Chandrayaan-3, the succeeding mission to Chandrayaan-2, is nearing its launch date. The two missions are almost identical, except that Chandrayaan-2 included an orbiter, but Chandrayaan-3 will not carry any orbiter. Chandrayaan-3 is scheduled for launch on July 14, 2023, at 2:45 pm IST, about four years after Chandrayaan-2 was launched on July 22, 2019. 


Chandrayaan-3 will be a repeat of Chandrayaan-2, but will not have an orbiter. Similar to Chandrayaan-2, Chandrayaan-3 will be launched into space using the Geosynchronous Satellite Launch Vehicle Mark III. 


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What went wrong with Chandrayaan-2


The Chandrayaan-2 spacecraft consisted of an orbiter, a lander and a rover. While the lander, called Vikram, failed to make the desired smooth landing, the other aspects of the mission were successful. 


The Indian Space Research Organisation (ISRO) aimed to land Chandrayaan-2's Vikram lander 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. 


According to ISRO, normal performance of the Vikram lander was observed up to an altitude of 2.1 kilometres. However, communication between the lander and the mission control station on Earth was lost after that. 


Vikram followed the planned descent trajectory from its orbit of 35 kilometres to just below two kilometres above the lunar surface. 


The rover, called Pragyan, was destroyed along with Vikram when the lander crash-landed on the Moon.


However, the Chandrayaan-2 orbiter was placed in the intended orbit.


On September 10, 2019, ISRO posted an update that the Chandrayaan-2 orbiter had located Vikram lander. 


NASA's Lunar Reconnaissance Orbiter (LRO) captured the first mosaic of Vikram's landing site on September 17, 2019. The mosaic, released on September 26, was used to search for signs of Vikram. 


Shanmuga Subramanian, an engineer from Chennai, successfully identified the debris formed from the crash of Vikram, and contacted the LRO project to reveal his discovery, according to NASA. Subramanian identified debris about 750 metres northwest of the main crash site. 


The team compared before and after images, but was not able to decipher information properly because of the poor illumination of the impact point when the images of the first mosaic were obtained. 


However, a subsequent image sequence captured on November 11 had the best pixel scale and lighting conditions, and showed best the impact crater and extensive debris field, according to NASA. 


About 90 to 95 per cent of Chandrayaan-2's mission objectives have been accomplished.


How Chandrayaan-3 is different from Chandrayaan-2


Apart from the fact that Chandrayaan-3 will not carry an orbiter, the spacecraft is different from Chandrayaan-2 because it will carry a payload its preceding mission did not have: Spectro-polarimetry of HAbitable Planet Earth (SHAPE). Chandrayaan-3's propulsion module is equipped with SHAPE.


The function of SHAPE is to study the spectral and polarimetric measurements of Earth from lunar orbit. This means that SHAPE will analyse the spectro-polarimetric signatures of Earth. 


According to the University of Maryland, Baltimore County (UMBC) Observatory, spectro-polarimetry is a technique which involves the polarisation of light by splitting the incoming light into its constituent colours, and then analysing the polarisation of each colour individually. 


Understanding the spectro-polarimetric signatures of Earth can help scientists analyse the reflected light from exoplanets and determine whether they would qualify for habitability.