Chandrayaan 4 will bring unique Moon materials—and maybe a giant scientific leap for India

It’s been a year since the approval of ISRO’s Chandrayaan 4 mission, and ISRO has not yet provided an update on if the preliminary design review (PDR) to finalize the mission design has been completed—especially when considering that the original announcement stated 2027 as the target launch year. The word on the street from multiple sources is that Chandrayaan 4’s PDR is done or near complete but multiple media queries and follow-ups sent to ISRO continue to not be answered.

That it’s the tax season in India is reminding space industry observers and participants here that ISRO doesn’t consistently share about key milestones associated with the publicly funded civil space exploration missions. The limited official information on Chandrayaan 4 remains scattered online and offline, and is even inconsistent with each other at times. As a result, it’s frequently taken and presented out of context by the media and the space industry at large, causing more misunderstandings of the mission’s goals and potential.

Based on confirmed but scattered public sources, I want my readers and people worldwide to know about India’s fascinating Chandrayaan 4 mission in one convenient place. This article is thus my attempt to collate, clarify, and adequately contextualize everything we know about ISRO’s actual plans for Chandrayaan 4. I also explain the mission’s immense scientific potential in the global context, and propose the idea of India doing a sample exchange with China and the US for the benefit of both nations and their researchers. ISRO responding to media queries would’ve helped put together a better article but here goes all that I could assemble anyway.

The mission

Chandrayaan 4 will fetch samples from the Moon’s south pole for researchers worldwide. Now launching by 2028, the mission was approved with a budget of ₹2104 crores ($252 million) last September by the Indian Government Union Cabinet following Chandrayaan 3’s triumphant touchdown on the Moon in August 2023. Chandrayaan 4 currently aims to bring two kilograms of scooped plus drilled samples for scientific studies to enrich our understanding of the Moon. Using combined imagery and topographic data from the Chandrayaan 2 orbiter and NASA’s Lunar Reconnaissance Orbiter, the mission’s landing site being evaluated is between 84-85° on the lunar south pole, which has the potential for hosting buried water ice deposits.

The Chandrayaan 4 mission comprises five spacecraft modules:

• the lander (descender module)
• the propulsion module
• the ascender module
• the sample transfer module
• and the Earth reentry capsule module.

ISRO will launch these modules in two stacks, each currently weighing about 4600 kilograms. However, each stack’s mass still lies beyond the reach of India’s current most powerful rocket, the Launch Vehicle Mark III (LVM3), which launched Chandrayaan 3. That’s why ISRO’s launch vehicle of choice for Chandrayaan 4 is an upgraded version of LVM3 whose core stage will be powered by the upcoming SE2000 semi-cryogenic kerolox engine. The LVM3’s lift capacity to GTO orbit would then be increased from about 4200 kilograms to roughly 5000, allowing an LVM3 each to launch a Chandrayaan 4 stack while also allowing some margin for mass changes during development. ISRO has said this maxed out LVM3 rocket will be ready to fly in 2027.

During the Chandrayaan 4 mission, each spacecraft stack will be deployed in an elliptical Earth orbit. The two launches will be within a month of each other. The stacks then rendezvous and dock with each other in Earth orbit to form a full, integrated stack. The large propulsion module then raises the stack’s Earth orbit, approaching closer to the Moon and jettisoning itself post that. The remainder stack then enters lunar orbit, where the lander plus ascender module separate out for descent and land on the Moon’s south pole. A robotic arm will collect and transfer scooped plus drilled samples into a sealed container. Only the ascender module carrying these samples then lift off to lunar orbit. After docking with the stack that stayed back in lunar orbit, the samples will be transferred to the reentry capsule module to get them to Earth with a tactful reentry and oceanic splash.

Pre-Chandrayaan 4 preparations

With Chandrayaan 3, one of the extended goals ISRO achieved was pulling the mission’s propulsion module from lunar orbit back to Earth orbit, thereby demonstrating a small but key capability that will be required to pull off a robotic sample return with Chandrayaan 4. One of the most complex parts of Chandrayaan 4 would be to remotely dock large robotic modules in Earth and lunar orbit. The latter is a feat only China has achieved so far with their Chang’e 5 and Chang’e 6 sample return missions respectively.

