Chandrayaan-3: India's Third Lunar Mission

Chandrayaan-3: India's Third Lunar Mission

Chandrayaan-3 is the third mission in the Chandrayaan programme, a series of lunar-exploration missions developed by the Indian Space Research Organisation (ISRO). Launched on 14 July 2023, the mission consists of a lunar lander named Vikram and a lunar rover named Pragyan, similar to those launched aboard Chandrayaan-2 in 2019. Chandrayaan-3 was launched from Satish Dhawan Space Centre on 14 July 2023. The spacecraft entered lunar orbit on 5 August, and the lander touched down near the Lunar south pole on 23 August at 18:03 IST (12:33 UTC), making India the fourth country to successfully land on the Moon, and the first to do so near the lunar south pole. On 3 September the lander hopped and repositioned itself 30–40 cm (12–16 in) from its landing site. The Vikram lander and Pragyan rover were set to sleep on 2 September and 4 September respectively due to depleting solar power with sunset at the landing site. The lander and rover are planned to start working again at local sunrise on September 22.

## Mission Objectives

The main objectives of Chandrayaan-3 are to demonstrate India's capability to soft-land on the lunar surface and operate a robotic rover, to explore the lunar south pole region, and to conduct scientific experiments using the instruments onboard the lander and rover. The mission also aims to study the lunar topography, mineralogy, elemental abundance, lunar exosphere, and signatures of hydroxyl and water ice.

## Mission Design

Chandrayaan-3 consists of two modules: a propulsion module and a lander module. The propulsion module carries the lander from launch injection to lunar orbit. The lander module houses the rover inside it. The total mass of the spacecraft is 3900 kg, of which 2148 kg is the propulsion module, 1726 kg is the lander module, and 26 kg is the rover.

The propulsion module is powered by a bi-propellant propulsion system (MMH + MON3) with four thrusters of 800 N each and eight thrusters of 58 N each. It also carries a scientific payload called SHAPE (Spectro-polarimetry of HAbitable Planet Earth), which aims to measure the polarization of Earth's reflected light as seen from lunar orbit.

The lander module is named Vikram, after Vikram Sarabhai, the father of the Indian space programme. It has four legs and a ramp for the rover to descend. It is equipped with a bi-propellant propulsion system (MMH + MON3) with four throttleable engines of 800 N each for landing. It also has various sensors and cameras for navigation, hazard detection, and landing site selection. It carries four scientific payloads: RAMBHA (Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere), ChaSTE (Chandra’s Surface Thermo physical Experiment), ILSA (Instrument for Lunar Seismic Activity), and LRA (Laser Retroreflector Array).

The rover module is named Pragyan, which means wisdom in Sanskrit. It has six wheels and can travel up to 500 m from the lander. It is powered by solar energy and can communicate with the lander only. It carries two scientific payloads: APXS (Alpha Particle X-Ray Spectrometer) and LIBS (Laser Induced Breakdown Spectroscope).

## Mission Highlights

Chandrayaan-3 was launched on 14 July 2023 at 14:35:17 IST (09:05:17 UTC) by a Launch Vehicle Mark-3 (LVM3) rocket from Satish Dhawan Space Centre in Sriharikota. The launch was successful and placed Chandrayaan-3 into an Earth parking orbit of 170 km x 39000 km.

After five orbit-raising manoeuvres around Earth, Chandrayaan-3 performed a trans-lunar injection on 29 July 2023, which boosted its velocity to escape Earth's gravity and head towards the Moon. After travelling for about six days, Chandrayaan-3 entered lunar orbit on 5 August 2023 by firing its main engine for about 30 minutes.

Chandrayaan-3 then performed four orbit-lowering manoeuvres around the Moon to reach an orbit of 153 km x 163 km. On 20 August 2023, Chandrayaan-3 separated its lander module from its propulsion module. The propulsion module remained in orbit as an orbital platform for future missions.

The lander module then performed two de-orbit manoeuvres to lower its orbit to an altitude of about 35 km above the lunar surface. On 23 August 2023, the lander module initiated its powered descent phase, which lasted for about 15 minutes. During this phase, the lander used its sensors and cameras to identify a safe and flat landing site near the lunar south pole. The lander then fired its engines to reduce its speed and altitude, and finally touched down softly on the lunar surface at 18:03 IST (12:33 UTC).

The landing site of Chandrayaan-3 is called Shiv Shakti point, located at 69.373°S 32.319°E, between Manzinus C and Simpelius N craters. This site was chosen because it is close to the lunar south pole, where there is a possibility of finding water ice and other resources. The site also has a long duration of sunlight, which is beneficial for the solar-powered lander and rover.

After landing, the lander deployed its ramp and released the rover. The rover then rolled down the ramp and started exploring the lunar terrain around the lander. The rover can travel up to 100 m from the lander and can perform in-situ analysis of the lunar soil using its instruments.

The lander and rover have a mission life of one lunar day, which is equivalent to about 14 Earth days. They are designed to operate during the day and hibernate during the night, when the temperature drops to below -150 °C. The lander and rover can communicate with each other using radio links, and with Earth using the Indian Deep Space Network (IDSN) antennas located in Byalalu, near Bangalore.

The lander and rover have performed various scientific experiments and measurements during their mission. They have collected data on the lunar surface temperature, seismic activity, plasma density, surface composition, elemental abundance, and water ice signatures. They have also sent back high-resolution images and videos of the landing site and its surroundings.

On 2 September 2023, the lander entered its sleep mode as the local sunset approached. On 4 September 2023, the rover also entered its sleep mode after completing its exploration activities. The lander and rover are expected to wake up again on 22 September 2023, when the local sunrise occurs. ISRO will attempt to re-establish communication with them and resume their operations.

Chandrayaan-3 is a milestone achievement for India's space programme, as it demonstrates India's capability to soft-land on the Moon and operate a robotic rover. It also enhances India's scientific knowledge of the Moon, especially its south pole region, which holds great potential for future exploration and utilization. Chandrayaan-3 is a proud moment for all Indians and a tribute to Vikram Sarabhai's vision of using space technology for national development.