Chandrayaan-4 (/ˌtʃʌndrəˈjɑːn/ CHUN-drə-YAHN) is a planned lunar sample-return mission and the fourth mission in the Chandrayaan programme, a series of lunar-exploration missions developed by the Indian Space Research Organisation (ISRO).^[1][2] The mission is currently under conceptualisation phase and is slated for launch no earlier than 2028.^[3]

History

On 17 November 2023, the plan for a lunar sample return mission was revealed by Nilesh M. Desai, director of the Space Applications Centre (SAC) during the 62nd foundation day ceremony of the Indian Institute of Tropical Meteorology (IITM) in Pune. He said that it is a very ambitious mission and hopefully in next five to seven years we would be able to meet this challenge of bringing samples from the surface of the Moon.^[7][8] After the launch of INSAT-3DS, a top official said that the agency has been working internally on a plan for the launch of this mission and is involved in developing a 'novel design' and 'high-end technology' in this connection. Chairman S. Somanath stated the insufficiency with the current rocket capabilities as a reason for opting for a novel design and the secretary of the Department of Space said that the mission plan along with the cost estimate has to be approved by the government before he can have a final word.^[9][10]

Precursor experiments on Chandrayaan-3

On 4 September 2023, the Vikram lander of Chandrayaan-3 fired its engines for a brief 'hop' on the lunar surface, ascending 40 cm off the lunar surface and translating a similar distance laterally across the surface.^[11] The instruments and rover deployment ramp were retracted for the hop and redeployed afterwards. The test demonstrated capabilities to be used in potential future sample return missions.^[12][13][14]

• Video footage of hop
• 
  PM detour

After one month of operation, it was decided to so utilise over 100 kg of fuel left in the propulsion module of Chandrayaan-3 as to perform a series of Earth return operations to derive additional information for future lunar missions and to determine strategies for sample return missions. The first lunar bound apogee raising manoeuvre was executed on 9 October 2023 raising the apogee to 5112 km. This was followed by the crucial Trans-Earth Injection (TEI) and four lunar flybys with the last flyby on 7 November 2023. The module exited lunar SOI on 10 November 2023 and had the first Earth bound perigee crossing on 22 November 2023 at an altitude of about 154,000 km.^[15]

Objectives

The aim of the mission is to collect samples from the lunar surface and return them safely back to Earth for scientific studies. In fulfilment of this aim, the mission's objectives are to perform:^[6]

1. A safe and soft landing on the lunar surface.
2. Lunar sample collection and containerisation.
3. Ascent from the Moon's surface.
4. Docking and undocking in lunar orbit.
5. Transfer of samples from one module to another.
6. Return and re-entry to Earth for sample delivery.

Spacecraft

Chandrayaan-4^[5][6]

Composite 1		Composite 2
PSLV / GSLV	Rocket		LVM3
Re-entry Module	Module 1		Ascender Module
Transfer Module	Module 2		Descender Module
—	Module 3		Propulsion Module

Note: Final rendering of the spacecraft may vary as mission is still under conceptualisation. This will also be the first mission involving two launch vehicles to complete a lunar sample-recovery mission.

Mission Components

• Lunar Propulsion module - It is similar to the propulsion module on Chandrayaan-3. It will ferry the combined Lunar lander and ascender stage to the moon.^[16][17]

• Lunar lander will land on the Moon with instrumentation. It supports the ascend stage along with the soil sampling instrumentation.^[18][16][17]

• Lunar module ascender Once the samples from the Moon are collected and stored, the ascender module will eject from the lander and would launch from the Moon, using the lander as a launch pad and enter low-lunar orbit.^[18][16][17]

• Transfer module will collect the samples from the ascend stage, transfer them to the reentry module, fire its engine to set both itself and the re-entry module towards Earth, release the payload, and loop back around the Earth.^[18][16][17]

• Reentry module will hold the sample from lunar orbit. It is designed to survive atmospheric reentry and land with the lunar regoliths.^[18][16][17]

Mission profile

The mission incorporates dual launches. The Propulsion-Descender-Ascender Composite will be launched over an LVM3 and among which the Descender Module with the Ascender Module attached intact to its top will make a descent to the predesignated landing site on lunar surface. The Transfer-Re-entry Composite launched over a PSLV or GSLV will be intactly parked into a suitable lower lunar orbit.^[6] ISRO is yet to determine the sequence of the launches.^[19][17][16]

The Descender Module will collect the lunar samples via robotic arm mechanism and transfers onto the Ascender Module. This is followed by the Ascender Module separating and ascenting to the lunar orbit for docking with the Transfer Module. This will form a Ascender-Transfer-Re-entry Composite on lunar orbit. The Transfer Module will transfer the collected lunar samples from Ascender Module to the Re-entry Module and this is followed by the Ascender Module separation from the tri-module structure. The Transfer-Re-entry Composite will make a return operation to Earth orbit. The Re-entry Module will separate from the Transfer Module on a suitable Earth bound orbit and make its re-entry for touchdown on Earth.^[20][5][6]

SPADEX

The Ascender Module-Transfer Module docking in lunar orbit requires that the prescheduled technology demonstrator mission Space Docking Experiment (SPADEX) be completed. It is a twin spacecraft mission being developed by the ISRO to develop technologies related to orbital rendezvous, docking and formation flying.^[21] It will launch on a PSLV rocket in the last quater of 2024.