Bengaluru: Ever since the Indian Space Research Organization (ISRO) announced the launch of Chandrayaan-2, its most ambitious mission till date, it had put just one caveat -- the crucial powered descent on the moon, which it was attempting for the first time.

India had been to the moon before with the successful launch of Chandrayaan-1 in 2008, which gave the world evidence of water molecules on the lunar surface. So, it was evident that the team was confident of accomplishing the feat again.

The crucial manoeuvres required to place a spacecraft into the desired moon orbit , the trans-lunar injection and lunar orbit insertion had gone precisely as planned for Chandrayaan-2. The inclination to the lunar surface was closer to precision. Lander Vikram had successfully separated from Orbiter and de-orbited to an elliptical orbit of 35 X 100 kms, from where it began the powered descent on Saturday.

But it was during the last phase of the mission which involved executing a soft landing on the moon - new to ISRO, that the results did not go as planned. In the days leading to the final event, ISRO chairman K Sivan had described the moments as "15 minutes of terror" when Lander Vikram would entirely be on its own, with no ground control to guide it.

On Saturday, during those 15 minutes the enthusiasm of the entire team turned into despair. Lander Vikram lost all communication with the ground station during the last two minutes when it was just 2.1 km above the lunar surface.

The power descent was indeed one of the most complex exercises that ISRO had ever undertaken, which involved reducing the velocity of the Lander from 1.6 km/second to zero in a controlled manner. The agency made use of a new technology-- the five thrusters which would be fired in stages to bring down its velocity.

All simulations, testing and verification were done several times on earth. But there were uncertainties involved in executing it on the moon. The moon has no atmosphere and the gravity is one-sixth of that of earth, and actions have to be performed accordingly. There was no muscle memory of landing on the moon.

A similar attempt by Israel in April could not achieve success. But, ISRO tried to learn from that and decided to strengthen the sensor characterisation of Lander so it does not get impacted due to any human error. It also accounted for any communication delay, because the Lander was designed to be autonomous and take decisions on its own.

But, it could not control the velocity during the last two minutes and could not achieve a soft landing on the moon. The orbiter, however, continues to revolve around the moon at an altitude of 100 km above the surface and would continue the Chandrayaan-2's exploration.


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