India's fourth lunar mission Chandrayaan-4 would not just soft land on the Moon, it will collect lunar samples, vertically liftoff from the Moon, and carry the samples to our home planet. For this ambitious venture, ISRO is working towards building two crafts, each of which weighs around 4,750kg. Instead of launching one massive craft, ISRO would launch two of these crafts into space using two LVM3 rockets. Thereafter, these crafts would have to perform docking and undocking in space as part of the mission, ISRO Chief Dr V Narayanan told WION's Sidharth MP. 

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The Indian Government has allocated Rs 2,104 crores (approx $240mn) for the Chandrayaan-4 mission, which is meant to collect and return samples from around the Moon's southern polar regions. According to India's Science and Technology Minister Dr Jitendra Singh, the target is to launch India's fourth lunar mission during October 2027.

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So far, only America, Russia, and China have executed Lunar sample return missions, with the most recent one being China's Chang'e-5 mission that returned samples from the dark side of the Moon. The dark side of the Moon is the region that is not visible from Earth. While multiple nations have attempted to land robotic crafts on the Moon to conduct in-situ studies, it must be emphasized that only limited equipment and sensors can be carried on the nearly 400,000km journey to the Moon, thus curbing the amount of studies that can be conducted there. Bringing back lunar samples to Earth can help test these samples in sophisticated and cutting-edge facilities, which can eventually offer a better understanding of the lunar samples, their characteristics and composition. 

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On WION's query about ISRO having to perfect docking technology in Earth orbit and lunar orbit ahead of Chandrayaan-4, Dr Narayanan said that the SPADEX satellites performing docking and undocking recently are steps in that direction. "I am happy to report that SPADEX is a grand success. We are going step-by-step. We have loaded each of the twin SPADEX satellites with 5kg of fuel and each satellite has 3.5kg of fuel remaining. Therefore, we can perform multiple docking-undocking and related experiments over the years and deliver the result."

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How Chandrayaan-4 will be executed 

According to ISRO, The Chandrayaan-4 mission would comprise five modules(components) - Ascender Module (AM), Descender Module (DM), Re-entry Module (RM), Transfer Module (TM), and Propulsion Module (PM). The five modules are planned to be launched as two crafts- DM + AM as one craft, and TM + RM + PM as the second craft. Two LVM3 rockets would be used to launch these crafts into orbit. 

After both launches are completed, the crafts will be docked together in an elliptical Earth orbit to form an integrated craft. Subsequent to docking, the Integrated craft will perform the first set of manoeuvres with the PM propulsion system. Once the PM is depleted, it gets jettisoned from the Integrated craft. The integrated craft (DM+AM+TM+RM) performs all the manoeuvres to achieve the lunar orbit. In the final lunar orbit, DM+AM gets separated from TM+RM, so that DM and AM then undergo powered descent to achieve soft landing on the lunar surface.

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After touchdown, a robotic arm, also called the Surface Sampling Robot mounted on the DM will scoop about 2 – 3 kg samples around the landing site and transfer it to a container on the AM. In addition, a drilling mechanism will collect sub-surface samples and transfer them to another container in the AM. The containers with samples will be sealed to prevent contamination and leakage during their journey to Earth. Various phases of sample collection operations will be monitored through video cameras.

Once sample collection is completed, AM would ascend to the lunar orbit and dock with the parked TM+RM. Samples will be transferred from AM to RM. After sample transfer, the TM+RM will be undocked from AM. Later, the TM + RM will perform maneuvers to return to Earth. At a suitable entry corridor, RM would get separated from TM and perform ballistic re-entry into Earth’s atmosphere and finally land onto Earth's landmass along with Lunar Sample. 

The Chandrayaan-4 mission aims to be entirely self-reliant, with all critical technologies developed domestically. Surface sampling, drilling mechanism, sample storage cartridge, sample transfer and docking are some of the new technologies which would be demonstrated in this mission. Indian industries will play a pivotal role in realizing this mission, which is expected to promote skill development, create significant employment opportunities and drive technological advancements. Chandrayaan-4 will pave the way for India's future manned missions, lunar sample return, and scientific analysis. It will also develop and demonstrate technologies, algorithms and operations for a mission that returns from the Moon back to the Earth, eventually enabling the planning of a mission to land Gaganyatris(Indian astronauts) on the Moon and bring them back safely.