Chandrayaan-3's Lander Module Undergoes Final De-Orbiting Manoeuvre, Descent Towards Lunar Surface To Begin On Aug 23

Chandrayaan-3: The de-boosting operation of the lander module occurred at 1:50 am IST on August 20, 2023. The lander module is now in an orbit of size 25 km × 134 km, and spacecraft health is normal.

Chandrayaan-3’s lander module has undergone its second and final de-orbiting manoeuvre, and is now in an orbit of size 25 km × 134 km. This de-boosting operation occurred at 1:50 am IST on August 20, 2023. The Indian Space Research Organisation (ISRO) said in a mission update that spacecraft health is normal.

Next, the lander module, which consists of the Vikram lander and the Pragyan rover, will undergo internal checks and wait for sunrise to occur at the designated landing site.

The de-boosting operation is important because it has allowed the lander module to reach the orbit from which the spacecraft can start its descent towards the lunar surface.

According to ISRO, the lander module is expected to land on the lunar surface on August 23, between 5:30 pm to 6:30 pm IST.

The lander module’s first de-orbit manoeuvre occurred on August 18, 2023.

Chandrayaan-3’s lander module separated from the propulsion module on August 17, 2023, at 1:15 pm IST. The lander module will descend to a slightly lower orbit following a de-boosting operation set to occur on August 18, at around 4:00 pm IST. After the separation of the lander module and the propulsion module, ISRO wrote on X (formerly Twitter) that the lander module said to the propulsion module: ‘Thanks for the ride, mate! 👋’

With the separation of the lander module and the propulsion module, there are three Indian spacecraft orbiting the Moon. These are: Chandrayaan-2’s orbiter, and Chandrayaan-3’s lander module and propulsion module.

While the mission life of the propulsion module is three to six months, the lander module is expected to operate only for 14 Earth days, or one lunar day. ISRO wrote on X on August 17 that the propulsion module may continue its journey in lunar orbit for up to a year.

The propulsion module is equipped with a payload called Spectro-polarimetry of Habitable Planet Earth (SHAPE). The function of SHAPE is to study the spectral and polarimetric measurements of Earth from lunar orbit. This means that SHAPE will analyse the spectro-polarimetric signatures of Earth.

According to the University of Maryland, Baltimore County (UMBC) Observatory, spectro-polarimetry is a technique which involves the polarisation of light by splitting the incoming light into its constituent colours, and then analysing the polarisation of each colour individually.

Understanding the spectro-polarimetric signatures of Earth can help scientists analyse the reflected light from exoplanets and determine whether they would qualify for habitability.

In other words, the SHAPE payload will accumulate signatures of exoplanets that may have features which qualify it for the habitability of humans.

The Unnao Rao Space Centre in Bengaluru has designed the SHAPE payload.

The propulsion module weighs 2,148 kilograms, and has a power generation capacity of 758 Watts.

The lander module has a mass of 1,752 kilograms, and a power generation capacity of 738 Watts.

The Vikram lander’s payloads are Chandra’s Surface Thermophysical Experiment (ChaSTE), Instrument for Lunar Seismic Activity (ILSA), Laser Retroreflector Array (LRA) Rover, and Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere (RAMBHA).

ChasTE will carry out measurements of thermal properties such as thermal conductivity and temperature of elements on the lunar surface near the south pole; ILSA will measure the seismicity around the landing site and describe the structure of the lunar crust and mantle; and RAMBHA will study the gas and plasma environment.

The rover is equipped with two payloads, which are the Alpha Particle X-ray Spectrometer (APXS), and Laser Induced Breakdown Spectroscope (LIBS).

APXS will help determine the elemental composition of the lunar soil and rocks around the landing site. The elements to be studied include magnesium, aluminium, silicon, potassium, calcium, titanium and iron.

LIBS will conduct qualitative and quantitative elemental analysis in order to infer the chemical and mineralogical composition of the lunar surface.

If Chandrayaan-3 lands on the Moon’s south pole before Russia’s Luna 25, India will become the first country to softly land a spacecraft on the lunar south pole.