When Vikram, the lander in ISRO’s Chandrayaan-3 mission, safely touched down on the Moon at 6:03 pm on August 23, a team of 500 scientists reflected on four years of dedicated work with immense pride.
These years were marked by an unwavering commitment to the Chandrayaan-3 project, as described by ISRO’s associate project director, K. Kalpana. Countless tests were conducted, and thousands of simulations were meticulously run. In the words of project director P. Veeramuthuvel, “Failure was not an option.” We interviewed some of the scientists from Chandrayaan-3’s core team of 34 members to uncover how they ensured the mission’s success. ISRO Chairman S. Somanath and M. Sankaran, director of UR Rao Satellite Centre – the lead center for Chandrayaan-3 – attribute the success to the tireless efforts and dedication of their scientists and engineers. According to Veeramuthuvel, Chandrayaan-3 triumphed because no detail was left to chance. “The lander was meticulously designed to adapt to any descent path it encountered. There was no room for compromise.” To achieve this, the team developed multiple mission plans and designed tests to address the shortcomings identified in Chandrayaan 2.
Putting everything to the test was crucial. The team had to anticipate every potential fault and build systems capable of overcoming them. After conducting hundreds of laboratory and field tests, they were fully confident of success on the day of landing. Over 80 integrated cold tests (without engines), integrated hot tests (with engines), and drop tests were conducted. The cold tests alone involved 25 hours of flight time and 23 sorties in an IAF helicopter. Any issues that arose were promptly addressed to ensure reliability.
One notable difference in preparation from Chandrayaan-2 was the use of a helicopter for testing Chandrayaan-3’s equipment. This allowed ISRO to test sensors at different stages of the power descent phase for five months, including tests while the lander hovered at altitudes as low as 800m and 150m, mirroring the conditions during Vikram’s lunar landing.
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While cold testing primarily focused on sensors and navigation, the hot testing at Sriharikota in Andhra Pradesh focused on engine firing. It included dry runs, static tests, closed-loop evaluations, and truncated de-boost tests under conditions similar to those on the Moon.
To ensure Vikram landed successfully on its feet, seven models of the lander were built, including three scaled-down versions. Extensive lander leg drop tests were conducted in Karnataka’s Chitradurga, where craters and boulders provided a test bed for helicopter experiments. These tests improved the team’s understanding of powered descent and landing, allowing them to assess the lander’s performance under various conditions, including steep slopes, flat surfaces, hard and soft terrain, and different combinations of horizontal and vertical velocity.
Chandrayaan-3 introduced a dedicated simulation group, a feature Chandrayaan-2 lacked. Aditya Rallapalli, project manager for simulations, revealed that they accumulated 25TB of simulation data from more than 100,000 tests. Bharath Kumar GV, deputy project director for navigation, guidance, and control (NGC) simulations, explained that they went beyond testing for nominal conditions. They predicted various parameters that could go wrong and built models to address them, implementing corrections at each level. Four different simulation test beds were used, all aimed at achieving the soft landing of Vikram on the Moon.
Finally, it was essential to ensure that the systems behaved exactly as the simulations predicted. Madhavraj, project manager for trajectory, along with Kuldeep Negi and their team, played a crucial role in this aspect. Their task was to ensure that all the planned maneuvers, including Earth-bound maneuvers, trans-lunar injection, lunar orbit insertion, lunar-bound maneuvers, and de-boosts, occurred precisely as planned. Madhavraj mentioned that they had contingency plans (Plan B) for each maneuver, but remarkably, their primary plans (Plan A) executed flawlessly every time. Rijesh MP, a deputy project director with NGC controls and dynamics, emphasized the challenge of ensuring that the guidance systems were perfectly synchronized with the engines, preventing any misinterpretation of commands in case the engines responded slowly.
In conclusion, the success of Chandrayaan-3 was the result of years of meticulous planning, rigorous testing, and the dedication of a highly skilled team of scientists and engineers who left no stone unturned to ensure a successful lunar landing.
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