Technical snag cited for the decision
THE non-building of sufficient pressure in the helium tanks in the Bahubali rocket could be the reason for calling off the moon landing mission Chandrayaan-2 an hour before its take off, say retired officials of the Indian space organisation.
If successful, India would have been the fourth country after the US, Russia and China to perform a “soft” landing on the moon.
The rocket, Geosynchronous Satellite Launch Vehicle-Mark III (GSLV-Mk III), was supposed to lift off at 2.51am on Monday with India’s second moon mission spacecraft Chandrayaan-2.
“A technical snag was observed in the launch vehicle system one hour before the launch,” the Indian Space Research Organisation (Isro) tweeted. “As a measure of abundant precaution, the #Chandrayaan2 launch has been called off… the revised launch date will be announced later.”
The retired Isro officials said there should be proper pressure in the liquid fuel tanks, so there was continuous flow of fuel to the combustion chamber.
“While the fuel is fed into the combustion chamber from the bottom, helium gas is filled from the top. It seems sufficient pressure was not being built up,” said an official. He said the flow of fuel to the combustion chamber should be uniform for the rocket to fly.
In 2006, the GSLV-F02 (different variant of GSLV) went out of control less than a minute after lift-off and had to be destroyed in the air after it started breaking up.
In its failure analysis report, an expert committee said a propellant regulator in one of the four strap-on liquid motors had a higher discharge coefficient in its closed condition.
“The reason for this could be an inadvertent error in manufacturing, which escaped the subsequent inspection, and acceptance test procedures. This regulator has functioned satisfactorily in all the previous 50 engines manufactured and tested so far,” the report said.
“The primary cause for the failure was the sudden loss of thrust in one out of the four liquid propellant strap-on stages (S4) immediately after lift-off at 0.2 seconds. With only three strap-on stages working, there was significant reduction in the control capability.
“However, the vehicle attitude could be controlled till about 50 seconds. At the same time, the vehicle reached the transonic regime of flight and the vehicle attitude errors built up to large values, resulting in aerodynamic loads exceeding the design limits thus leading to break up of the vehicle.”
The thrust of the liquid engines used in the strap-on stages was precisely controlled by a set of regulators.
“Detailed analyses have indicated that in S4 engine the thrust control was not effective. Instead of stabilising at 5.85 MPa (mega pascal) chamber pressure, it reached 7.11 MPa at 2.8 seconds. This was much beyond the design limits and the engine failed at 0.2 seconds after lift-off, that is 5 seconds after its ignition.
“The larger flow of propellant led to higher operating pressure in the gas generator (4.7 MPa against design specification of 3.6 MPa). Due to this higher operating pressure of the gas generator, the water flow rate into it got reduced. The combined effect of larger flow of propellants and reduced flow of water led to a very high gas temperature of 1.823 K against design specification of 900 K and pressure of 4.7 MPa against the design specification of 3.6 MPa.
“The very high operating pressure and temperature resulted in the structural failure of the gas generator. The consequent abrupt stopping of the turbo pumps that feed propellants at very high pressures to the engines led to loss of thrust of S4 engine.”
Isro had ruled out any sabotage theories and said the quality checks and inspections had been strengthened.
The first flight of GSLV slated for March 28, 2001, was aborted with the automatic shutdown of the main engine seconds before the lift-off. That too after the four liquid propulsion strap-on boosters started burning.
The automatic shut off system was activated when it sensed that one of the strap-on boosters did not develop the required thrust.
The rocket was flown on January 18, 2001, carrying the GSAT-1 satellite. | IANS