Chandrayaan-3 lander separates from propulsion module: What happens next?

Chandrayaan-3 is India’s second attempt at carrying out a “soft landing” on the lunar surface, after Chandrayaan-2 crashed during the final landing manoeuvre.

Chandrayaan-3 Mission:

‘Thanks for the ride, mate! 👋’
said the Lander Module (LM).

LM is successfully separated from the Propulsion Module (PM)

LM is set to descend to a slightly lower orbit upon a deboosting planned for tomorrow around 1600 Hrs., IST.

Now, 🇮🇳 has3⃣ 🛰️🛰️🛰️… pic.twitter.com/rJKkPSr6Ct

— ISRO (@isro) August 17, 2023

We tell you what happens next.

Lander will slowly descend further

As per Isro, the lander module will descend further towards the lunar surface from the current near-circular orbit of 153 x 163 km after a de-boosting manoeuvre planned for tomorrow evening.

In total, the lander will carry out two orbit-reduction manoeuvres on its own, first getting into the circular 100 x 100 km orbit, and then further closer to the moon in the 100 x 30 km orbit. It is from this orbit, on August 23, that the lander will begin its final descent to make a touchdown on the moon.

The challenge of soft landing

Chandrayaan-2, India’s previous attempt at putting a rover on the moon, went as per expectation till the final few moments of the landing. Both software and hardware deficiencies impeded the lander from reducing its speed as required for a soft landing.

Soft landings on bodies in space are extremely difficult, requiring advanced technical capabilities to achieve.

Amitabha Ghosh, a scientist for NASA’s Rover mission to Mars, explained in The Indian Express: “Imagine a spacecraft hurtling through space, at 10 times the speed of an airplane, having to nearly come to a standstill in order to land gently … all in the matter of a few minutes and, more importantly, without any human intervention. This, in a nutshell, is a soft landing.”

Chandrayaan-3’s lander module has made notable updates to achieve a soft landing this time. It has reinforced legs/stilts to help sustain harder than anticipated impact, more instruments and updated software with multiple redundancies to be able to better deal with unforeseen circumstances, and a bigger fuel tank – crucial in case any last minute changes have to be made.

“We have done whatever we could think of in terms of probabilities in the last two years and it is with this confidence that we are moving to launch Chandrayaan-3,” ISRO chairman S Somanath had said at the time of the launch.

Scientific missions on the lunar surface

Once the lander module has successfully touched the surface of the moon, the rover will be deployed.

There are two payloads on the rover, designed to study the chemical and mineral composition of the lunar surface and to determine the composition of elements such as magnesium, aluminium and iron in the lunar soil and rocks.

The Chandrayaan-3 rover is set to operate for one lunar day – 14 earth days – only. This is because it lacks the thermal insulation required to survive in the frigid temperatures of the lunar night.

The lander too has four scientific payloads: to study lunar quakes, thermal properties of the lunar surface, changes in the plasma near the surface, and a passive experiment to help accurately measure the distance between Earth and moon. The fourth payload comes from NASA.

But what about the propulsion module?

While the focus now will firmly be on the lander and the rover, the propulsion module will continue orbiting the moon and studying the spectral signatures of Earth using a payload that was tacked on to the mission in addition to the science experiments carried on board its predecessor.

By studying Earth from the moon, the Spectro-polarimetry of Habitable Planet Earth (SHAPE) will help scientists understand the markers of life on exoplanets.

Even after the lander and rover have exhausted their capabilities to operate, the propulsion module can run for years. “Meanwhile, the Propulsion Module continues its journey in the current orbit for months/years,” Isro said.