The Indian Space Research Organisation (ISRO) is postponing its first scheduled commercial launch of 2010 after discovering a fault in the rocket’s second stage, ISRO announced April 29.

The Algerian communications satellite ALSAT-2 and two nanosatellites from Canada’s University of Toronto were scheduled to launch May 9 atop a Polar Satellite Launch Vehicle (PSLV), but will have to wait until ISRO scientists address an unexpected pressure drop that occurred during prelaunch tests at the Satish Dhawan Space Centre in southern India.

The four-stage PSLV uses liquid propellant in the second and fourth stages and solid fuel in the first and third stages. ISRO, in a short statement, said that “a marginal drop in the pressure in [the] second stage of the vehicle was noticed during the mandatory checks carried out” in preparation for the launch and that the new launch date “will be decided after preliminary results of the analysis are obtained.”

ISRO sources speaking on condition of anonymity said it was too soon to set a new date for the launch since the fully assembled rocket has to be dismantled to remove the second stage before engineers can identify and correct the fault. These sources said it may be necessary to return the rocket to the Vikram Sarabhai Space Centre in Thiruvananthapuram, where the rocket was built.

According to sources, though the pressure drop detected during the test was minor, ISRO decided to postpone the launch rather than risk another failure. On April 15 ISRO’s Geosynchronous Satellite Launch Vehicle plunged into the sea due to a failure of its new, domestic cryogenic upper-stage engine.

In addition to the foreign satellites, the postponed PSLV launch was expected to put in orbit India’s own cartography satellite Cartosat-2B and a microsatellite made by Indian students.