Chandrayaan 2: Why landing went belly-up

Bengaluru: India’s first lunar lander ‘Vikram’ veered away from the designated path and tumbled before snapping the communication link with ground stations because of a sudden burst in speed during its descent owing to a malfunctioning system, say Indian space scientists.

Minutes before loss of communication, ‘Vikram’ digressed from its path because of acceleration instead of deceleration owing to a malfunctioning mini rocket engine or the effect of scorching heat on the gyro and accelerometer.

Four thrusters were fitted on board the lander to support the descent operation, and decrease the speed from 1.6 km a second to almost zilch, and were programmed to function in sync with one another. Perhaps, one of them malfunctioned, resulting in loss of trajectory, scientists added.

The lander performed to perfection during the first two of four phases-rough breaking phase, fine breaking phase, hovering phase and parabolic descent-prompting space scientists to break into applause as the speed during descent decreased from 1.6 km a second to 60 meters a second. It, however, started swerve when at a distance of about 5 km from the landing spot. This was noticed on the telemetry screen at ISTRAC, Bengaluru, but as it was on automated descent, no action could be initiated from ground stations.

Scientists also pointed out that the communication link snapped as the lander collided with a large mound after deviating from its path.

They did not rule out a combination of factors-malfunctioning thrusters, gyro and accelerometer-for the setback. The gyro and accelerometer, perhaps, were affected by soaring temperature of the spacecraft during the glide.

On Saturday morning, Dr K Sivan, Chairman, ISRO, couple of his predecessors, and members of Team Chandrayaan-2 pored over data from all systems for more than five hours but could not arrive at a conclusion on the cause for lander's failure. Though Dr Sivan and others took a break from the probe, others continued to sift through data to find out the rogue component which caused the setback, scientists added.