What is a 'soft landing'? Why is it crucial for the Chandrayaan-3 mission?

ISRO is gearing up for the launch of the Chandrayaan-3 mission, which seeks to succeed where its predecessor failed—to achieve a 'soft landing' on the lunar surface.

Scheduled for launch on July 14, the mission, if successful, would be yet another milestone for India, which has emerged as potent space power over the past couple of decades.

With excitement building up for the launch, we examine what a 'soft landing' is in aeronautics parlance, and why it's so important for the mission.

What is a 'soft landing'?

Simply put, a 'soft landing' refers to the successful landing of a spacecraft without it suffering any significant damage to either itself or its payload.

In contrast, a 'hard landing', while distinct from a crash, often results in considerable damage to the landing vehicle, which, in the context of space missions, may render the mission untenable owing to damage to scientific instruments and/or equipment.

To put things into perspective, the Chandrayaan-2 mission had aimed to achieve a 'soft landing' on the lunar surface.

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However, the mission, or at least a large part of it failed, when the Vikram lander encountered a software glitch, thereby resulting in a "hard landing", in the words of then ISRO chief K Sivan.

While the Chandrayaan-2 orbiter is still intact and in lunar orbit, the hard landing of the Vikram lander essentially rendered moot the rest of the mission, which had intended to study the lunar topography using a robotic rover.

Why is a soft landing important for Chandrayaan-3?

Chandrayaan-3, unlike its predecessor, does not have an orbiter module. It's sole purpose is to do what Chandrayaan-2 could not, namely, to land on the lunar south pole and explore its topography using a rover.

Any damage sustained during landing is likely to affect the rover, and could seriously jeopardise the mission.

Given this possibility, and given the experience with Chandrayaan-2, ISRO has been particularly careful this time around.

Taking lessons from the malfunction of the Vikram lander, ISRO has opted for a "failure-based design" that takes into account the various possible points of failure.

To that end, ISRO has accounted for possible malfunctions in sensors and engines, and has also accounted for possible issues with algorithms or calculations.

Further, the designated landing area has been increased by four times in comparison to Chandrayaan-2 to allow for a greater margin of error if conditions change on the fly.

ISRO hopes these considerations will allow it to carry out a soft landing successfully, a feat that would take India into an elite club comprising the United States, China, and the former Soviet Union.