ISRO’s Unprecedented Journey to the Moon

Abstract

Chandrayaan-2, being the sequel of Indian Lunar Mission, differs with Chandrayaan-1 in targeting a specific lunar orbit. The primary ground trajectory design objective is to achieve the desired lunar orbit, from which the lander attempts soft-landing on the pre-selected landing site. The target lunar orbit is designed such that while landing, the Sun elevation rise angle is 6° on the desired site. This is to ensure the lander touchdown is close to sunrise, which in-turn will maximize the lander mission life to one lunar solar day (approximately 14 Earth days). This makes the Chandrayaan-2 trajectory design unique and challenging in itself. The maneuver strategy has been worked out to acquire the specific target lunar orbit. The objective of the powered descent phase is soft-landing over the desired site satisfying all the sensor constraints. This multi-phase lunar landing optimal control problem has been solved for trajectory design of the powered descent phase. Based on this design, the Chandrayaan-2 spacecraft has been launched on 22nd July, 2019 UT and successfully rendezvoused with the Moon on 20th August, 2019 UT and has attempted a soft-landing on 6th September, 2019 UT.