India's next Moon mission will be modular: Chandrayaan-4 to assemble in space

Indian Space Research Organization (ISRO) is targeting a two-phased launch for Chandrayaan-4 in 2028. The mission will use Next Generation Launch Vehicle (NGLV) to carry pre-built modules into space over two phases, where they will be assembled in orbit to complete the spacecraft. Chandrayaan-4 is expected to bring back rock samples from the Moon’s surface. 

The weight of Chandrayaan-4 is expected to exceed the payload capacity of even the most powerful rockets, which is why ISRO plans to launch the spacecraft in two phases. Each module is expected to weigh over 200kg. 

“We have worked out the configuration of Chandrayaan-4. How to bring back samples from Moon to Earth. We propose to do it with multiple launches because our current rocket capability is not enough to do it at one go,” said S Somanath, chairman of ISRO, at an event in New Delhi.

“So, we have to have docking capability in space, both in Earth space as well as in Moon space. We are developing that capability. We have a mission called Spadex scheduled later this year to demonstrate this capability,” Somanath added.

Spadex, short form for space docking experiment, is a twin spacecraft mission that will test autonomous orbital rendezvous, formation flying techniques and docking capabilities, which are expected to be used in the launch of Chandrayaan-4. The total cost of the mission is estimated to be around 125 crore. 

In addition to the next lunar mission, ISRO is also eyeing India’s first space station. Somanath said that the space agency has completed the proposal for Bhartiya Antriksh Station (BAS) and is planning to submit it to the central government soon for approval.

ISRO has also submitted for government approval the design, configuration, production and cost estimates for NGLV, which will replace the much heavier Launch Vehicle Mark 3 (LVM-3). 

While Chandrayaan-4 will be India's first venture into assembling spacecraft in space, this technique has been used before.   

The International Space Station (ISS) was the first spacecraft that was assembled in space.  Its  sheer size and weight made it unfeasible for any rocket at that time or even now to launch the entire station in one piece.  Various modules of the ISS were carried to space in multiple missions by various space agencies and assembled in orbit.

The first module was launched in 1998 and the assembly was completed in 2011. 

India achieved significant milestones in space exploration when it launched the Chandrayaan-3 mission in July 2023. It was the first lunar mission by any country to land on the Moon's south pole, which has a rougher terrain that makes smooth landing more challenging. Also, the temperature in the south pole is much lower and can plummet to as low as -230 degree celsius.

The main objective of Chandrayaan-3 was to demonstrate safe and soft landing on the Moon’s surface. It also made India only the fourth country after the US, erstwhile Soviet Union and China to land on the Moon. 

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