'Welcome, Buddy!': Chandrayaan-2 Orbiter Welcomes Chandrayaan-3 Lander Module, Two-Way Communication Established

On August 21, 2023, the Chandrayaan-2 orbiter formally welcomed Chandrayaan-3's lander module, and therefore, ISRO wrote on X that the orbiter told the lander module: 'Welcome, buddy!' 

Chandrayaan-3's lander module is now in a lunar orbit close to the Moon, and with Chandrayaan-2's orbiter. On August 21, 2023, the Chandrayaan-2 orbiter formally welcomed Chandrayaan-3's lander module, and therefore, the Indian Space Research Organisation (ISRO) wrote on X (formally Twitter) that Chandrayaan-2's orbiter told Chandrayaan-3's lander module: 'Welcome, buddy!' 

Since two-way communication has been established between the Chandrayaan-2 orbiter and Chandrayaan-3 lander module, the Mission Operations Complex (MOX) of ISRO Telemetry, Tracking and Command Network (ISTRAC), Bengaluru, has more routes to reach the lander module. 

ISRO also announced that the live telecast of the landing event will begin at 5:20 pm IST on August 23. Chandrayaan-3 is expected to land on the lunar south pole at around 6:04 pm IST on August 23. 

Earlier in the day on August 21, ISRO shared images of the lunar far side area, the side of the Moon that always faces away from Earth, captured by the Lander Hazard Detection and Avoidance Camera (LHDAC) on Chandrayaan-3's lander module. The function of the camera is to assist Chandrayaan-3 in locating a safe landing area on the Moon, during descent towards the lunar surface. The camera will help search for a landing area devoid of boulders and deep trenches. 

Chandrayaan-3's Journey Towards The Moon So Far

Chandrayaan-3's lander module underwent its second and final de-boosting operation on August 20 at 1:50 am IST, following which it reached an orbit of 25 km × 134 km. 

On August 17, the lander module and the propulsion module separated. 

The orbit-circularisation phase of Chandrayaan-3 began on August 16. This means that Chandrayaan-3 started to enter an orbit which is nearly circular in shape.

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 successfully lands on the Moon’s south pole, India will become the first country to softly land a spacecraft on the lunar south pole.