ISRO has announced a unique experiment involving the Propulsion Module (PM) of Chandrayaan-3. Initially designed to facilitate the soft landing of the Vikram lander and Pragyan rover near the lunar south polar region, the mission achieved its primary objectives with the historic touchdown of the Vikram lander on the Moon on August 23.
The scientific instruments on the lander and rover operated continuously for one lunar day, meeting the mission goals.
Subsequently, the PM, responsible for transporting the lander from Geostationary Transfer Orbit (GTO) to the final lunar polar circular orbit, successfully separated the lander and operated the SHAPE payload.
With over 100 kg of fuel remaining in the PM after a month of lunar orbit operations, ISRO decided to utilize it for additional information gathering and future mission demonstrations. The plan involved re-orbiting the PM to a suitable Earth orbit for continued SHAPE payload observations.
The first maneuver on October 9, 2023, raised the apolune altitude to 5,112 km, and subsequent adjustments targeted an Earth orbit of 1.8 lakh x 3.8 lakh km.
The Trans-Earth Injection (TEI) maneuver on October 13 marked the beginning of the return journey, with the PM making four Moon fly-bys before leaving the Moon's sphere of influence on November 10.
As of November 22, the PM is orbiting Earth with a nearly 13-day period and a 27-degree inclination.
ISRO assures that, based on current predictions, there is no threat of close approach to operational Earth-orbiting satellites.
The SHAPE payload operations continue during Earth's field of view, and special operations were conducted during a solar eclipse on October 28, 2023.
The return maneuvers of the PM have yielded valuable outcomes for future missions.
This includes the planning and execution of trajectory and maneuvers for returning from the Moon to Earth, the development of a software module for maneuver planning and its preliminary validation, planning and execution of gravity-assisted fly-bys, and ensuring the controlled end-of-life descent to avoid debris creation on the Moon's surface.
The UR Rao Satellite Centre/ISRO's flight dynamics team played a crucial role in developing analysis tools for these operations.
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