Chandrayaan-3

• 1. The Crash That Changed Everything

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  On the 23rd of August 2023, a box-shaped lander named Vikram touched down near the lunar south pole at 18:04 IST. This moment marked India's first soft landing on another celestial body and made ISRO the fourth national space agency to achieve this feat. The success stood in stark contrast to the failure of Chandrayaan-2 just four years prior. On the 6th of September 2019, that earlier lander lost contact with mission control during its descent. It deviated from its intended trajectory and crashed into the lunar surface instead of deploying its Pragyan rover.

  The crash forced Indian engineers to rethink their entire approach to lunar landing systems. They studied every data point from the 2019 failure to identify exactly where things went wrong. The fifth engine on the Chandrayaan-2 lander was centrally mounted and capable only of fixed thrust. This design choice contributed to an altitude increase during the camera coasting phase that led to the crash. Engineers removed that central engine from the new design entirely.

  Chandrayaan-3 introduced variable-thrust engines with slew rate changing capabilities. The team increased the altitude correction rate from 10 degrees per second to 25 degrees per second. They added a laser Doppler velocimeter to measure altitude in three directions simultaneously. Impact legs were strengthened and instrumentation redundancy improved significantly. These changes targeted a more precise landing region based on images provided by the Orbiter High-Resolution Camera onboard Chandrayaan-2's orbiter.

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• 2. Engineering A New Descent System

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  The Vikram lander carried four landing thrusters capable of producing 800 newtons of thrust each. During the final descent on the 23rd of August, these four engines fired as a braking maneuver at approximately 7 kilometers above the Moon's surface. After 11.5 minutes, the lander maintained this altitude for about 10 seconds before stabilizing itself using eight smaller thrusters.

  Engineers rotated the vehicle 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 40 meters per second. The lander hovered there for about 30 seconds and located an optimal landing spot before continuing downward. This careful sequence prevented the altitude increase that had doomed the previous attempt.

  ISRO improved structural rigidity throughout the lander design. They increased polling frequency in instruments and boosted data transmission rates. Multiple contingency systems were added to improve survivability during any failure phase. The lander was not built to withstand the cold temperatures of the lunar night, so it shut down at sunset over the landing site twelve days after touchdown. This limitation reduced their maximum lifespan to 14 Earth days or one lunar day.

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• 3. Six Wheels On A Rocky Surface

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  The Pragyan rover is a six-wheeled vehicle with a mass of approximately 26 kilograms. It measures roughly 75 centimeters by 75 centimeters in size. The rover took multiple measurements to support research into the composition of the lunar surface and the presence of water ice in the lunar soil. It also studied the history of lunar impacts and the evolution of the Moon's atmosphere.

  On the 3rd of September, the rover completed all assigned tasks and entered sleep mode. Its batteries were charged while the receiver remained on in preparation for the impending lunar night. The payloads turned off and transmitted collected data to Earth via the lander. No further wake-up calls succeeded after the 28th of September when neither unit responded.

  Vikram fired its engines for a brief hop experiment on the lunar surface on the 3rd of September. The lander ascended 40 centimeters off the surface and translated a similar distance laterally across the terrain. This test demonstrated capabilities potentially useful for future sample return missions. Instruments and the rover deployment ramp retracted during the hop and redeployed afterwards.

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• 4. Reading The Moon's Hidden Secrets

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  On the 29th of August, ISRO reported that the laser-induced breakdown spectroscope instrument confirmed the presence of sulfur in the lunar surface near the south pole through first-ever in-situ measurements. While sulfur had been known from Apollo program samples before, this marked the first detection near the south pole by a rover. Noah Petro, a project scientist at NASA, described Pragyan's findings as a tremendous accomplishment.

  The rover also detected other elements including aluminum, calcium, iron, chromium, titanium, manganese, silicon, and oxygen. Scientists searched for hydrogen content within the soil samples. Chandra's Surface Thermophysical Experiment measured thermal conductivity and temperature differences at various points below the surface. Peak surface temperatures reached 355 Kelvin at the landing site, higher than the predicted 330 Kelvin.

  This unexpected warmth resulted from ChaSTE penetrating the Sun-ward facing surface with a slope of approximately six degrees. Lunar surface temperature measured from a flat surface about one meter away was found to be roughly 332 Kelvin. These variations become prominent as researchers move toward poles rather than equatorial regions.

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• 5. A Second Life In Earth Orbit

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  After completing its lunar duties, the propulsion module shifted from lunar orbit to a high Earth orbit on the 22nd of November 2023. It remains operational today conducting scientific observations of Earth. The primary objective allowed Earth observations using spectral and polarimetric instruments housed in the SHAPE payload.

  ISRO officials decided to utilize over 100 kilograms of fuel left in the propulsion module after one month of operation. This decision derived additional information for future lunar missions and determined strategies for sample return missions. The flight dynamics team developed software validated through these return maneuvers. The first lunar bound apogee raising maneuver raised the apogee from 150 kilometers to 5112 kilometers.

  The Trans-Earth Injection occurred on the 13th of October 2023 targeting an orbit of approximately 380,000 by 180,000 kilometers. Four lunar flybys followed with the last one occurring on the 7th of November 2023. The module exited lunar sphere of influence on the 10th of November 2023 and crossed perigee at about 154,000 kilometers altitude.

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• 6. Global Applause And Historic Honors

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  Chandrayaan-3's landing live stream received eight million concurrent viewers on ISRO's official YouTube channel, setting a new record for live video history. Indian Prime Minister Narendra Modi announced that the touchdown point would henceforth be known as Statio Shiv Shakti. He declared the 23rd of August as National Space Day across India.

  Josef Aschbacher, director general of the European Space Agency, called the achievement incredible and expressed thorough impressiveness. Bill Nelson, administrator of NASA, congratulated ISRO on being the fourth country to successfully soft-land a spacecraft on the Moon. Vladimir Putin sent heartfelt congratulations to Indian leaders through the Kremlin.

  The Exploration Museum bestowed upon ISRO the esteemed Leif Erikson Lunar Prize in 2023. Aviation Week Laureates Award recognized its accomplishments with the historic mission. The Chandrayaan-3 team received the prestigious 2024 John L. Jack Swigert Jr. Award for Space Exploration. The International Astronautical Federation presented Chandrayaan-3 with the World Space Award scheduled for October 14 in Milan.

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