Testing Methodology of Chandrayaan-3
Authors: Veeramuthuvel P. , Kalpana K. , G Senthil Kumar , Vijaya Ganesh P. , Rajhans Chinmay Kumar , G.V.P Bharat Kumar , M.P Rijesh , Gupta Arun Kumar , G.M Mallikarjuna , Koteshwara Rao C. , Mishra Priyanka , Srikanth M. , R Jaishmi Kiruba Rajathi 
Published: September 2024

Chandrayaan-3 made a historic landing near to Lunar south pole on 23rd August, 2023. This mission has achieved all its objectives such as safe and soft landing on lunar surface, deployment of Rover and conduct of scientific experiments. All the systems of the mission performed exceptionally well as intended and predicted. Such a success was possible due to extensive and exhaustive testing carried out for the mission. The tests include special tests, flight model testing and simulations. These are system level tests conducted to evaluate the performance of integrated system. In addition to system level tests, subsystem level and component level tests were carried out as a part of spacecraft testing philosophy. Apart from ground tests, on-orbit testing of Lander systems were conducted to thoroughly evaluate flight elements before start of autonomous landing sequence.
The special tests of Chandrayaan-3 were designed to evaluate the performance of various elements involved in Lander descent trajectory by ground tests in all operating regimes. These tests include Integrated Cold Tests (ICT), Integrated Hot Tests (IHT) and Lander Leg drop tests. Custom made models and test specific facilities were realized for conducting these special tests. Special tests have provided invaluable outcomes that were incorporated in flight systems with which Chandrayaan-3 achieved its success.
Flight model tests of Chandrayaan-3 were carried out as a part of acceptance tests during spacecraft realization to ground characterize flight systems and to build a reliable spacecraft. Considering three modules of Chandrayaan-3 viz., Lander Module (LM), Propulsion Module (PM) and Rover, the flight models of this spacecraft had unique tests carried out to test and verify various interfaces. These tests improved the understanding of system level performance of spacecraft and ensured robust hardware in place for executing this mission. During the entire mission, the systems onboard had zero hardware failures or inadvertent redundancy switchover.
Exhaustive simulations carried out for comprehensively covering all the cases and driving the system to extremes for identifying various failure scenarios towards strengthening of the system independently. The Navigation, Guidance and Control Electronics in Lander performs the task of computing the navigation solution based on the absolute and inertial sensors available onboard and guiding the Lander towards the landing site using onboard thrusters and throttle-able engines. The descent operation once initiated from ground, shall be completely autonomous through an automated landing sequencer. Hence, there is a need to test the Onboard algorithm and implementation aspects very rigorously on ground to avoid any unanticipated errors. Towards this, various simulation platforms such as 6 Degree of Freedom (DOF), Onboard In Loop Simulation (OILS), Software In Loop Simulation (SILS), Hardware In Loop Simulation (HILS) and Hardware simulator were framed to thoroughly capture all aspects of the mission.
On-orbit testing of Lander systems such as sensors and propulsion system was carried out after Lander Module separation from Propulsion Module. Various sensor operations were carried out during this standalone phase of Lander Module. Two de-boost maneuvers were carried out to evaluate the performance of propulsion system as well as to achieve the intended orbit for powered descent.
This paper brings out the various tests carried out and importance of these tests for Chandrayaan-3 mission.