Chennai: A faulty propellant regulator in the first stage of the three-stage Geosynchronous Satellite Launch Vehicle (GSLV) F02 has been identified as the cause of the blowing up of the rocket launcher on July 10, 2006 mid air
After studying the flight data and verification through calibration tests the 15-member Failure Analysis Committee (FAC) under the chairmanship of K Narayana, former director, Satish Dhawan Space Centre, Sriharikota has arrived at its decision.
However, what is surprising is the committee giving a clean chit to the component manufacturer and also to the others involved in checking the component quality when it says, "The reason could be an inadvertent error in manufacturing, which escaped the subsequent inspection and acceptance test procedures." In a way the committee ruled out sabotage as well.
GSLV-F02 launch was the fourth in the series. All the three earlier missions (GSLV-D1, D2 and F01) were completely successful. The mission objective of GSLV-F02 was to place INSAT-4C, an operational satellite into geosynchronous transfer orbit (GTO). About 55 seconds into the flight, GSLV-F02 started deviating significantly from its flight path.
FAC had detailed deliberations for over 100 hours in several sittings and was assisted by eight specialist sub-committees examining the flight data of vehicle subsystems, manufacturing documents, inspection, calibration and test results, etc. Especially, the details related to the realisation of liquid propulsion stage of GSLV were closely scrutinised. Several tests simulating possible failure modes were also conducted to identify the exact cause.
FAC has concluded that the performance of all vehicle subsystems, except one strap-on stage was normal until 56.4 seconds. 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.
The thrust of the liquid engines used in the strap-on stages is 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 sec. 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.
FAC has concluded that the design of GSLV is robust and recommended implementation of strict control on fabrication, inspection and acceptance procedures. Among others, FAC has recommended fabrication processes to be critically reviewed and updated. It has recommended for independent inspection of all critical dimensions of components and subassemblies by in-house agencies. Further, long duration hot test on one out of every 20 engines fabricated has been recommended to ensure that production process is under control. In addition, FAC has recommended strengthening the process of clearance of launch during Automatic Launch Sequence (ALS) phase.
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GSLV in mid air