On July 14, 2023, ISRO launched its ambitious third lunar mission Chandrayaan 3. On August 23, 2023, ISRO made history by successfully landing India’s Chandrayaan-3 mission on the Moon’s south pole.
The primary mission objective was to achieve a soft landing near the lunar south polar region and perform experiments using the instruments on Vikram and Pragyaan. The mission objectives of Chandrayaan-3 have been completely met.
Regarding the Propulsion Module, the primary goal was to transport the Lander module from GTO to the final lunar polar circular orbit and then separate the Lander. The PM’s Spectro-polarimetry of the HAbitable Planet Earth (SHAPE) payload was activated after the separation.
Originally intended to operate for approximately three months during the PM’s mission life, precise orbit injections by LVM3 and optimal earth/lunar burn maneuvers resulted in over 100 kg of available fuel in the PM after more than a month of lunar orbit operations. Consequently, it was decided to utilize this surplus fuel to gather additional data for future lunar missions and demonstrate operational strategies for a sample return mission.
To keep observing Earth with the SHAPE payload, they decided to move the Propulsion Module (PM) to a suitable orbit around Earth. They planned this carefully to avoid a collision, like ensuring the PM doesn’t crash the Moon’s surface or go into Earth’s GEO belt at 36000 km and orbit below that. Taking into account their fuel and the GEO spacecraft’s safety, they devised the best plan for the PM to return to Earth in October 2023.
ISRO mentioned, “First maneuver was performed on October 9, 2023, to raise apolune altitude to 5112 km from 150 km, thus increasing the orbit period from 2.1 to 7.2 hrs. Later, considering the estimate of available fuel, the second maneuver plan was revised to target an Earth orbit of 1.8 lakhs x 3.8 lakhs km. The Trans-Earthinjection (TEI)maneuver was performed on October 13, 2023.”
“In thepost-TEI maneuver realized orbit, propulsion module made four Moon fly-bys before departing Moon SOI on November 10. Currently, the propulsion module is orbiting Earth and crossed its first perigee on November 22 with an altitude of 1.54 lakhs km. The orbit period is nearly 13 days with 27 deg inclination.”
“The perigee and apogee altitudes vary during their trajectory, and the predicted minimum perigee altitude is 1.15 lakhs km. Hence, per current orbit prediction, there are no threats of close approach with any operational Earth-orbiting satellites.”
According to the plan, they will use the SHAPE payload whenever Earth is in its field of view. They even did a special operation during a Solar Eclipse on October 28, 2023. They’re going to keep using SHAPE.
UR Rao Satellite Centre/ISRO’s flight dynamics team developed an analysis tool for this operation from the first principles. They’re ensuring it works well by testing it during the Chandrayaan-3 PM return maneuvers.