The 15-minute power descent to be most challenging
India is executing a soft landing for the first time. The success rate of soft landings on the Moon has so far been just 37%
New Delhi: Early on Saturday, when Chandrayaan-2’s lander Vikram would be the closest to the Moon, about 35 km above the lunar surface, it will begin its most challenging manoeuvre till date—the 15-minute power descent.
As it comes down, it will hover over the rugged lunar surface, continuously scanning for the targeted site near the south pole of the Moon as loaded on board by the Indian Space Research Organisation (Isro) until it’s sure that it has found the designated site for landing.
To overcome the communication delay, scientists have ensured that there is no ground control from earth during the 15-minute exercise, which begins at 1.40 am on Saturday. All decisions about when and where to land would be autonomously taken by the lander.
“Enough simulations and testing have been done, but there is still a lot of uncertainty involved. Even if there is a small miscalculation in sensor characterization, the whole exercise gets jeopardized. Even if there is a small rock or boulder on the landing site, it could topple it," said Patrick Dasgupta, a professor at the department of physics and astrophysics, University of Delhi.
The lander will have to reduce its velocity from 1.6km per second to zero in 15 minutes for a controlled soft landing.
India’s space agency is for the first time using five thrusters, four on the corners and one in the centre, to provide the thrust to oppose the motion of the lander and cause it to decelerate. These would be fired during descent according to the requirement.
Isro would only use the thruster at the centre in the final minutes of touchdown to reduce the amount of lunar dust that could stick to the surface of the Lander and hamper its operations. “Rover Pragyan will have to wait for a few hours for the dust to settle before the ramp opens up and it starts to roll down," said Nirupam Roy, a professor at the Indian Institute of Science, Bangalore. “The lander’s orientation cannot change even slightly. Also, there is only a small window during which the orbiter would come above the lander, as its continuously revolving," said Roy.
The stakes are high as it is for the first time that India is executing a soft landing on the Moon. The success rate of soft landings on the Moon has so far been just 37%.
However, Isro is confident of doing this successfully, more so as the trans-lunar injections and lunar orbit insertion manoeuvres have gone precisely as planned and the orbit inclination to the lunar surface is accurate.
“We have done this before (simulating the manoeuvres)... However, the last part of mission is new to us," said Isro chairman K. Sivan.
“While we are far from a multi-planetary future, its prime early-stage technological requirement, in addition to the soft landing, is building effective mobile platforms for exploration of planetary bodies. It is why the Russian Lunokhod rovers were a big deal and so is the current Chang’e 4 rover Yutu 2. (The rover) Pragyan represents India’s first foray into designing a platform capable of traversing foreign landscapes and delivering good science. Much is expected of the two spectrometers on board Pragyan, which could find pristine materials from the lunar crust in the landing region, formed at least 3.8 billion years ago," said Jatan Mehta, a former science officer at TeamIndus.
The National Aeronautics and Space Administration of the US would be keenly watching the landing, as it has already announced its Artemis programme for exploring the south pole of the moon, where it eventually plans to set up a space station.
With the entire globe waiting for the data, a successful mission will guarantee India joining the US, Russia and China in being countries that have landed on the moon. If all goes as planned, India would be on the moon at 1:55 am on 7 September and announce how it plans to name the historic site near the south pole of the moon where no country has ever been before.
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