‘Smooth sailing’ as Chandrayaan-3 touches down tomorrow - The Indian Express

A wave of anticipation swept the country as the Lander Module of Chandrayaan-3 prepared to make a “safe and soft landing” on the surface of the Moon Wednesday evening.

If all goes to plan, the Moon landing will make India the first country to land a spacecraft on the lunar south pole, the finest moment till date of its space programme — and end the disappointment over the crash-landing of the Chandrayaan-2 lander four years ago.

The ISRO, in a social media post Tuesday, said the Mission Operations Complex (MOX) has been buzzing with “energy” and “excitement”.

“The mission is on schedule. Systems are undergoing regular checks. Smooth sailing is continuing,” ISRO said.

The Chandrayaan-3 lander is scheduled to make a touchdown at 1804 hours IST Wednesday, after 17 minutes of descent from the pre-landing lunar orbit it is currently in.

ISRO’s Telemetry Tracking and Command Centre (ISTRAC) in Bengaluru will issue a command at 1747 hours that will signal the spacecraft to begin the descent.

From a velocity of about 6,000 km/hour in the orbit, the spacecraft will have to slow down to near zero as it makes a touchdown. It is designed to land safely even at speeds of 10 km/hour.

The descent will be completely autonomous – artificial intelligence and computer logic driven – with the mission control at ISTRAC keeping a close watch.

Chandrayaan

The final approach will be a heady cocktail of anxiety, nervousness and anticipation. It was in these last moments that Chandrayaan-2 developed problems and fell on the Moon’s surface. Four missions, including Luna-25 of Russia two days ago, have met a similar fate in the last four years.

ISRO has added several layers of safeguards to ensure that an incident like the previous one does not recur. As of Tuesday, it was – to quote the ISRO – “smooth sailing”.

Mission control in Bengaluru will receive data on signals sent by the Chandrayaan-3 lander directly to ground stations at the Deep Space Network in Bengaluru, the Jet Propulsion Laboratory in the US and a European Space Agency station in Spain or via the Chandrayaan-2 orbiter with which Chandrayaan-3 established contact Monday, according to ISRO.

Mission control cannot, however, send commands to the lander once the descent phase begins. After the start of the descent, the lander will have to use its programmed AI to make a “safe and soft landing”.

ISRO chairman S Somanath has said that the Chandrayaan-3 lander is designed with a failure-based approach – meaning thereby that every kind of failure eventuality has been accounted for and layers of safeguards have been built in.

The spacecraft’s legs have been strengthened so that it can land safely even at greater speeds, its software has been updated, its fuel capacity increased, and its ability to manoeuvre and find a suitable place to land has been expanded.

In a recent public talk, Somanath, disclosing the exact reason for the failure of Chandrayaan-2, said the spacecraft had generated more than optimum thrust in the final stages of landing, and that the onboard software’s error-correcting mechanism was not designed to attend to this immediately but only after completion of a certain cycle of tasks.

As a result, the errors accumulated and by the time the computer attempted to correct these, the errors had bloated and could no longer be corrected, he said. These kinds of anomalies in the software have been rectified in Chandrayaan-3.

“The core of Chandrayaan-3 is its sensors. When you have something that is remotely operated, then everything depends on its ability to sense its location, what is its speed, what is the orientation. There are different sensors used for this purpose. There are the velocimeters and altimeters which give a reference for the speed and the height of the lander,” he said.

“There is a camera called a hazard-avoidance camera, there are also inertia-based cameras. The sensors are fused together using a computer algorithm to provide an indication of where the lander is positioned. This has been tested extensively,” he said.

The Chandrayaan-3 lander is aiming to land at the start of daytime on the Moon, which extends to 14 Earth days. The instruments on the spacecraft are all solar powered and are designed to function for one lunar day, or a 14-day period on Earth.

A senior ISRO official said Monday that in case the spacecraft, for some reason, is not ready to make a landing Wednesday, another landing attempt could be made on August 27.

However, on earlier occasions, Somanath said that in order to give the instruments ample time to carry out observations and experiments on the lunar surface, it was important to make the landing at the start of daytime. That meant that if for some reason, landing is not possible on August 23 or 24, the spacecraft will wait for about one month – 14 days of lunar day and another 14 for lunar night – before making the second attempt.

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‘Smooth sailing’ as Chandrayaan-3 touches down tomorrow - The Indian Express

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