By Venkatachari Jagannathan

Chennai, Apr 30 (IANS): The Indian space agency is likely to launch its rocket, Polar Satellite Launch Vehicle (PSLV-C15), carrying its cartography satellite Cartosat-2B and couple of other payloads, sometime in June.

Originally scheduled for launch May 9, the Indian Space Research Organisation (ISRO) Thursday decided to postpone the flight to a future date as it found "a marginal drop in the pressure in the second stage of the vehicle during mandatory checks".

A source in ISRO told IANS: "The faulty part is in an inaccessible area as the rocket stages have been fully assembled. The second stage has to be dismantled to spot and correct the fault."

According to the source, the rocket is almost ready except for the loading of the satellites that have arrived at the launch centre in Sriharikota, around 80 km from here.

"The leak was not found during the earlier tests before the stages were integrated," the source told IANS.

The dismantling will be done from the top which involves - removal of the electronics assembly, fourth and third stages - so as take away the second stage.

The fault will be rectified at Sriharikota launch centre or if need be taken to ISRO's centre in Trivandrum which, the official said, is a remote possibility.

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

The first and third stages 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 - measuring around 41 tonne, will be filled hours before the blast off.

Testing of the stage sub-systems will be done with nitrogen and helium gas, explained an ISRO official.

"With the help of these gases, we will test the integrity of the stage. Compared to the solid stage the liquid stage has more intricacies. It has various sub-systems, valves, turbines, regulators and other complex systems which have to be tested on ground."

Though the pressure drop was marginal, ISRO decided to postpone the flight of its successful rocket as it does not want to risk another failure in quick succession.

It may be recalled that ISRO's heavier rocket Geosynchronous Satellite Launch Vehicle (GSLV) went down into the sea April 15 as its own cryogenic engine was not able to sustain combustion beyond one second as one of its turbo pumps was not able to function continuously.

Further, PSLV has been the revenue earner for ISRO, launching third party satellites and a failure would have a reputation issue which in turn would impact a lucrative revenue stream.

PSLV this time is slated to ferry an Algerian Alsat communication satellite weighing 117 kg for a fee. The rocket will also carry two nano satellites - one each from Canada and Switzerland - a pico satellite StudSat (under one kg) developed by college students in Bangalore and Hyderabad.

However, the main cargo of the rocket is the Cartosat-2B 690-kg satellite, which will carry a sophisticated panchromatic camera on board to take higher (0.8 metre) spatial resolution imageries with a swath of 9.6 km of specific spots for cartographic applications such as mapping, land information and geographical information system.