After the successful completion of Chandrayaan-3, ISRO is now focusing on Chandrayaan-4, which is a lunar sample-return mission. This involves making a soft landing on the Moon and bringing a sample of lunar rock back to Earth. If successful, India would become the fourth country, following the United States, Russia, and China, to accomplish this feat. The major objectives of the Chandrayaan-4 Mission are to achieve a safe and gentle landing on the lunar surface, collect and store lunar samples, lift off from the Moon's surface, dock and undock in lunar orbit, transfer samples between modules and then return to Earth.
The strategy for the Chandrayaan-4 Mission is intricate, involving five separate components of the spacecraft—the propulsion system, descender, ascender, transfer module, and re-entry module. This unique approach sets it apart from previous missions and is intended to aid in lunar exploration and the retrieval of samples from the Moon.
The five payloads or components include the Lunar Propulsion module which is designed to transport the Lunar lander and ascender stage to the Moon, much like the propulsion module used for Chandrayaan-3. There will be lunar lander that will touch down on the Moon carrying instrumentation to support the ascend stage and soil sampling equipment. There will also be a Lunar Module Ascender which, after collecting and storing samples from the Moon, will detach from the lander and take off from the lunar surface, utilizing the lander as a launching platform to enter a low-lunar orbit. It will also have a transfer module that will gather samples from the ascend stage and will transport them to the reentry module, activating its engine to propel both modules towards Earth, releases the payload, and then loop back around the Earth. The reentry module will contain the lunar samples (which is called as Lunar Regolith mixture of rocks and soil) collected from orbit and is built to withstand reentry into Earth's atmosphere, landing safely with the lunar soil.
“Chandrayaan-4 will be unique in that it will utilize two different rockets: the heavy lifter Launch Vehicle Mark-3 (LMV-3) for carrying most of the payloads, and the dependable work horse Polar Satellite Vehicle (PSLV). These rockets will be launched on different dates, with the earliest launch not expected before 2028. ISRO will utilize two different rockets to launch the components of the spacecraft. The LVM-3 will carry the propulsion, descender, and ascender modules, while the regular PSLV will transport the transfer module and re-entry modules to their designated lower lunar orbits. ISRO is yet to determine the sequence,” explained space expert Girish Linganna.
He said the the descender module will use a robotic arm to gather lunar samples, which are then transferred to the Ascender Module. The Ascender Module then separates and ascends to lunar orbit to dock with the Transfer Module. This creates a combination of Ascender, Transfer, and Re-entry modules in lunar orbit.
“The Transfer Module moves the lunar samples from the Ascender Module to the Re-entry Module, then the Ascender Module detaches from the three-part structure (Ascender, Transfer, and Re-entry modules structure). The combined Transfer and Re-entry modules will return to Earth orbit. The Re-entry Module will then detach from the Transfer module in a suitable Earth-bound orbit and re-enter Earth's atmosphere to land safely,” added Linganna.
The successful docking of the Ascender Module with the Transfer Module in lunar orbit will depend on the completion of the planned Space Docking Experiment (SPADEX). This mission, developed by ISRO, involves two spacecraft and aims to advance technologies for orbital rendezvous (or Orbital Meeting), docking, and formation flying.
