December 04, 2023
In another unique experiment, like the hop experiment on the Vikram Lander, the Propulsion Module (PM) of Chandrayaan-3 was moved from an orbit around Moon to an orbit around Earth.
The primary objective of Chandrayaan-3 mission was to demonstrate soft landing near to lunar south polar region and perform experiments using the instruments on Vikram and Pragyaan.The spacecraft was launched on July 14, 2023 on-board LVM3-M4 vehicle from SDSC, SHAR. On August 23rd Vikram Lander made its historic touch down on Moon and subsequently Pragyan rover was deployed. The scientific instruments in Lander and Rover were operated continuously for 1 lunar day as per the defined mission life. The mission objectives of Chandrayaan-3 have been completely met. With regard to Propulsion Module, the main objective was to ferry the Lander module from GTO to the final lunar polar circular orbit and separate the Lander. Subsequent to separation, Spectro-polarimetry of HAbitable Planet Earth (SHAPE) payload in the PM was also operated. The initial plan was to operate this payload for about three months during the mission life of PM. The precise orbit injection by LVM3 and optimal earth / lunar burn maneuvers, resulted in the availability of over 100 kg of fuel in the PM after over one month of operations in the lunar orbit. It was decided to use the available fuel in the PM to derive additional information for future lunar missions and demonstrate the mission operation strategiesfor a sample return mission.
In order to continue SHAPE payload for Earth observation, it was decided to re-orbit the PM to a suitable Earth orbit.This mission plan was worked out considering the collision avoidance such as preventing the PM from crashing on to the Moon’s surface or entering into the Earth’s GEO belt at 36000 km and orbits below that. Considering the estimated fuel availability and the safety to GEO spacecrafts, the optimal Earth return trajectory was designed for October 2023 month.
First maneuver was performed on October 9, 2023 to raise apolune altitude to 5112 km from 150 km thus, increasing the period of orbit from 2.1 hrs to 7.2 hrs. Later, considering the estimate of available propellant, 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, propulsion module is orbiting Earth and crossedits first perigee on November 22nd with an altitude of 1.54 lakhs km. The orbit period is nearly 13 days with 27 deg inclination. The perigee and apogee altitude vary during its trajectory and the predicted minimum perigee altitude is 1.15 lakhs km. Hence as per current orbit prediction, there is no threats of close approach with any operational Earth orbiting satellites.
As per plan, SHAPE payload is being operated whenever Earth is in its field of view. Also, a special operation of the SHAPE payload was carried out on October 28, 2023 during a lunar Eclipse.The Shape payload operations will continue further.
UR Rao Satellite Centre/ISRO’s flight dynamics team has developed an analysis tool from first principles for this operation which is being validated through the return maneuvers carried out for the Chandrayaan-3 PM.
Following are the main outcome from the return maneuvers carried out on CH3 PM related to future missions:
CH-3 PM orbit after the first manoeuvre
CH-3 PM trajectory for the second manoeuvre
CH-3 PM Earth arrival trajectory
CH-3 PM orbit around Earth for next 1 year