"The 56 hours and 30 minutes countdown started as per schedule at 06.08 am. It is proceeding smoothly," a spokesman of the Indian Space Research Organisation said.
ISRO's workhorse launch vehicle PSLV C25, carrying India's first inter-planetary satellite Mars Orbiter Mission, is scheduled to lift off at 2.38 pm on November 5 from the spaceport of Sriharikota, nearly 100 km from Chennai.
The Launch Authorisation Board had on November 1 given its consent for the launch of the MOM after the successful conduct of a launch rehearsal the previous day.
The rocket is expected to take over 40 minutes to inject the satellite into Earth's orbit after the take off.
The vehicle tracking stations at Port Blair, Bylalu near Bangalore, Brunei and sea-borne terminals on board Shipping Corporation of India's vessels SCI Nalanda and SCI Yamuna positioned at South Pacific Ocean have also been kept on alert, ISRO sources said.
Once launched, the satellite is expected to go around the Earth for 20-25 days, before embarking on a nine-month voyage to the red planet on December 1 and reach the orbit of the Mars on September 24, 2014.
If India succeeds in the Rs 450-crore MOM mission, it would be the fourth country in the world, after the Unites States, Russia and Europe to do so.
European Space Agency of European consortium, National Aeronautics and Space Administration of the US and Roscosmos of Russia are the three agencies which have successfully undertaken missions to the red planet so far.
Though there have been 51 missions to the Mars, only 21 of them have been successful.
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