour prior to the rocket lift-off. ISRO later rectified the fault in its 44-metre Geosynchronous Satellite Launch Vehicle-Mark III (GSLV-Mk III). Weighing about 640-tonne, the GSLV-Mk III rocket is nicknamed 'Bahubali' after the hero of a successful film of the same name. Just like the protagonist of the film lifted a heavy Lingam in one of its scenes, 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 its 170x40400-km orbit.ISRO has sent up three GSLV-Mk III rockets so far. The first carried Crew Module Atmospheric Re-entry Experiment in December 2014. The second and third GSLV-Mk III carried communication satellites GSAT-19 and GSAT-29 in February 2017 and November 2018 respectively.GSLV-Mk III will also be used for India's manned space mission in 2022.