Possible reasons for Vikram's landing failure: Here's what the experts say

Vikas SV

New Delhi, Sep 19: India's ambitious Chandrayaan-2 suffered a setback on September 7 when the mission's moon lander Vikram lost contact from ISRO's ground station. Vikram was on its descent to soft land on the Moon's south polar region when the communication links snapped.

The Chandrayaan-2's orbiter has since spotted the lander on the surface of the Moon, and it is said to be unbroken, but tilted on its side. Things were initially looking good for the Vikram lander, the rough braking and the fine braking phases of the descent were smooth and went as planned, but then, 2.1 kms above lunar surface, something happened. For sure, the final descent was far more rapid than what should have been, but stilll it was not exactly a 'crash land' which left the lander smashed.

The Vikaram lander's structure is intact, but is in tilted position. ISRO is yet to give official reason for landing failure.

Vikram's landing failure: Here's what has appeared in the media thus far:-

Some are pinning blame on the central engine which was supposed to have taken over lander's descent from smaller engines during the final phase. The balance between the speed of fall due to moon's gravitational pull and upward thurst could not be maintained and Vikram thudded on the surface.

An IANS reports quoted an ISRO official as saying that the lander could have lost its control when its thrusters were switched off during its descent, and crash-landed snapping the communication links.

At an altitude of about 5 km from the lunar surface, the lander slightly veered off its plotted path before returning to its original path immediately, the report further said.

The BBC quoted Prof Roddam Narasimha, a former member of Isro, as saying the problem could well have been with the lander's central engine. He believes this could be because the central engine was not "producing the thrust that is required and, therefore, the deceleration was no longer what it was supposed to be".

[Long shadows block clear view as NASA fails to spot silent Chandrayaan 2 Vikram Lander]

Mylswamy Annadurai, told BBC that the anomaly in the velocity profile was an indication that something had malfunctioned in the lander as it hurtled towards the Moon.

"Most likely the orientation [of the lander] could have been disrupted. Once we look at the data we will be able to say for sure what happened, but it is likely that either a sensor or a thruster could have malfunctioned," he told BBC.

"Just before the loss of communication link, the lander tumbled but recovered immediately. After that the communication signals snapped. That means the lander in its trajectory lost its position," an ISRO official told IANS on the condition of anonymity.

Landers could kick up a cloud of dust that blocks sensors from detecting the craters or boulders that a last-minute engine burn might avoid. And the thrust could displace enough lunar matter that the spacecraft lands tilted, a position that could prevent a rover from rolling out safely.

All was going well with the 1,471 kg Vikram that had begun its descent at about 1.38 a.m. on Saturday from an altitude of 30 km at a velocity of 1,680 metres per second.

Chandrayaan 2's lander, Vikram, had to slow down to near to successfully soft land on the Moon's surface. The speed went down from 1.6 km per second at the start of the vertical descent to 48.59 metres per sec when the signal was lost, a report published in www.businessinsider.in said.

[Last day today for ISRO to establish communication with Vikram Lander]

ISRO has released few details about effort to locate and restore contact with the lander. A Sept. 10 statement, the most recent one from ISRO, said that the Chandrayaan-2 orbiter had taken an image of the lander, but said nothing about the state of the lander beyond the continued lack of communications. ISRO also hasn't released the image.

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