Chandrayaan-3: Welcome back to "Science For Everyone", ABP Live's weekly science column. Last week, we discussed why the invention of the atomic bomb is a quintessence of scientific triumph that introduced the world to the marvels of particle physics, and how it shaped scientific discoveries over the years. This week, we explain why Chandrayaan-2, India's second lunar exploration mission, failed, and what changes the Indian Space Research Organisation (ISRO) has made to ensure the success of Chandrayaan-3, the country's third lunar exploration mission. Chandrayaan-3 is slated to land on the Moon on August 23, at around 5:57 pm IST. If Chandrayaan-3 lands on the Moon's south pole before Russia's Luna 25, India will become the first country to softly land a spacecraft on the lunar south pole.
Chandrayaan-2 and Chandrayaan-3 are almost identical, except that Chandrayaan-2 included an orbiter, but Chandrayaan-3 is not carrying an orbiter. The Chandrayaan-2 spacecraft consisted of an orbiter, a lander and a rover called Pragyan. While the lander, called Vikram, failed to make the desired smooth landing, the other aspects of the mission were successful.
ISRO intended to land Vikram on a smooth plain on the lunar surface about 600 kilometres from the south pole, but lost contact with the lander shortly before the touchdown, which was scheduled to occur on September 7, 2019. This aspect of the Chandrayaan-2 mission failed due to a software glitch. Communication between the lander and mission control station on Earth was lost after Vikram reached an altitude of 2.1 kilometres above the Moon's surface.
Pragyan was destroyed along with Vikram when the lander crash-landed on the Moon.
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Changes Made In Vikram To Ensure Chandrayaan's Success
In order to ensure that Chandrayaan-3 is a success, ISRO has made some changes in the design and capabilities of Vikram. These strategic enhancements are expected to increase the chances of Chandrayaan-3's Vikram landing on the Moon's south pole.
The changes ISRO has made to ensure Vikram lands safely on the Moon include reinforced landing legs, enhanced sensors, an expanded solar array, sophisticated software, enhanced engine throttling, and optimised engine configuration.
"While Chandrayaan-2's Vikram had five 800 Newton engines, Chandrayaan-3's Vikram will have four throttleable engines. ISRO has added a Laser Doppler Velocimeter for precise guidance during the autonomous landing manoeuvre, the landing legs have been made stronger, and redundancy has been added to ensure an autonomous landing even if all sensors and engines fail to operate," Debadatta Mishra, a former ISRO scientist, and co-founder of Erisha Space, a New Delhi-based space-tech firm, told ABP Live.
A throttleable engine is one whose thrust can be varied. The fact that redundancy has been added means that extra components, that are not necessarily functional, have been included to ensure that Vikram autonomously lands even if all sensors and engines fail. The Laser Doppler Velocimeter is a sensor the lander has been equipped with. A laser doppler velocimeter measures local, instantaneous fluid velocities by detecting the frequency of light scattered by small particles suspended in the fluid. In the case of Vikram, the Laser Doppler Velocimeter will measure the velocity of the lunar air.
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“The Vikram lander's landing legs have been fortified to robustly withstand the impact of landing, ensuring the module can confidently handle the forceful thud upon contact with the lunar surface,” Manish Purohit, a former ISRO scientist who was involved in the Chandrayaan-2 and Mangalyaan mission, and is an expert in spacecraft solar panel technology, told ABP Live.
The sensors on Chandrayaan-3’s Vikram are more advanced and responsive than Chandrayaan-2’s lander, and this will allow it to make faster and more informed decisions during the landing phase, Purohit explained. “These heightened sensing capabilities empower the lander with real-time data for precise course adjustments.”
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The solar array has a higher power generation capacity than that of Chandrayaan-2’s Vikram because the array’s size has been increased to ensure that the lander has a consistent and reliable power source during its lunar descent, and also while performing other operations on the Moon.
The lander’s software has been upgraded, and it now has better error-handling capabilities, Purohit said. “The improved software is engineered to effectively navigate potential challenges and anomalies that may arise during the mission.”
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Since Vikram’s engines have refined throttling capabilities, it will be possible for ISRO to execute precisely controlled manoeuvres and adjustments during the lander’s descent.
The fact that Chandrayaan-3’s Vikram has four engines while Chandrayaan-2’s lander had five engines does not only mean a simplified design, but also allows space to be increased for fuel storage, Purohit explained. “This surplus fuel reservoir equips the lander to adeptly manage unforeseen or off-nominal scenarios.”
ISRO has made improvements in the instruments Vikram is equipped with to ensure that the lander can efficiently detect hazards at the time of landing, Purohit said. “Coupled with upgraded velocimeters, the lander can make real-time decisions during the delicate phase of soft landing, enhancing precision and safety.”
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