ISRO (Indian Space Research Organisation) so far never before used additional marine vessels to help track their launch vehicles, as an extension to the Indian Deep Space Network (IDSN). So why did it require additional tracking stations in the South Pacific for the launch of the PSLV C25 (Polar Satellite Launch Vehicle) on its Magalyaan / Mars Orbiter Mission (MOM)?
Wikipedia writes to say about the MOM tracking and command:
The Indian Space Research Organisation Telemetry, Tracking and Command Network performed navigation and tracking operations for the launch with ground stations at Sriharikota, Port Blair, Brunei and Biak in Indonesia, and after the spacecraft's apogee becomes more than 100,000 km, two large 18-metre and 32-metre diameter antennas of the Indian Deep Space Network will be utilised.
NASA's Deep Space Network will provide position data through its three stations located in Canberra, Madrid and Goldstone on the U.S. West Coast during the non-visible period of ISRO's network. Additional monitoring is provided by technicians on board two leased ships from Shipping Corporation of India, SCI Nalanda and SCI Yamuna which are currently in position in the South Pacific near Fiji.
How did they track their previous launchers, like e.g. Chandrayaan-1, without these additional tracking stations, and why was this extension to the IDSN necessary for Magalyaan, if they already used NASA's Deep Space Network with facilities in Canberra, Australia?