Chennai, April 25 - With 5.47 a.m. Thursday set for the blast-off of the Indian rocket carrying a remote sensing/earth observation satellite - Radar Imaging Satellite (Risat-1) - into space, the Indian space agency is fuelling the rocket's second stage with liquid propellant.

"The major activity today (Wednesday) is the filling up of the liquid fuel in the rocket's second stage. The countdown is progressing well and every system in the rocket is normal," a source in the Indian Space Research Organisation (ISRO) told IANS.

The indigenous Risat-1 with a life span of five years would be used for disaster prediction and agriculture forestry, and the high resolution pictures and microwave imaging could also be used for defence purposes.

The rocket is ready to escape the Earth's gravity to put India's heaviest microwave satellite, Risat-1, weighing 1,858 kg at an altitude of 480 km at an inclination of 97.552 degree.

The rocket that would sling Risat-1 will be the four-stage Polar Satellite Launch Vehicle's (PSLV) upgraded variant called PSLV-XL which would weigh 320 tonnes at lift-off.

Space scientists do not expect any problem with the PSLV's performance though it would be carrying its heaviest luggage so far.

"Depending on the satellite's weight, the rocket's centre of gravity would change. Slight changes will have to be made in the navigational parametres. The control systems would have to be tuned accordingly," an ISRO source said.

While satellite weight is a major criteria, the other metric is the altitude at which the rocket would sling its luggage.

Satellite mass to altitude is also related. The rocket would sling the satellite at 480 km Thursday and as such officials do not see any hitch in the mission ending successfully.

The PSLV's four stages are fuelled with solid and liquid propellants. The first and third stages have solid fuel while the second and fourth stages are powered by liquid fuel.

The PSLV rocket has earlier put satellites at altitudes ranging between 630 km to 820 km.

"Lower the weight of the satellite, PSLV can spit out the satellite at higher altitude and vice versa is also true," the ISRO source said.

According to ISRO officials, the rocket launch will be controlled by space scientists at the new mission control centre inaugurated by President Pratibha Patil this January.