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[8] 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.[9][note 1] On 3 September the lander hopped and repositioned itself 30–40 cm (12–16 in) from its landing site.[13]
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.[14][15]
On 22 July 2019, ISRO launched Chandrayaan-2 on board a Launch Vehicle Mark-3 (LVM3)launch vehicle consisting of an orbiter, a lander and a rover.[16] The lander was scheduled to touch down on the lunar surface on 6 September 2019 to deploy the Pragyan rover. The lander lost contact with mission control, deviated from its intended trajectory while attempting to land near the lunar south pole, and crashed.[17][18]
The lunar south pole region holds particular interest for scientific exploration. Studies show large amounts of ice there. Mountainous terrain and unpredictable lighting protect the ice from melting, but they also make landing scientific probes there a challenging undertaking. The 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. For future crewed missions and outposts, ice could also be a source of drinking water and of hydrogen for fuel and oxygen.[19][20]
ISRO's mission objectives for the Chandrayaan-3 mission are:
Engineering and implementing a lander to land safely and softly on the surface of the Moon.
Observing and demonstrating the rover's driving capabilities on the Moon.
Conducting and observing experiments on the materials available on the lunar surface to better understand the composition of the Moon.[23]
Spacecraft
Design
Chandrayaan-3 comprises three main components: a propulsion module, lander, and rover.
Chandrayaan-3 encapsulated within LVM3's payload fairing
Chandrayaan-3 integrated components
Propulsion module
The propulsion module carried the lander and rover configuration to a 100-kilometre (62 mi) lunar orbit. It was 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.[24][25]
Propulsion module
Lander
The Vikram lander was responsible 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 carried the rover and has various scientific instruments to perform on-site analysis.[26][27] The lander 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. One of the main reasons for Chandrayaan-2's landing failure was attitude increase during the camera coasting phase. This was removed by allowing the lander to control attitude and thrust during all phases of descent. Attitude correction rate was increased from Chandrayaan-2's 10°/s to 25°/s with Chandrayaan-3. Additionally, the Chandrayaan-3 lander is equipped with a laser Doppler velocimeter (LDV) to allow measuring attitude in three directions.[28][29] The impact legs were made stronger compared to Chandrayaan-2 and instrumentation redundancy was improved. It targeted a more precise 16 km2 (6.2 sq mi) landing region based on images provided by the Orbiter High-Resolution Camera (OHRC) onboard Chandrayaan-2's orbiter. ISRO improved the structural rigidity, increased polling in instruments, increased data frequency and transmission, and added additional multiple contingency systems to improve lander survivability in the event of failure during descent and landing.[30][29]
Lander
Rover
The Pragyan rover is a six-wheeled vehicle with a mass of 26 kilograms (57 pounds). It is 917 by 750 by 397 millimetres (36.1 in × 29.5 in × 15.6 in) in size.[31] The rover is expected to take 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.[32][8]
Spectro-polarimetry of Habitable Planet Earth (SHAPE) will study spectral and polarimetric measurements of Earth from the lunar orbit in the near-infrared (NIR) wavelength range (1–1.7 μm).[24][25]
Spectro-polarimetry of Habitable Planet Earth (SHAPE)
On 17 August, the Vikram lander separated from the propulsion module to begin the last phase of the mission.[39]
Landing
On 23 August 2023, as the lander approached the low point of its orbit, its four engines fired as a braking manoeuvre at 30 kilometres (19 mi) above the Moon's surface. After 11.5 minutes, the lander was 7.2 km (4.5 miles) above the surface; it maintained this altitude for about 10 seconds, then stabilized itself using eight smaller thrusters and rotated from a horizontal to a vertical position while continuing its descent.
It then used two of its four engines to slow its descent to roughly 150 metres (490 ft); it hovered there for about 30 seconds and located an optimal landing spot before continuing downward and touching down at 12:33 UTC.[26][40]
The Moon photographed by the Lander Position Detection Camera (LPDC) aboard Chandrayaan-3 lander on 15 August 2023
View from the Lander Imager Camera-1 (LI-1) on 17 August 2023 just after the separation of the Chandrayaan-3 Lander Module from the Propulsion Module
Chandrayaan-3 orbital manoeuvre
Surface operations
After landing near the Moon's south pole region, Chandrayaan-3's Vikram lander deployed the Pragyan rover to explore the cratered surface, using integrated cameras to send back videos of its environment, and started working on the research objectives planned for a two-week stay on the Moon.[55]
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's surface. ISRO also shared video footage from the lander as it approached the landing site, 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.[56]
On 26 August, ISRO posted a new video of the rover driving away, moving almost out of the lander's sight.[57] On 27 August, ISRO published two pictures taken by the rover three metres (9.8 ft) from the edge of a large crater.[58]
On 3 September, the rover was put into sleep mode after it had completed all of its assignments. Its batteries were charged and receiver left on, according to ISRO, in preparation for the impending lunar night.[59] "The rover's payloads are turned off and the data it collected has been transmitted to Earth via the lander", the statement said. Chandrayaan-3's lander and rover were expected to operate only for one lunar daylight period, or 14 Earth days, and the on-board electronics were not designed to withstand the −120 °C (−184 °F) nighttime temperatures on the Moon.[60] If the rover and lander were to survive the lunar night, the mission is planned to be extended for further science operations.
