Delay in wing deployment caused Nirbhay missile’s third failure

By By Anantha Krishnan M

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The malfunctioning of the mechanism that deploys the wing appears to have resulted in the subsonic cruise missile Nirbhay developing a very high roll-rate, which led to the Inertial Navigation System (INS) losing its frame of reference. Read the exclusive report by our Defence Correspondent

Bengaluru: The recent failed mission of subsonic cruise missile Nirbhay is pointing towards a slight ‘pause’ (delay) during the process of wing deployment. This malfunctioning of the mechanism that deploys the wing appears to have resulted in the missile developing a very high roll-rate, which led to the Inertial Navigation System (INS) losing its frame of reference. This caused the missile to veer away from its intended flight path, leading to a situation which called for aborting the mission from safety considerations.

Sources within the Defence Research and Development Organisation (DRDO), who reviewed the video footage of the missile’s failed flight, confirmed to Mathrubhumi that the wing is normally deployed in less than 500 milli-seconds (0.5 sec.) after booster burn-out and separation of the booster section from the main missile.

“In the previous missions, we have been achieving the wing deployment in around 300-350 milli-seconds. This time the wing seems to have got stuck at 60 degrees position for about 1.5 seconds causing the damage. This is what we have assessed so far. The missile appears to have developed the high roll rate due to the partially deployed wing”, an official said.

During the vertical launch of the missile the booster fires for about 10 seconds, resulting in the missile gaining height and acceleration. It is in this phase that the Thrust Vector Control (TVC) system rotates the missile from vertical to horizontal attitude. On burn-out of the booster, the booster section is detached from the main missile by activation of pyro-bolts. Small thrusters ensure that the detached section separates safely from the main missile.

The Onboard Computer (OBC), which manages all these critical events, initiates the wing deployment process after separation of the booster section. After wing deployment, the cruise phase engine is started, which takes about six seconds to develop the operational speed (RPM) and thrust required to sustain the flight of the missile.

“At this point the control system puts the missile through a constant altitude phase for a short duration before initiating the pre-programmed way-point navigation phase of the mission,” says the official.

One perfect mission and three misses so far

During the first launch of Nirbhay, the output from one of the sensors of the INS froze for a short duration. Though a redundant sensor was available, the navigation system lost its reference and the missile deviated from its intended flight path. After about 15 minutes of flight from ‘range safety considerations,’ the mission had to be aborted by destroying the missile.

The second launch of the missile was a success and the missile travelled for about 72 minutes covering around 1050 km, meeting all mission objectives.

The third mission again failed owing to a malfunction of the control system. Incidentally, it is understood from reliable sources that the particular system had indicated a problem during the pre-launch checks, during the countdown. The launch was delayed by a few hours, and the system was cleared when it was seen to be working after some investigation.

“The missile went through the launch phase, but the control system failed during the flight. This probably points to avoidable haste in clearing the system and inadequate implementation of quality standards and procedures,” says the official. He said the DRDO is working on a digital controller for the actuator to replace the control box which caused the failure.

During the fourth recent flight, the wing appears to have rubbed against a supporting bush and was held in that position for a short duration of time, which caused a pause in the deployment process. “The video from the 4th flight and the telemetry data clearly show the pause,” says the official.

Sources say there could be flaws in the details of design implementation. With most of the components being ‘fabricated’ in small numbers, rather than being ‘manufactured’ in larger quantities, there are quality concerns as well.

“The chaltha-hain attitude of those at the assembly lines after some initial success, is also a cause of worry,” says the official.

ADE has no rift with Missile Complex team

When asked about the widely-talked about rift between Team Nirbhay at Aeronautical Development Establishment (ADE) and those linked to the project from the Missile Complex at Hyderabad, the official said: “We haven’t faced such issues. There could be a difference of perspective which cannot be termed as rift. This is a project sanctioned to the Aero cluster and the Missile Complex has always extended whole-hearted support.”

For Nirbhay, the booster comes from ASL (Hyderabad); while the thrust vector control system and INS is from RCI (Hyderabad) and the launcher from R&D Engineers (Pune). The booster is designed by ASL (Hyderabad); the propellant comes from HEMRL (Pune) and the power plant is from a foreign source. The missile’s total system design and integration is done at ADE, Bengaluru.

DRDO’s DG (Aero) C P Ramanarayanan did not respond to repeated calls on his mobile for an official version. He is said to have been pulled by the Defence Minister and the PMO soon after details of the failed mission was out in the media.

Despite three failures in four missions, the Ministry of Defence is understood to have extended the PDC (Probable Date of Completion) by another one-and-a-half years (till mid of 2018). In the last 12 years, around Rs 120 crore has been spent on this project.

Insiders in ADE say that inadequate PDCs are killing the project. “More time and money should be given for this project. Repeated extension of the project with incremental PDCs makes it impossible for the team to effectively process procurements and outsourced developments within available time-frame. Whenever procurement is cleared, if the delivery of the item is not within the PDC, then it is not processed. This slows down the project further,” says a scientist.

(The writer tweets @writetake.)

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