Because Chandrayaan 4 is a huge technological leap for India, ISRO is taking the approach of demonstrating and practicing docking satellites in Earth orbit first to reduce risks. Earlier this year, the first such milestone was accomplished when India’s $14 million SPADEX satellites successfully docked and then later undocked in circular Earth orbit. ISRO continues testing dual-satellite operations and precision approaches with the satellites.

M. Sankaran, the Director of ISRO’s key URSC center in Bangalore—which was involved in Chandrayaan 3’s design, assembly, and testing—has told asianetnews that the upcoming SPADEX 2 mission will demonstrate docking in elliptical orbit, the same kind that the two Chandrayaan 4 spacecraft stacks will also need to execute. To further mimic a Chandrayaan 4 like mission scenario, the SPADEX 2 satellites and their docking ring sizes will be bigger than the first pair. SPADEX 2 has gotten mission approval from the Indian government, and is now awaiting a financial sanction.

The scientific value of Chandrayaan 4 samples

NASA’s Apollo missions helped scientists confirm that our celestial companion had a fiery origin tied to Earth. On the other hand, the Soviet Luna missions were the world’s first robotic sample return missions, establishing the modern approach that fetching planetary material to Earth generates scientific results for decades. Samples fetched by China’s robotic Chang’e 5 mission confirmed that the Moon was volcanically active and thermally complex geologically recently. And Chang’e 6 transformed our understanding of how our Moon evolved thanks to the first ever samples from the mysterious lunar farside.

As I wrote in my article ‘Why explore our Moon’, for us to continue piecing together the complex and nuanced origin and evolution of the Earth-Moon system, we need to continue fetching distinct geological material so that our world’s lunar samples represent more of the Moon—a trend started by Chang’e missions. We currently don’t have any samples from the lunar poles, including potential water ice or water-mixed regolith from there. It’s important to understand this water’s sources, its abundance, and how it is related or unrelated to Earth’s water. Said knowledge is equally crucial in helping us plan sustained lunar exploration and build future Moonbases. As such, when Chandrayaan 4 brings unique lunar polar samples to Earth, it will help humanity make its first tactile advances into these fundamental open questions about our Moon, Earth, Solar System, and future in space.

Related tangent: I’m pleased that ISRO’s webpage on Chandrayaan 4 cites my blog as a reference for the mission’s scientific context! 🚀

Many thanks to Open Lunar Foundation, Takshashila Institution, PierSight and Gurbir Singh for sponsoring this week’s special combined edition of Moon Monday and Indian Space Progress!

If you too appreciate my efforts of putting together this curated & unique resource on Chandrayaan 4 for free, and without ads, kindly support my independent writing:

Prepping for Chandrayaan 4 science

For a nation that began planetary exploration only this century starting with Chandrayaan 1, a sample return mission will be a giant leap in scientific output. To ensure tapping into its potential though, ISRO has recognized that early preparations would be needed across the board. Some representative developments to that end are listed below.

• In April, ISRO gathered about 50 scientists from across India to deliberate on and help determine next steps for storage and scientific studies of lunar samples Chandrayaan 4 will fetch.
• The ISRO-affiliated PRL institute conducted an in-person inaugural workshop for students last November to teach them via lab visits and hands-on sessions how to handle and analyze space and planetary samples. More such workshops are planned not just for students but for professional scientists across the country since realizing Chandrayaan 4 necessitates building national capacity to thoroughly prepare, store, curate, characterize, and analyze the first set of space samples fetched by India. The second such workshop is yet to take place.
• An official response this past August to a query put forth in the Rajya Sabha—loosely, the Indian equivalent to the US Senate—provides us some details on how ISRO is planning the handling and storage of Chandrayaan 4 samples:

Chandrayaan-4 mission will ensure the safe handling and storage of lunar sample to prevent contamination by transferring the leak proof sample canisters to sample curation facility with contamination control features. Establishment of Curation Facility (Class 100 & 1000 clean room environment as per ISO standard) is planned with advanced instrument[s] to preserve the integrity of the sample for scientific analysis. As per COSPAR (Committee on Space Research) Planetary Protection policy, lunar missions fall under the category where it does not demand stringent requirement for biological contamination.

