ISRO to Perform Lunar Sample Return

On the 23rd of August 2023 the Indian Space Research Organization successfully landed Chandrayaan-3 on the lunar South Pole. This major accomplishment made India the fourth country to successfully land on the Moon, and the first to land at the greatly-coveted lunar South Pole. The surface mission, which only lasted ten days, has long since ended, as have attempts to reawaken the lander, but India’s lunar ambitions have not ended. In a lecture given at the Indian Institute of Tropical Meteorology Foundation Day on November 17th, Shri Nilesh M. Desai, director of India’s Space Application Center, outlined India’s next missions to the Moon – including the ambitious and tantalizing official plan for Chandrayaan-4.

In previous reporting, Space Scout indicated that Chandrayaan-4 referred to LuPEx, a Japanese-Indian joint mission; the lecture given at IITM Foundation Day makes it clear this is no longer the case. Chandrayaan-4 now unambiguously refers to the next entirely Indian mission to the Moon, the international LuPEx mission is separate. 

According to Shri Nilesh M. Desai; after the success of Chandrayaan-3, the Indian Prime Minister, Narendra Modi, encouraged ISRO to pursue an even greater challenge for the next mission, and they certainly have. Chandrayaan-4 has been announced as a sample return mission, and is planned to occur by 2028. Sample return missions, both to the Moon and beyond, are considered some of the most complex and high risk robotic missions that can be attempted, but should they succeed, sample returns can be by far the most valuable. Chandrayaan-4 is no different, in both respects. Chandrayaan-4 consists of four modules, an Ascent Module (AM), a Descent Module (DM), a Transfer Module (TM), and a Return Module (RM). These modules are divided across two spacecraft, the AM and DM constituting one spacecraft, and the RM and TM making up the other.

The mission will begin with the launch of the respective launches of the TM+RM aboard a GSLV Mark 2 rocket, and the AM+DM aboard a LVM3 rocket. The TM+RM spacecraft will be left on a geostationary transfer orbit, and make the rest of the journey to the Moon under its own power, meanwhile the AM+DM spacecraft will be launched on a direct lunar transfer. Once it arrives in Lunar orbit, the TM+RM spacecraft will stand by while the AM+DM performs its landing on the lunar surface. Under the power of the descent module, the robotic lander will descend to a familiar point on the lunar surface–Shiv Shakti Point–the landing site of Chandrayaan-3. This would mark the first time since Apollo 12 that a mission to the lunar surface landed in proximity to a previous mission, adding another ambitious achievement to an already staggering mission plan.

One may ask why ISRO intends to collect samples from Shiv Shakti Point, as opposed to exploring a new region of the surface. To answer this question, a quick recap of the operations conducted by Chandrayaan-3 proves helpful. While descending to its landing site, Chandrayaan-3 captured a massive collection of imagery, meaning the site is already well mapped, ahead of a prospective return. During their ten day mission on the lunar surface, the lander Vikram and rover Pragyan were able to perform the first in-situ measurements of surface conditions and properties of the lunar South Pole. While ice was not detected directly, a thermal experiment demonstrated the lunar regolith acts as a strong insulator, proving the South Pole could host ice deposits. The rover, Praygan, detected a variety of elements using its on-board laser spectrometer, including the first detection of sulfur from the lunar surface. Sulfur is a strong clue into the Moon’s volcanic history, and while sulfur has been observed from orbit of the Moon since the 1970s, the measurements from Pragyan are far more definitive. Most significantly, the experiment further revealed that sulfur on the Moon is not found embedded within another material, but on its own. In an interview with the BBC, Mila Mitra, a former NASA scientist, explained the finding “indicates the presence of water ice on the lunar surface and since sulfur is a good fertilizer, it’s good news as it can help grow plants if there’s habitat on the Moon.”

On the surface, the DM+AM vehicle will use a robotic arm mounted on the DM to acquire samples of the lunar regolith and transfer those samples onto the AM. After the samples are secured, the AM will detach from the DM and launch itself into lunar orbit under its own power. Once in space, the AM will move to rendezvous and dock with the TM+RM spacecraft. Following the docking, the mission will employ a second robotic arm, this time mounted on the Transfer Module, to move the lunar samples from the AM and into the RM. The Ascent Module is then discarded, and the TM+RM returns to Earth-centric orbit, where the Return Module is then jettisoned for return to Earth. While the designs for these spacecraft were not shown, only the mission outline, the Return Module will likely be an aeroshell much like those seen on other sample return missions, and make the final descent to Earth’s surface under parachutes.

While Chandrayaan-4 is doubtless in its early days as a mission, the simple declaration of its intention and purpose shows the remarkable ambition we have come to expect from ISRO. The Indian space agency has had an incredible year, which has seen the landing of Chandrayaan-3, the launch of the Aditya-L1 coronagraphy mission (set to arrive at the Earth-Sun L1 point in January), and a successful first launch escape system test for its upcoming Gaganyaan crew vehicle. India’s next lunar operations will be the assembly, provision, and operation of the landing vehicle for the joint Indian-Japanese LuPEx mission, which will see a Japanese rover delivered in the vicinity of the exact South Pole of the Moon. LuPEx, and potentially Chandrayaan-4, will take advantage of precision landing technology being demonstrated by JAXA’s SLIM mission, currently in flight and expected to arrive at the Moon in late December. Also in December, Vulcan’s inaugural launch will mark the start of NASA’s CLPS program, which will have as many as five launches next year, including NASA’s VIPER rover.

All of this, including the previously mentioned Chang’e 6 mission, is set to occur in the next twelve months, with Artemis II, the first human crew to fly past the Moon since Apollo 17, not long after. Truly, we have entered a modern, and notably international, golden age of lunar exploration.

Edited by Nik Alexander