ISRO sources said the launch of Insat-3B had been advanced to precede that of Insat-3a, the first of the third generation satellites, to quickly augment the extended C-band capacity of the Insat system.

Insat-3B would provide fixed satellite service (FSS) in extended C-band and Ku-bands and mobile satellite services (MSS) in S-band.

ISRO had planned to launch the satellite, weighing about 2,000 kg later this year.

It would generate about 1,650 mw of power from a double-sided solar array configuration, they said.

ISRO said work on Insat-3A and Insat-3C has also commenced. Insat-3A would be a multi-purpose satellite providing communication, meteorological and search and rescue services.

It would provide normal C-band, extended C-band andKu-band FSS communication services, meteorological services through very high resolution radiometer (VHRR) and charged coupled device (CCD) camera systems.

ISRO said Insat-3A also carries a meteorological data relay transponder (DRT) as well as search and rescue transponder (SASR).

While some of the normal C-band FSS transponders provide wide area coverage, the other channels operate through shaped India coverage contours.

The sources said the satellite would generate about 3,700W of power from its single sided solar array configuration. The satellite's mass at lift-off would be around 2,700 kg.

Insat-3C, ISRO said, would be communication satellite providing FSS services in normal and extended C-bands, broadcast satellite service (BSS) and MSS in S-bands. The number of channels for the normal C-FSS service would be double than the usual due to the use of frequency reuse technique.

The satellite generates about 3,000 mw of power by adopting a double-sided solar array configuration. The satellite drymass would be around 1,170 kg and the lift-off mass around 2,570 kg.