Chennai: The countdown for Monday's launch of India's Polar Satellite Launch Vehicle (PSLV) rocket carrying five satellites, including a cartography one for land mapping and information, began on Saturday at the rocket port Sriharikota.

The 44-metre tall PSLV is a four-stage rocket powered by solid and liquid propellants alternatively.

"Everything is going smoothly and we are getting ready for the Monday launch. The 50 hours, 30 minutes countdown started at 6.52 a.m. on Saturday," S. Satish, director at the Indian Space Research Organization (ISRO), told the sources from Bangalore.

The rocket will blast off into space from Sriharikota, around 80 km from here, carrying the 694 kg Cartosat 2B and an Algerian satellite, Alsat (117 kg).

It will also carry three very small satellites - NLS 6.1 and NLS 6.2 from Canada and Switzerland, and StudSat - developed by students of engineering colleges in Bangalore and Hyderabad.

"The satellites were loaded atop the rocket a couple of days ago," an ISRO official said.

The first and third stages of the rocket are fired by solid propellant and the second and fourth stages are fired by liquid propellant.

According to ISRO officials, the solid fuel stages are cast ready while the liquid fuel - Unsymmetrical Di-Methyl Hydrazine (UDMH) as fuel and Nitrogen tetroxide (N2O4) as oxidiser - will be filled hours before the blast off.

The rocket's main cargo Cartosat-2B is a remote sensing satellite carrying a sophisticated panchromatic camera on board to photograph specific spots closely. The pictures are useful for cartographic applications such as mapping, land information and geographical information system.

Cartosat- 2B will join the other two cartography satellites Cartosat- 2 and 2A launched earlier. With three satellites ISRO's satellites can cover the country effectively.

ISRO has been carrying out multiple launches for several years. In 2008 it set a world record launching 10 satellites at one go.

Originally scheduled for launch on May 9, ISRO decided to postpone the launch as it found "a marginal drop in the pressure in the second stage of the vehicle during mandatory checks" due to a faulty valve.

At that time the rocket was almost ready except for the loading of the satellites.

As the faulty valve was in an inaccessible area with the rocket stages having been fully assembled, the second stage had to be dismantled to take corrective action.

Even after the replacement of the faulty valve at Sriharikota the problem continued to persist and ISRO sent the second stage (engine and other systems) back to its assembly centre.

"The second stage was refurbished and sent back to Sriharikota," Satish said. IANS