The GSLV-D3 launch was primarily for the flight testing of the indigenously developed Cryogenic Upper Stage (CUS). The third developmental flight of India's heaviest rocket ended in the Bay of Bengal soon after its lift-off as the cryogenic engine failed to perform as expected.
The Indian Space Research Organisation (ISRO) had set up an expert committee to go into the probable cause of failure and recommend corrective measures.
Studying in detail the launch sequence, the committee has said: "The initial conditions required for the start of the indigenous cryogenic upper stage (CUS) were attained as expected and the CUS start sequence got initiated as planned at 294.06 seconds from lift-off."
According to committee report, the ignition of the CUS main engine and two steering engines have been confirmed as normal, as observed from the vehicle acceleration and different parameters of CUS measured during the flight.
"Vehicle acceleration was comparable with that of earlier GSLV flights up to 2.2 seconds from start of CUS. However, the thrust build up did not progress as expected due to non-availability of liquid hydrogen supply to the thrust chamber of the main engine," the committee reported.
The committee attributes the fuel supply failure to the stopping of fuel booster turbo pump.The committee said the start-up of fuel booster turbo pump was normal. It reached a maximum speed of 34,800 rpm and continued to function as predicted after the start of CUS.
However, the speed of turbo pump started dipping after 0.9 seconds and it stopped within the next 0.6 seconds probably due to the gripping at one of the seal location and seizure of rotor, or the rupture of turbine casing, caused probably due to excessive pressure rise and thermal stresses, the report said.
After incorporating necessary corrective measures, the flight testing of the Indian-made cryogenic engine in GSLV is targeted within a year. In the meantime, the next two GSLVs would fly with the available Russian-made cryogenic engines, the committee said.
