Top ISRO officials are studying the Polar Satellite Launch Vehicle’s (PSLV) flight data to understand why the rocket’s heat shield did not separate during the August 31 launch, that caused the failure of the Rs 250-crore mission.

“We are studying the data. We cannot say now why the rocket’s heat shield did not separate as planned,” K. Sivan, Director, Vikram Sarabhai Space Centre (VSSC) said.

The VSSC is part of the Indian Space Research Organisation.

According to Sivan, the pyro elements in the rocket which enable separation of the heat shield have to be probed.

The exact cause of the mission’s failure can only be determined once the officials conclude their study.

“Based on the data, simulation experiments have to be carried out to arrive at the probable cause of the failure,” Siwan added.

On August 31, the heat shield of PSLV’s XL variant did not separate three minutes after crossing the atmosphere.

As a result, India’s navigation satellite IRNSS-1H was trapped and not put into orbit.

Satellites are housed atop the rocket and covered by a heat shield or payload fairing, which protects them from getting burnt when the rocket crosses the atmosphere at maximum speed.

Speaking to IANS, M.Y.S. Prasad, former director of Satish Dhawan Space Centre, said: “The computers have to be given the necessary commands which are then relayed by the electrical circuits. The pyro circuit has to get initiated, which in turn has to cut the mechanical elements so that the two parts of the heat shield get separated.”

Prasad said anything could have gone wrong in the four-step sequence and sub-systems.

“The computer programmes may have several redundancies to take care of an eventuality. So, they can be tested on the ground before and also during preparation for the flight. The electrical circuits and some pyro elements will also have redundancy,” he said.

“A rocket has several one-time operation systems. Such systems cannot be pre-tested and cannot have redundancies. Only sample tests can be made with items manufactured in that batch. And then a system is used in the rocket,” he added.

“The one-time operation system is the riskiest items for any rocket.”

Ruling out a failure in design, Prasad said the most probable cause of the failure could be the quality of a rocket component or some error in the assembly.

The 1,425-kg IRNSS-1H satellite was supposed to be a replacement for IRNSS-1A satellite.

The IRNSS stands for Indian Regional Navigation Satellite System and has been renamed as NavIC (Navigation with Indian Constellation).

The IRNSS or NavIC is similar to the US-owned GPS.

The IRNSS-1H became a necessity as the rubidium atomic clocks of IRNSS-1A have failed. The atomic clocks are important to provide the accurate positional data.

The Rs 1,420-crore Indian satellite navigation system NavIC consists of nine satellites — seven in orbit and two as substitutes. One of the substitutes was the IRNSS-1H.

ISRO officials said that the other standby satellite has to be ready for launch.