Chandrayaan-3: ISRO prepared to postpone Moon touchdown to 27 August if lander health deemed ‘abnormal’

With the mission being on schedule, ISRO has currently planned the soft landing of the Chandrayaan-3 spacecraft at 6:04 pm IST on 23 August.

BySumit Jha

Published Aug 22, 2023 | 8:41 PMUpdatedAug 22, 2023 | 8:42 PM

Earlier, ISRO had said that the touchdown would take place at 5:47 pm on 23 August. (Supplied)

The nation waits with bated breath as scientists at the Indian Space Research Organisation (ISRO) gear up for the much-awaited soft landing of the Chandrayaan-3 spacecraft on the surface of the Moon at 6.04 pm on Wednesday, 23 August.

The wait, however, could be longer.

The space agency may consider postponing the touchdown to 27 August in the event that the “health parameters” of the lander module are found to be “abnormal”, a senior official said on Tuesday.

ISRO prepared for changes

According to ISRO Space Applications Centre Director Nilesh Desai, the focus of the scientists would be on reducing the speed of the spacecraft above the lunar surface.

“The lander will try to land on the Moon’s surface from a height of 30 km on 23 August and its velocity at that time should be 1.68 km per second. Our focus will be on reducing that speed because the Moon’s gravitational force will also play its part,” he told PTI, in Ahmedabad.

“If we do not control that speed, there will be chances of a crash landing. If any health parameter (of the lander module) is found abnormal on 23 August, then we will postpone the landing to 27 August,” he said.

The space agency said that the Mission Operations Complex (MOX), located at the ISRO Telemetry, Tracking and Command Network (ISTRAC), in Bengaluru, is buzzing with energy and excitement.

“The mission is on schedule. Systems are undergoing regular checks. Smooth sailing is continuing,” ISRO said in an update this afternoon, adding that the live telecast of the landing operations at MOX/ISTRAC will begin at 5.20 pm on Wednesday.

Chandrayaan-3’s lander module’s soft landing on the lunar surface would put India in an elite club of countries that have achieved the feat of reaching the Moon’s surface — the United States, erstwhile Soviet Union, and China are currently on that list.

Related: ISRO says Lander’s health normal, releases images of the Moon

The mission

The lander module (LM), comprising the lander “Vikram” and the rover “Pragyan”, is scheduled to make a touchdown near the south polar region of the Moon.

If the Chandrayaan-3 mission succeeds in making a touchdown on the Moon and in landing a robotic lunar rover in ISRO’s second attempt in four years, India will become the fourth country to master the technology of soft-landing on the lunar surface.

Chandrayaan-3 is a follow-on mission to Chandrayaan-2 and its objectives are to demonstrate safe and soft-landing on the lunar surface, roving on the Moon, and to conduct in-situ scientific experiments.

Chandrayaan-2 had failed in its lunar phase when its lander “Vikram” crashed onto the surface of the Moon, following anomalies in the braking system while attempting a touchdown on 7 September, 2019. Chandrayaan’s maiden mission was in 2008.

The ₹600-crore Chandrayaan-3 mission was launched on 14 July onboard the Launch Vehicle Mark-III (LVM-3) rocket, for a 41-day voyage to reach near the lunar south pole.

The soft landing is being attempted days after Russia’s Luna-25 spacecraft crashed into the Moon after spinning out of control.

After the second and final deboosting operation on 20 August, the LM is placed in a 25 km x 134 km orbit around the Moon.

The module would undergo internal checks and await sunrise at the designated landing site, ISRO said, adding that the powered descent — to achieve soft-landing on the Moon’s surface — is expected to be initiated at around 5.45 pm on Wednesday.

Also Read: Chandrayaan 3 starts lunar exploration journey

’17 minutes of terror’

ISRO released images of the Moon as captured by the Lander Position Detection Camera (LPDC) of the Chandrayaan-3 mission on 19 August and by Lander Imager Camera 4 on 20 August.

LPDC images assist the LM in determining its position (latitude and longitude) by matching them against an onboard moon reference map, according to the Bengaluru-headquartered national space agency.

The critical process of soft landing has been dubbed by many including ISRO officials as “17 minutes of terror”, with the entire process being autonomous when the lander has to fire its engines at the right times and altitudes, use the right amount of fuel, and scan of the lunar surface for any obstacles or hills or craters before finally touching down.

After checking all the parameters and deciding to land, ISRO will upload all the required commands from its Indian Deep Space Network (IDSN) at Byalalu, Karnataka, to the LM, a couple of hours before the scheduled time touchdown..

According to ISRO officials, for landing, at around 30 km altitude, the lander enters the powered braking phase, and begins to use its four thruster engines by “retro firing” them to reach the surface of the Moon, by gradually reducing the speed.

Noting that on reaching an altitude of around 6.8 km, only two engines will be used, shutting down the other two, aimed at giving the reverse thrust to the lander as it descends further, they said.

Then, on reaching an altitude of about 150-100 metres, the lander, using its sensors and cameras, will scan the surface to check whether there are any obstacles and then start descending to make a soft landing.

Also Read: Lander Module of Chandrayaan-3 successfully separates

Critical part of the mission

ISRO Chairman S Somanath had recently said that the most critical part of the landing will be the process of reducing the velocity of the lander from 30 km height to the final landing, and the ability to reorient the spacecraft from horizontal to vertical direction.

“This is the trick we have to play here,” he said.

“The velocity at the starting of the landing process is almost 1.68 km per second, but at this speed, the lander is horizontal to the surface of the Moon. Chandrayaan-3 here is tilted almost 90 degrees, it has to become vertical. So, this whole process of turning from horizontal to vertical is a very interesting calculation, mathematically. We have done a lot of simulations. It is here where we had the problem last time (Chandrayaan-2),” Somanath explained.

After the soft landing, the rover will descend from the lander’s belly onto the Moon’s surface using one of its side panels, which will act as a ramp.

The lander and rover will have a mission life of one lunar day (about 14 Earth days) to study the surroundings there. However, ISRO officials do not rule out the possibility of them coming to life for another lunar day.

The lander will have the capability to soft-land at a specified lunar site and deploy the rover, which will carry out in-situ chemical analysis of the lunar surface during the course of its mobility. The lander and the rover have scientific payloads to carry out experiments on the lunar surface.

“After powered descent on to the landing site, there will be deployment of ramp and rover coming out. After this, all the experiments will take place one after the other — all of which have to be completed in just one day on the Moon, which is 14 days,” Somnath said.

Noting that as long as the Sun shines, all the systems will have its power, he said, “The moment the Sun sets, everything will be in pitch darkness, temperature will go as low as minus 180 degree Celsius; so it is not possible for the systems to survive. And if it survives further, then we should be happy that once again it has come to life and we will be able to work on the system once again, and we hope like that to happen.”

Polar regions of the Moon are a very different terrain due to the environment and the difficulties they present and, therefore, have remained unexplored. All the previous spacecraft to have reached the Moon landed in the equatorial region, a few degrees latitude north or south of the lunar equator.

Also Read: Chandrayaan-3 moon quest carries the hopes of a nation

(With PTI inputs)