Non-availability of liquid hydrogen reason for GSLV-D3 failure

Non-availability of liquid hydrogen supply to the thrust chamber of the main engine could have resulted in failure of the third developmental flight of Geosynchronous Satellite Launch Vehicle (GSLV) from Sriharikota on April 15, a failure analysis committee has found.

The flight of GSLV-D3, primarily meant for testing of indigenously developed cryogenic upper stage (CUS), had failed to achieve the mission objectives following which ISRO had instituted a two-tier process to carry out an in-depth analysis of the flight performance and identify the causes of the failure and recommend corrective measures.

As per review of the findings by the National Group of Eminent Experts, though the ignition of the CUS main engine and two steering engines were confirmed normal, the thrust build up did not progress as expected "due to non-availability of liquid hydrogen (LH2) suppy to the thrust chamber of the main engine", an ISRO release said.

The failure is attributed to the anomalous stopping of fuel booster turbo pump (FBTP). "The start-up of FBTP 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 FBTP started dipping after 0.9 seconds and it stopped within the next 0.6 seconds," it said.

Two plausible scenarios have been identified for failure of FBTP, gripping at one of the seal locations and seizure of rotor and a rupture of turbine casing caused probably due to excessive pressure rise and thermal stresses, it said.

As per the review, following a smooth countdown, the lift-off took place at 1627 hours (IST) as planned. All four liquid strap-on stages (L40), solid core stage (S139) and liquid second stage (GS2) functioned normally, it said. The vehicle's performance was normal up to the burn-out of GS-2, that is, 293 seconds from lift-off, the release said.

Altitude, velocity, flight path angle and acceleration profile closely followed the pre-flight predictions. All onboard real time decision-based events were as expected and as per pre-flight simulations, it said.

The navigation, guidance and control systems using indigenous onboard computer Vikram 1601 as well as the advanced telemetry system functioned flawlessly, it said.

The composite payload fairing of 4m diameter inducted first time in this flight, also performed as expected. Performance of all other systems like engine gimbal control systems and stage auxiliary systems was normal, it said

The initial conditions required for start of the indigenous CUS were attained as expected and the CUS start sequence got initiated as planned at 294.06 seconds from lift-off, the release said.

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, it said.

However, the thrust build up did not progress as expected due to non-availability of liquid hydrogen (LH2) supply to the thrust chamber of the main engine, it said.

Following the review, "a series of confirmatory ground tests are planned", the release said

After incorporating necessary corrective measures, the flight testing of indigenous cryogenic upper stage on GSLV is targeted within a year, it said.

In the meantime, the next two GSLVs would fly with the available Russian cryogenic stages, it said.