Chandrayaan-3’s lander, which is expected to leg down on the moon this evening, will ‘free-fall’ on the lunar surface during the last 10 metres of its descent. 

The lander, which is circling the moon right now, will begin its downward journey at a height of 30 metres, this evening around 5:30 pm, IST. It will then move on a curved path, losing altitude and speed. 

There are three distinct phases in the lander’s descent.  

In the first, ‘rough braking’ phase, the lander will slow down a lot, using the four thrusters (engines) onboard, which will push the lander in a direction opposite to its motion. 

Then, in the camera coasting phase, the camera on board will ‘look at’ where the lander is headed to and match the sight with the landing area given to it previously. Incidentally, the landing area has been enlarged this time – from 0.5km x 0.5km for Chandrayaan-2, to 2.4 km x 4 km for Chandrayaan-3. 

After the camera coasting phase, the lander will move into the ‘fine braking’ phase, when the vehicle will slow down further and assume a vertical position so as to land on its legs. 

Dr P V Venkitakrishnan, a former ISRO rocket scientist who now teaches at IIT Madras, told businessline today that the legs of the lander have been strengthened. The vehicle itself has been given an extra mass of 100 kg for better stability.  

Answering a question, Venkitakrishnan said that the lander of Chandrayaan-2 had a central thruster, which has been removed this time, as it was not contributing much. Also, if the vehicle tumbles, or rolls over, it can do so faster than last time (25 degrees per second compared with 10 degrees a second last time), so that it can come back to its position faster. However, “tumbling will not happen this time,” he said. 

Nor is the lander likely to lose communication—as did Luna 25 of the Russians a few days ago, he said. This is because of redundancies built in the orbiter of Chandrayaan-2, which is still in service and is orbiting the moon, is available as a back-up for communication.  

Therefore, all possible pain-points have been addressed, but one will have to keep his fingers crossed till the soft-landing happens. If it does, India will not only be the fourth country in the world to achieve a lunar soft-landing (after the US, Russia, and China) but also the first in the world to soft-land in the South-polar region of the moon. 

Prof Satya Chakravarthy, an aerospace expert at IIT Madras, says: “Chandrayaan-3’s chances of success have been maximised by ISRO. Its successful landing is globally significant for three reasons. First, India will be the first one to land on the lunar South Pole. Second, India’s frugality with its space program will again be a talking point around the world’s capitals. Finally, it will inevitably be contrasted with the ill-fated Luna-25 to point out the emergence of a new world order among space-faring nations. ISRO is definitely pushing the chances of India being increasingly viewed as an advanced country fast.” 

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