Vikram fired its engines for a brief 'hop' on the lunar surface on 3 September, ascending 40 cm (16 in) off the lunar surface and translating a similar distance laterally across the surface. The test demonstrated capabilities to be used in potential future sample return missions. The instruments and rover deployment ramp were retracted for the hop and redeployed afterwards.[61][62][63]
Mission life
Propulsion module: Carries lander and rover to 100-by-100-kilometre (62 mi × 62 mi) orbit, with operation of experimental payload for up to six months.[64]
Lander module: one lunar daylight period (14 Earth days)[64]
Rover module: one lunar daylight period (14 Earth days).[64]
In December 2019, ISRO requested the initial funding of the project, amounting to ₹75 crore (US$9.4 million), out of which ₹60 crore (US$7.5 million) would be for meeting expenditure towards machinery, equipment, and other capital expenditure, while the remaining ₹15 crore (US$1.9 million) was sought for operating expenditure.[71] Amit Sharma, CEO of an ISRO vendor, said, "With local sourcing of equipment and design elements, we are able to reduce the price considerably."[72]
Confirming the existence of the project, ISRO's former chairman K. Sivan stated that the estimated cost would be around ₹615 crore (equivalent to ₹721 crore or US$90 million in 2023).[73][74][75]
Results
The Associated Press, while commenting on the success of the mission, said, "The successful mission showcases India's rising standing as a technology and space powerhouse and dovetails with Prime Minister Narendra Modi's desire to project an image of an ascendant country asserting its place among the global elite."[76]
Temperature variation
ISRO also released data from the observations made by ChaSTE (Chandra's Surface Thermophysical Experiment), one of the four instruments present on the lander module. ChaSTE was designed 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 50 °C (122 °F), they dropped to nearly −10 °C (14 °F) 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.[77][77]
These measurements were consistent with what is known about the thermal profile of the Moon from previous expeditions and experiments. But this was the first direct measurement of temperatures of the topsoil and the subsoil near the south pole.[78]
ISRO scientist BH Darukesha said the high range of 70-degree-Celsius (158-degree-Fahrenheit) temperature near the surface was "not expected".[79]
Detection of sulfur
On 29 August, ISRO reported that the laser-induced breakdown spectroscope (LIBS) instrument onboard the Pragyan rover has "unambiguously" confirmed the presence of sulfur in the lunar surface near the south pole, through "first-ever in-situ measurements".[80][81] The presence of sulfur on the Moon has been known before;[82] however, it was detected for the first time at the south pole by the rover.[83]
Noah Petro, a project scientist at NASA, while speaking to the BBC, stated that while sulfur has been known to be in the lunar regolith from Apollo program samples, he described Pragyan's findings as a "tremendous accomplishment".[84]
Apart from sulfur, the rover also detected other elements including aluminium (Al), calcium (Ca), iron (Fe), chromium (Cr), titanium (Ti), manganese (Mn), silicon (Si), and oxygen (O).[85] The agency said the search for hydrogen (H) is also underway.[86][77]
Plasma measurement
On 31 August, ISRO released plasma density data from the RAMBHA Instrument aboard the Vikram lander. Initial assessments reported relatively low plasma densities above the lunar surface varying from 5 to 30 million electrons per m3. The evaluation pertains to early stages of the lunar day. The probe aims to explore the changes in the near-surface plasma environment throughout the duration of the lunar day.[87]
Seismic measurements
On the same day, ISRO released data from the ILSA payload on the lander, providing vibration measurements of the rover movement on 25 August, and a presumed natural event on 26 August. The cause of the latter event is a subject of investigation,[88] it is suspected to be a moonquake.[77]
Lunar water
John Bridges, a professor of planetary science at the University of Leicester, UK,[89] told New Scientist that due to the low pressure on the Moon it would be "unlikely" for Chandrayaan-3 to find liquid water near to the surface – even in areas where the temperature was above freezing point so water would not be trapped in ice – because it would boil away, although at lower depths the pressure could rise enough to allow liquid water. However, he also added that it's "too early" to interpret the readings from Chandrayaan-3. "But it's fantastic they're getting data", Bridges said. "You can't help comparing it to certain other space agencies; engineers are just getting on now and doing it. They're sort of overtaking Russia", he concluded.[90]
Domestic reactions
Congratulating the ISRO team behind the successful Chandrayaan-3 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.[91] He further declared 23 August, the day the Vikram lander landed on the Moon, as National Space Day.[92][93]
ISRO chief S. Somanath exclaimed "India is on the Moon" after Chandrayaan-3 successfully touched down on the surface of the Moon.[94] "We learnt a lot from our failure and corrected it. It's now 14 days of work and we have to conduct experiments," he told India Today.[95]
P Veeramuthuvel, the Project Director of the mission said, "It's a great moment of happiness. On behalf of the team it gives me immense satisfaction on achieving this goal as the Project Director of the mission. The entire mission operations right from launch till landing happened flawlessly as per the timeline".[96] S. Mohana Kumar, the Mission Director said that Chandrayaan-3 was a 'team effort', and that the equipment suppliers played a key in achieving the milestone by delivering the mission critical consignments in a timely manner.[97]
Meanwhile, former ISRO chief K Sivan, under whose tenure the Chandrayaan-2 was launched said, "We are really excited to see this grand success. For this, we have been waiting for the last four years. This success is sweet news for us and for the entire nation."[98]
DY Chandrachud, the Chief Justice of India hailed the landing as a "historic achievement" and congratulated ISRO on the feat. "It is with immense pride as a citizen of our great nation that I witnessed the remarkable landing of Chandrayaan-3 on the Moon today," he said. "It is all the more significant because India is the only nation to have achieved the lunar landing on the south pole of the Moon. This will help new avenues and scientific research and discovery. Truly, this lunar landing represents a milestone in the onward march of our nation," he added.[99]
^Vaniman, D.; Pettit, D.; Heiken, G. (1992). "Uses of lunar sulfur". Lunar Bases and Space Activities of the 21st Century. SAO/NASA Astrophysics Data System (ADS): 429. Bibcode:1992lbsa.conf..429V. Archived from the original on 30 August 2023. Retrieved 30 August 2023.
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Cubesats are smaller. Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
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