The launch of communications satellite GSAT-10 will be delayed by at least seven days, to September 29 from September 22, owing to a “small snag” in the Ariane 5 vehicle at the European launch pad in French Guiana.

“We will get a clear picture on the situation from [the European launch agency] Arianespace on September 19,” ISRO Chairman K. Radhakrishnan said.

GSAT-10, meant to augment the national satellite transponder capacity, carries the C- and Ku-band transponders and the second GAGAN terminal to enhance GPS indicators for local users.

Dr. Radhakrishnan said Arianespace personnel detected a small snag in the upper part of the rocket. One gram of the launcher was unaccounted for, and they were ascertaining whether dust particles of that weight had got inside.

GSAT-10 is set to fly with a European co-passenger, ASTRA-2F, on Ariane-5 ECA.

At 3,400 kg, it is the heaviest satellite the ISRO has built; but the space agency is still fine-tuning its own medium-lift rocket, the GSLV, that can put such a satellite in a geo-synchronous orbit at 36,000 km.

The indigenous cryogenic stage of the GSLV (called GSLV-MkII) had completed many tests in the past few months, and was scheduled for launch in January-February 2013, Dr. Radhakrishnan said. Labelled as GSLV-D5, it would put in orbit GSAT-14, a communications satellite. GSAT-14 would be smaller than the regular ones and would carry 12 transponders in the C- and Ku- bands.

ISRO scientists completed three reviews of the mission and were due to follow them up with a couple more. “We need to do two important tests. One is the endurance test on the fuel booster pump. The actual flight of this stage is 720 seconds. We want to take it to 1,000 seconds. The second one is to ignite the cryogenic stage at a high altitude in vacuum condition. In the next two months, we plan a vacuum test at Mahendragiri [in Tamil Nadu].”

The four-tonne satellite lifter, GSLV-MkIII, under development, would be flown by September next year.