CHENNAI: Isro is planning three launches in May including GSLV MK-II carrying the South Asia Satellite and the first developmental flight of GSLV MK-III, capable of lifting a 4-tonne payload, said P V Venkitakrishnan , director, Isro Propulsion Complex on Tuesday.Speaking on the sidelines of the 58th Institute Day of IIT Madras, Venkitakrishnan said there would be at least a 25-day gap between GSLV MK-II, scheduled to be launched early in the month, and GSLV MK-III planned for the end of May. The time between the two launches will enable scientists to refurbish the stages, as both the rockets will take off from the same launch pad. Isro chairman Kiran Kumar had earlier said GSLV MK-II would be launched on May 5.PSLV C38 is also planned for next month, but the launch will happen depending on the priority and availability of the satellites, Venkitakrishnan said. "The vehicles are ready," he added.Expressing confidence over the success of the first developmental flight of GSLV MK-III powered by an indigenous cryogenic upper stage , Venkitakrishnan said they would have two more developmental flights to optimise its payload capacity before reaching the operational phase."When we did the first stage test for 50 seconds on the cryogenic upper stage for MK-III, we did not face any problem. We did it right in the first go and I don't think there will be any problem in the first flight," he said.