ISRO’s Chandrayaan-3 mission a success

Chandrayaan-3 is the third Indian lunar exploration mission under the Indian Space Research Organisation’s (ISRO) Chandrayaan programme. It consists of a lander named Vikram and a rover named Pragyan, similar to those of the Chandrayaan-2 mission. The propulsion module carried the lander and rover configuration to lunar orbit in preparation for a powered descent by the lander.

Chandrayaan-3 was launched on 14 July 2023 with the mission objectives of getting the lander to land safely and softly on the surface of the Moon, observing and demonstrating the rover's driving capabilities on the Moon, and then conducting and observing experiments on the materials available on the lunar surface to better understand the composition of the Moon. The spacecraft entered lunar orbit on 5 August, and the lander touched down in the lunar South Pole region on 23 August 2023 at 12:32 UTC, making India the fourth country to successfully land on the lunar surface, and the first to do so near the lunar South Pole.

The lunar South Pole region holds particular interest for scientific exploration due to studies that show large amounts of ice there. Mountainous terrain and unpredictable lighting conditions not only protect the ice from melting but also make landing scientific probes there a challenging undertaking. This ice could contain solid state compounds that would normally melt under warmer conditions elsewhere on the Moon, compounds which could provide insight into lunar, Earth and Solar System history. Ice could also be used as a source of drinking water and hydrogen for fuel and oxygen for future crewed missions and outposts.

The European Space Tracking network (ESTRACK), operated by the European Space Agency (ESA), and Deep Space Network operated by Jet Propulsion Laboratory (JPL) of NASA are supporting the mission. For the Chandrayaan-3 mission, ESA is coordinating routine support from its Kourou station in French Guiana and from Goonhilly Earth Station Ltd in the UK. These stations compliment support from NASA’s Deep Space Network and ISRO’s own stations. ESA’s 35-metre antenna in New Norcia, Australia, provided additional tracking support during the lunar landing, serving as a backup for ISRO’s own ground station. New Norcia received the stream of vital signs from the Chandrayaan-3 lander, information about its health, location and trajectory, in parallel with the ISRO station. This type of back-up support is common during key moments of a space mission such as a landing.

It was this stream of telemetry that was ultimately used to confirm the success of the landing. Under a new cross-support arrangement, ESA tracking support could be provided for upcoming ISRO missions such as those of India's first human spaceflight programme, Gaganyaan, and the Aditya-L1 solar research mission. In return, future ESA missions will receive similar support from ISRO's own tracking stations.

Chandrayaan-3 comprises three main components: a propulsion module, lander, and rover. The 2,148 kg propulsion module carries the lander and rover configuration to a 100 kilometres lunar orbit. It is a box-like structure with a large solar panel mounted on one side and a cylindrical mounting structure for the lander (the Intermodular Adapter Cone) on top. The propulsion module carries Spectro-polarimetry of Habitable Planet Earth (SHAPE) to study spectral and polarimetric measurements of Earth from the lunar orbit in the Near Infrared (NIR) wavelength range (1–1.7 μm [3.9×10−5–6.7×10−5 in]).

The 1,752 kg Vikram lander is programmed for the soft landing on the Moon. It is also box-shaped, with four landing legs and four landing thrusters capable of producing 800-Newtons of thrust each. It carries the rover and various scientific instruments to perform on-site analysis. The lander for Chandrayaan-3 has four variable-thrust engines with slew rate changing capabilities, unlike Chandrayaan-2's lander, which had five, with the fifth one being centrally mounted and capable only of fixed thrust. 

The 26 kg Pragyan rover is a six-wheeled vehicle with a mass of 26 kgs. It is 917  millimetres x 750 millimetres x 397 millimetres in size. The rover has undertaken multiple measurements to support research into the composition of the lunar surface, the presence of water ice in the lunar soil, the history of lunar impacts, and the evolution of the Moon's atmosphere. Payloads include an Alpha Particle X-ray Spectrometer (APXS) to determine the elemental composition (Mg, Al, Si, K, Ca, Ti, Fe) of lunar soil and rocks around the lunar landing site, and Laser Induced Breakdown Spectroscopy (LIBS) to derive the chemical composition and infer the mineralogical composition of the lunar surface.

Chandrayaan-3 was launched aboard an LVM3-M4 rocket on 14 July 2023, at 09:05 UTC from Satish Dhawan Space Centre Second Launch Pad in Sriharikota, Andhra Pradesh, India, entering an Earth parking orbit with a perigee of 170-km and an apogee of 36,500-km.

After a series of earth bound manoeuvres that placed Chandrayaan-3 in a trans-lunar injection orbit, ISRO performed a Lunar-Orbit Insertion (LOI) on 5 August, successfully placing the Chandrayaan-3 spacecraft into an orbit around the Moon. The LOI operation was carried out from the ISRO Telemetry, Tracking & Command Network (ISTRAC) in Bengaluru. On 17 August, the Vikram lander separated from the propulsion module to begin the last phase of the mission.

Since reaching the moon's South Pole, Chandrayaan-3 deployed the Pragyan rover to explore the cratered surface, harnessed integrated cameras to send back videos of its environment, and even started working on the research objectives planned. The first video of the rover, posted on 25 August 2023, showed it leaving the Vikram lander on a ramp and driving onto the Moon. ISRO posted the video in a thread on X that also included footage from the lander approaching its landing site and kicking up dust as it touched down on the surface. ISRO wrote afterwards that the rover’s two scientific instruments had been turned on and that it had moved eight meters. On 26 August, ISRO posted a new video, shot from the lander, of the rover's drive away, moving almost out of the lander’s sight. On 27 August, it published two pictures after the rover encountered a large crater positioned 3 metres ahead of its location. However, the rover safely headed on a new path afterwards.

ISRO also released a first-of-its-kind data from the observations made by ChaSTE (Chandra's Surface Thermophysical Experiment), one of the four instruments present on the lander module. ChaSTE was meant to study the heat conductivity of the Moon’s surface and measure the differences in temperatures at different points on and below the surface, with the overall objective of creating a thermal profile of the Moon.

The first set of data released by ISRO showed a very sharp difference in temperatures just above and below the surface of the Moon. A graphical plot put out by ISRO showed that while temperatures on the surface were over 50C (122F), they dropped to nearly −10C (14F) just a few millimetres below the surface. The measurements suggested that the topsoil of the lunar surface did not conduct heat very well, and insulated the sub-surface from heat. These measurements were consistent with what is known about the thermal profile of the Moon from previous expeditions and experiments.

On 29 August, ISRO said that the Laser-Induced Breakdown Spectroscope (LIBS) instrument onboard the Pragyan rover has "unambiguously" confirmed the presence of sulphur in the lunar surface near south pole. The presence of sulphur on the Moon has been known before; however, it was detected for the first time at the South Pole. Additionally, there was no previous direct evidence of the element.

Congratulating the ISRO team behind the successful Chandrayaan-3 Moon Mission at ISRO Telemetry, Tracking and Command Network in Bengaluru, Prime Minister Narendra Modi announced that the touchdown point of the Vikram lander would henceforth be known as Shiv Shakti point. He further declared 23 August, the day the Vikram lander landed on the moon, as National Space Day.

Article by Sayan Majumdar

All photos: ISRO

Text: Sayan Majumdar

Photos: ISRO