A Mission in Five Pieces
Unlike its predecessors, Chandrayaan-4 is not a single spacecraft but a composite of five distinct modules designed to work in perfect harmony. This modular approach is necessary because a sample return mission involves multiple complex stages: landing,
collecting, ascending from the Moon, journeying home, and safely re-entering Earth's atmosphere. The mission is so massive, in fact, that it requires two separate launches using India's powerful LVM3 rocket. The modules will then perform a delicate docking manoeuvre in Earth orbit to form the integrated spacecraft before heading to the Moon.
The Descender and Ascender Duo
The first critical phase on the Moon involves two key modules: the Descender Module (DM) and the Ascender Module (AM). The Descender, building on the proven technology of Chandrayaan-3's Vikram lander, is tasked with making a precision soft landing. Once on the surface, it will deploy a robotic arm and a drill to collect several kilograms of lunar soil and rock. These precious samples will be transferred into the Ascender Module. After collection, the AM will perform the mission's most nail-biting manoeuvre: lifting off from the lunar surface, using the Descender as its launchpad to begin its journey back into lunar orbit.
An Orbital Rendezvous
While the lander duo is on the surface, two other modules will be waiting patiently in lunar orbit: the Transfer Module (TM) and the Re-entry Module (RM). The Ascender, carrying its priceless cargo, must flawlessly rendezvous and dock with the orbiting Transfer Module. This automated docking, happening hundreds of thousands of kilometres from home, is a critical technology ISRO is mastering for this mission. Once docked, the lunar samples are carefully transferred from the Ascender into the Re-entry Module for the final leg of the journey.
The Fiery Return to Earth
With the sample secured, the Transfer Module fires its engines to push the Re-entry Module out of lunar orbit and onto a trajectory towards Earth. The final piece of the puzzle is the Re-entry Module itself. This capsule is essentially a sophisticated heat shield, designed to protect the lunar samples as it plunges through Earth's atmosphere at extreme speeds. It must endure scorching temperatures and immense pressure to slow down and deliver its cargo safely back to scientists in India, making the nation only the fourth in history to achieve this remarkable feat.
