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Chandrayaan-3, India’s third Moon mission, took off from the Sriharikota launching range on Friday. The mission hopes to put behind the failure of Chandrayaan-2, which had crashed on the lunar surface in 2019. Important improvements have been made in the design to ensure that another accident is avoided.
While attempting a soft-landing on September 7, 2019, Chandrayaan-2 had failed to reduce its speed to the desired level in the final seconds of descent. Scientists later detected problems in both the software and the hardware — in consequence, the software and hardware in Chandrayaan-3 have been equipped with several additional capabilities.
A Lander does not have wheels; it has stilts, or legs, which are supposed to touch down on the lunar surface, and then stabilise. Chandrayaan-2 lost control over its descent around 7.2 km from the surface of the Moon. Its communications system relayed data of the loss of control up to around 400 m above the surface. The Lander had slowed down to about 580 km/hr when it crashed.
The legs of Chandrayaan-3 have been strengthened to ensure that it would be able to land, and stabilise, even at a speed of 3 m/sec, or 10.8 km/hour. Of course, this would be of little use if Chandrayaan-3 is struck by a problem similar to the one that crashed Chandrayaan-2, but this can certainly avert many other kinds of troubles in case of a rough landing.
The Chandrayaan-3 Lander is carrying more fuel than Chandrayaan-2. This has been done to ensure that the Lander is able to make a last-minute change in its landing site, if it needs to.
The Chandrayaan-2 Lander too had the ability to change its course if the onboard cameras detected a boulder, a crater, or any other lunar surface feature that would make the landing unstable. The extra fuel is meant to enhance this capability.
The Chandrayaan-3 Lander has solar panels on four sides, instead of only two in Chandrayaan-2. This is to ensure that the Lander continues to draw solar power, even if it lands in a wrong direction, or tumbles over. At least one or two of its sides would always be facing the Sun, and remain active.
Additional navigational and guidance instruments are on board Chandrayaan-3 to continuously monitor the Lander’s speed, and make the necessary corrections. This includes an instrument called Laser Doppler Velocimeter, which will fire laser beams to the lunar surface to calculate the Lander’s speed. New sensors and cameras have also been added.
The hazard detection and avoidance camera and the processing algorithm have been upgraded. The navigation and guidance software has also been updated. Multiple layers of redundancies have been added to ensure that if one system does not work because of any reason, something else will.
The Lander has been subjected to multiple stress tests and experiments,
including dropping it from helicopters. ISRO created several kinds of test beds at one of its facilities to simulate lunar landing conditions.
“We have done whatever we could think of in terms of probabilities in the last two years and it is with this confidence that we are moving to launch Chandrayaan-3,” ISRO chairman S Somanath had said a couple of days ago.
