Sriharikota (Andhra Pradesh), Aug 19 (IANS): Delaying India's entry into a select group of nations with cryogenic engine technology, the Indian space agency Monday had to call off the launch of its heavy rocket, the geosynchronous satellite launch vehicle (GSLV-D5), after a fuel leak was detected.

Indian Space Research Organisation (ISRO) chairman K. Radhakrishnan said: "The countdown for the rocket launch was progressing well. (But) Two hours before the scheduled launch time, we observed a leak in the fuel system of the second-stage engine."

"Because of that, we are calling off the launch. The liquid fuel in the second stage and the four strap-on motors of the first stage and the cryogenic engine will be drained," he told media at the Satish Dhawan Space Centre here.

According to him, the rocket, which cost Rs.160 crore, will then be moved to the rocket assembly building to make an assessment of the leak's cause and the action that needs to be taken. The GSAT-4 communication satellite it was was to carry into space costs Rs.45 crore.

He said the revised launch date will be announced after the leak assessment.

Nearly two hours before the scheduled blast off (4.50 p.m.) while the cryogenic engine - developed by Indian space scientists after around two decades of labour at an outlay of around Rs.400 crore - was being fuelled up, scientists and officials at the mission control centre got suddenly excited and huddled in a serious discussion.

Small groups of scientists gathered around some monitors. The countdown was put on hold for some time and an emergency meeting was called where a decision was taken to hold the launch.

The fuel leak was also visible on the television screen at the launch centre.

The GSLV's success-failure ratio is skewed towards the latter. Out of the seven GSLV rockets that soared into the skies till date, four have turned out to be failures for ISRO.

While two missions were successful, one is considered as partial success as the rocket under-performed.

The two successful launches were in 2003 and 2004 when the rocket launched GSAT-2 and Edusat, an educational satellite.

The rocket's maiden flight in 2001 was a failure as it was not able to sling GSAT-1 into its intended orbit.

The 2006 mission was sort of an historic flight for a dubious reason. For the first time, ISRO destroyed the rocket mid-air soon after the take-off as it started backing up.

The 2007 flight is considered as a partial success. At that time, 15 seconds before the lift-off, the rocket's computers -- which takeover checking of the systems 12 minutes before lift-off -- put GSLV on hold after detecting anomalies in the cryogenic fuel stage.

The launch was postponed by two hours to set right the problem even as ISRO officials were considering rescheduling the launch by another two days.

However, the detection of one of the vent valves in the cryogenic engine that had not shut properly led to its immediate rectification.

ISRO scientists were on tenterhooks till the last moment as for a few seconds during the final cryogenic stage signals from the rocket failed to reach the ground stations.

After a three-year gap, ISRO flew a GSLV in April 2010 with its own cryogenic engine. The mission failed due to the problem in the cryogenic engine's fuel booster turbo pump.

Another GSLV went down in December 2010 after it veered off its designated path and exploded mid-air. For the second time, a GSLV rocket was destroyed mid-air for safety.