Chandrayaan-3 ready to make history as ISRO says mission on schedule

The Lander Module (LM) of Chandrayaan-3, ISRO's ambitious third Moon mission, is set to land on the lunar surface on Wednesday evening as India seeks to become the first country to reach the uncharted south pole of Earth's only natural satellite.

The ISRO has confirmed that the landing of Chandrayaan-3 is on schedule and that the lander is undergoing regular checks. The ISRO also said they will organise a live telecast of the landing process, which will begin at 5.20 pm on the same day. The link for the livestreaming has also been shared and is available on ISRO’s official website.

The LM, comprising the lander (Vikram) and the rover (Pragyan), is expected to make a soft-landing near the south polar region of the Moon at 6:04 pm. This will be the Indian Space Research Organisation’s (ISRO) second attempt in four years to land on the Moon.

If the mission succeeds in making a touchdown and in landing a robotic lunar rover, India will become the fourth country to master the technology of soft-landing on the lunar surface after the US, China and the erstwhile Soviet Union.

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

Moon images released

ISRO on Tuesday released images of the Moon captured by the Lander Position Detection Camera (LPDC) of the Chandrayaan-3 mission from an altitude of about 70 km on August 19.

LPDC images assist the Lander Module (LM) of the mission, scheduled to make a soft-landing on the Lunar surface on Wednesday, in determining its position (latitude and longitude) by matching them against an onboard moon reference map, the Bengaluru-headquartered national space agency said. The ISRO on Monday released images of the lunar far side area captured by the Lander Hazard Detection and Avoidance Camera (LHDAC). This camera that assists in locating a safe landing area -- without boulders or deep trenches -- during the descent is developed by Ahmedabad-based Space Applications Centre (SAC), a major research and development centre of ISRO.

According to ISRO, to achieve the mission objectives of Chandrayaan-3, several advanced technologies are present in the Lander such as LHDAC. Chandrayaan-3, launched on July 14, is a follow-on mission to Chandrayaan-2 to demonstrate end-to-end capability in safe landing and roving on the lunar surface.

‘Terror landing’

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 near Bengaluru, to the LM, 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.

This is to ensure the lander doesn’t crash, as the Moon’s gravity will also be in play.

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.

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

Cutting velocity

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

“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. The 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.

Polar regions

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. The Moon’s south pole region is also being explored because there could be a possibility of presence of water in permanently shadowed areas around it.

Ahead of its scheduled landing on the moon, Chandrayaan-3’s LM has established a two-way communication with Chandrayaan-2’s orbiter which continues to orbit around the Moon.

Meanwhile, the Propulsion Module, whose main function was to carry the Lander Module from launch vehicle injection till lander separation orbit, will continue its journey in the current orbit for months/years, the space agency said.

Chandrayaan-2 failure

Chandrayaan-2 failed in its lunar phase when its lander ‘Vikram’ crashed into the surface of the Moon following anomalies in the braking system in the lander on September 7, 2019.

Chandrayaan’s maiden mission was in 2008.

The Rs 600 crore Chandrayaan-3 mission was launched on July 14 onboard a Launch Vehicle Mark-III (LVM-3) rocket, for a 41-day voyage.

Only days earlier, Russia's Luna-25 spacecraft crashed into the Moon after spinning out of control.

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

The module would undergo internal checks and await the sunrise at the designated landing site, ISRO has 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.

(With agency inputs)