Chandrayaan-3 completes last Moon-bound manoeuvre; week to go for lunar landing

Chandrayaan-3 entered into the moon orbit on 5 August, following which orbit reduction manoeuvres were carried out on 6, 9 and 14 August.

BySouth First Desk

Published Aug 16, 2023 | 1:40 PMUpdatedAug 16, 2023 | 1:40 PM

Chandrayaan 3 closer to moon as it completes its final Moon bound manoeuvre

On Wednesday, 16 August, India’s ambitious Chandrayaan-3 spacecraft successfully executed its fifth and final moon-bound orbit manoeuvre, putting it even closer to the Moon’s surface.

ISRO’s third lunar expedition in 15 years, Chandrayaan-3 embarked on its month-long journey towards the moon on 14 July, piggybacking on the agency’s latest heavy-lift launch vehicle LVM3-M4 — nicknamed “Fat Boy” — from the spaceport Sriharikota in Andhra Pradesh.

With this, the spacecraft has completed all of its Moon-bound manoeuvres, and it will now prepare for the separation of the lander module—comprising the lander and rover — from the propulsion module.

“Today’s successful firing, needed for a short duration, has put Chandrayaan-3 into an orbit of 153 km x 163 km, as intended. With this, the lunar-bound manoeuvres are completed. It’s time for preparations as the Propulsion Module and the Lander Module gear up for their separate journeys,” ISRO said in a post on X (formerly Twitter).

Separation of the lander module from the propulsion module is planned for 17 August, it said.

Post its launch on 14 July, India’s third Moon mission Chandrayaan-3 entered into the lunar orbit on 5 August, following which orbit reduction manoeuvres were carried out on 6, 9 and 14 August.

As the mission progressed, a series of manoeuvres were conducted by ISRO to gradually reduce Chandrayaan-3’s orbit and position it over the lunar poles.

Also read: Orbit reduction manoeuvre brings Chandrayaan-3 closer to moon

Lander to ‘deboost’

After separation, the lander is expected to undergo a “deboost” (the process of slowing down) to place it in an orbit, where the Perilune (closest point to the Moon) is 30 kilometres and Apolune (farthest point from the Moon) is 100 km, from where the soft landing on the south polar region of the Moon will be attempted on 23 August, ISRO sources said.

ISRO chairman S Somanath recently said the most critical part of the landing is the process of bringing the velocity of the lander from 30 km height to the final landing, and that the ability to transfer the spacecraft from horizontal to vertical direction is the “trick we have to play” here.

The chairman further explains, “The velocity at the start of the landing process is almost 1.68 km per second, but this speed 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.

Further, it has to be ensured that fuel consumption is less, the distance calculation is correct, and all the algorithms are working properly, he added.

“Extensive simulations have gone, guidance design has been changed, and a lot of algorithms have been put in place to make sure that in all these phases required dispersions are handled…to attempt to make a proper landing,” he said.

Over five moves in the three weeks since the 14 July launch, ISRO had lifted the Chandrayaan-3 spacecraft into orbits farther and farther away from the Earth.

Also read: Chandrayaan-3 mission is in ‘normal health’, says ISRO

Chandrayan 3 to show capability in safe landing

Then, on 1 August in a key manoeuvre— a slingshot move— the spacecraft was sent successfully towards the Moon from Earth’s orbit. Following this trans-lunar injection, Chandrayaan-3 escaped from orbiting the Earth and began following a path that would take it to the vicinity of the Moon.

Chandrayaan-3 is a follow-on mission to Chandrayaan-2 (2019) to demonstrate end-to-end capability in safe landing and roving on the Moon’s surface.

It comprises an indigenous propulsion module, a lander module, and a rover with the objective of developing and demonstrating new technologies required for inter-planetary missions.

The propulsion module other than carrying the lander and rover configuration till about 100 km lunar orbit, has Spectro-polarimetry of Habitable Planet Earth (SHAPE) payload to study the spectral and polarimetric measurements of the Earth from the lunar orbit.

Also Read: ‘Fat boy’ blasts off with Chandrayaan-3, India’s hopes

Mission objectives

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

The lander will have the capability to soft land at a specified lunar site and deploy the rover that will carry out in-situ chemical analysis of the Moon’s surface during the course of its mobility.

The lander and the rover have scientific payloads to carry out experiments on the lunar surface.

Through the Chandrayaan 3 mission, scientists are aiming at mastering the technology of soft landing on the surface of the moon.

A successful mission would mean India becomes only the fourth country to accomplish the challenge, after the US, the former Soviet Union, and China.

About 16 minutes after lift-off, Chandrayaan 3 was separated from the rocket and orbited Earth a few times in an elliptical cycle — 170 km at its closest and 36,500 km at its farthest — before moving towards the lunar orbit.

A jubilant ISRO Chairman S Somanath said from the Mission Control Centre (MCC) that the rocket had injected Chandrayaan 3 into a precise orbit.

(With PTI inputs)