A view of the moon as viewed by the Chandrayaan-3 lander during Lunar Orbit Insertion on August 5, 2023 in this screengrab from a video released August 6, 2023.
Credit: Reuters/ISRO
Extensive studies and simulations have supplemented the design of Chandrayaan-3 to ensure its safe landing on the lunar surface, Indian Space Research Organisation (Isro) Chairman S Somanath said on Tuesday.
The most critical part of the landing — scheduled for August 23 — will be reducing the lander’s velocity, Somanath said during an online lecture on the lunar mission, hosted by NGO Disha Bharat.
The lander’s velocity at the beginning of the descent (from a height of 30 km) will be almost 1.68 km per second. Its velocity at touch-down has been identified as up to three metres per second.
The process of shifting the lander’s trajectory – from horizontal to vertical – involves “interesting mathematical calculations” and extensive simulations. “Here, we had a problem last time (the failed landing of Chandrayaan-2). We need to ensure that the right amount of fuel is consumed, the distance calculated is correct, and all the algorithms are working properly,” Somanath said.
Isro has conducted lander leg drop tests to demonstrate the stability of the lander in various touchdown conditions.
During the descent, at a height of 7.4 km, there will be a phase where some of the instruments are calibrated; the sensors will be verified at 800 metres or 1,300 metres. At 150 metres, a hazard verification will be done, to decide whether the lander could land vertically there itself or move laterally, to a maximum extent of 150 metres, to avoid boulders or craters.
The Isro Chairman said “hundreds of simulations” were done to lock the landing within the identified site which measures 4 km x 2.4 km (increased from the 0.5 km x 0.5 km site identified for Chandrayaan-2). "All locations are not safe, there are boulders and craters on the site; we will have to make local decisions on where to land,” he said.
Isro has commenced the mission’s moon-bound manoeuvres, with a retro-firing of engines on Sunday bringing the spacecraft to a 170 km x 4,313 km orbit. On Wednesday, the orbit will be further reduced and another firing, on August 14, will achieve a 100 km x 100 km orbit. On August 17, the landing module will be separated from the propulsion module, to set up the powered descent.