The case for India to study and exchange Chang’e lunar samples

In April, China announced the first set of international researchers whose proposals were selected to study unique lunar samples brought to Earth by Chang’e 5 in 2020. The researchers now analyzing said samples are from universities or institutes in the UK, Japan, France, Germany, Pakistan, and even the US (through efforts outside of NASA). Unfortunately, ISRO or its affiliated institutions did not participate in these sample research proposals. In fact, no non-ISRO or non-government funded Indian institute proposed Chang’e 5 sample studies either in this round.

Sure, India and China aren’t on friendly terms but so aren’t US and China, and yet recognizing the scientific value of Chang’e 5 samples, NASA did secure a remarkable exception to the Wold Amendment from the US Congress for the country’s researchers to be able to apply for federally funded Chang’e sample research proposals. While the latter outcome remains blocked from the US’ own side, getting the Congressional exception was the first big step in the right direction. India doesn’t have a Wolf Amendment of its own, and so no major legal blockers exist for national research institutes or otherwise to study Chang’e samples. Besides, India and China do have relations & interactions for trade, economic growth, infrastructure contracts, and several technologies out of necessity for both nations. So why should science be the one excluded of all things?

Several Indian scientists, like those at the ISRO-affiliated PRL institute, have already studied Apollo and Luna samples. They have studied asteroid samples too. As such, Indian researchers stand to benefit from studying the geologically young and unique Chang’e 5 samples as well by publishing varied and more current work. Notably, doing so would also naturally open windows for the national scientific community to access Chang’e 6 samples in the future, which are even more diverse and valuable.

Even more crucially perhaps, going through the logistical process of proposing Chang’e sample studies and then getting & storing them would provide India with a good programmatic sense of the kinds of things that it would also need to do to share Chandrayaan 4 samples when our time comes. This experience would span an obviously indirect yet nuanced sense of China’s storage facilities, initial characterization and cataloging of samples, their transport systems, and so on. Sure, India could also pick up things from how NASA manages Apollo samples but that system is utterly expensive, having been made in a different era of budgetary freedom during the Cold War. In contrast, the scale and scope of China’s lunar sample facilities are more in reach for India to replicate. And they are modern too. There’s no harm in seeking inspiration from the only other facility on Earth that concerns the same celestial body and is also closest in scope to what India desires for Chandrayaan 4. I hope Indian research proposals make their way into the second round of international Chang’e 5 sample studies.

While geopolitical hesitation may keep this prospect a dream, it’s worth noting that in the meanwhile China did formally welcome India to cooperate on Moon missions and the Sino-led ILRS Moonbase project this past May. The invitation came from none other than Wu Weiren, the Chief Designer of China’s extremely successful lunar program.

In fact, Indian scientists applying for Chang’e sample studies can be an enabler of even more valuable scientific exchanges with the Chinese. One of these could be a literal sample exchange, a mechanism known to work very well in the past and present worldwide—such as the recent asteroid sample swap between the US and Japan. With Chandrayaan 4 lunar samples in hand, ISRO should initiate a sample exchange program with China and the US, swapping Chang’e and Artemis samples respectively for the also uniquely valuable Chandrayaan 4 Moon materials. With this program, all three nations will benefit in terms of their scientific outputs while India also gets better geopolitical leverage and China further improves its international relations. A win-win for all, and for humanity.

Indian and Chinese space researchers have an opportunity to interact, exchange ideas, and consider future collaborations at the International Lunar Sample Research Symposium being hosted by the University of Hong Kong this November. I sincerely hope that ISRO is sending, or is at least considering sending, some of its researchers to this science-focused symposium for mutual benefit.

In turn, realizing such proposed collaborations and building trust in the process could be the start of many more synergies between India and China at the Moon.

On our Moon
from where the Sun never shines,
a new era will dawn.
– Jatan