Bengaluru: 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 the Moon to an orbit around Earth.
The primary objective of the Chandrayaan-3 mission was to demonstrate a 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 an LVM3-M4 vehicle from SDSC, SHAR. On August 23rd Vikram Lander made its historic touchdown 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. About the Propulsion Module, the main objective was to ferry the Lander module from GTO to the final lunar polar circular orbit and separate the Lander.
After separation, the Spectro-polarimetry of the 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 strategies for a sample return mission.
To continue the 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 collision avoidance such as preventing the PM from crashing onto 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 of the GEO spacecraft, the optimal Earth return trajectory was designed for October 2023 month.
The first maneuver was performed on October 9, 2023, to raise the 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 the post-TEI maneuver realized orbit, the 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 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 threat of close approach with any operational Earth-orbiting satellites.
As per the plan, the 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 Solar 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 validated through the return maneuvers for the Chandrayaan-3 PM.
The following are the main outcomes from the return maneuvers carried out on CH3 PM related to future missions:
- Planning and execution of trajectory and maneuvers to return from the Moon to Earth.
- Development of a software module to plan such a maneuver and its preliminary validation.
- Planning and executing a gravity-assisted flyby across a planet/ celestial body.
- Avoiding uncontrolled crashing of the PM on the Moon’s surface at the end of life of PM thus meeting the requirements of no debris creation.
