Chandrayaan 3 Propulsion Module Moves To Earth Orbit: ISRO

The Chandrayaan 3 propulsion module (PM) has been transferred from lunar orbit to Earth's orbit, announced ISRO on Monday. This maneuver forms part of an experiment akin to the hop experiment for the Vikram lander, transitioning the Chandrayaan 3's PM from orbiting the Moon to orbiting Earth.

ISRO stated, “With regard to the PM, the primary objective was to transport the Lander module from GTO to the final lunar polar circular orbit and then detach the Lander. Following separation, the Spectro-polarimetry of Habitable Planet Earth (SHAPE) payload within the PM was activated. The initial plan was to operate this payload for approximately three months during the PM's mission lifespan.”

The space agency elaborated, “The precision of the LVM3's orbit injection and the optimal Earth/moon burn maneuvers led to a surplus of over 100 kg of fuel in the PM after more than a month in lunar orbit. This surplus fuel was repurposed to gather additional data for future lunar missions and to demonstrate mission operation strategies for a sample return mission.”

ISRO further explained that to extend the operational life of the SHAPE payload for Earth observation, they decided to reposition the PM into a suitable Earth orbit.

“This mission strategy was devised with collision avoidance considerations, such as preventing the PM from impacting the Moon’s surface or encroaching into Earth’s GEO belt at 36,000 km and lower orbits. Taking into account the available fuel and the safety of GEO spacecraft, an optimal Earth return trajectory was designed for October 2023,” ISRO stated.

ISRO added that the first maneuver, executed on October 9, elevated the apolune altitude from 150 km to 5112 km, thus extending the orbital period from 2.1 hours to 7.2 hours. After assessing the remaining propellant, the second maneuver's plan was adjusted to target an Earth orbit of 1.8 lakhs x 3.8 lakhs km.

The trans-Earth injection (TEI) maneuver took place on October 13. Post-TEI, the propulsion module made four moon flybys before exiting the Moon's Sphere of Influence (SOI) on November 10. The PM is currently orbiting Earth, having passed its first perigee on November 22nd at an altitude of 1.54 lakhs km. The orbit period was nearly 13 days with a 27-degree inclination. During its trajectory, the perigee and apogee altitudes vary, with the predicted minimum perigee altitude being 1.15 lakhs km. No close approach threats from any operational Earth-orbiting satellites have been identified.

ISRO noted, “As per the plan, the SHAPE payload is operational whenever Earth is within its field of view. Additionally, a special operation of the SHAPE payload occurred on October 28, 2023, during a Solar Eclipse. Operations of the Shape payload are set to continue.”

Furthermore, ISRO mentioned that the UR Rao Satellite Centre, home to its flight dynamics team, has developed a tool for analysing these operations from first principles, which is being validated through the return maneuvers of Chandrayaan 3.

Recalling the primary objective of the Chandrayaan 3 mission, ISRO stated it was to demonstrate a soft landing near the lunar south polar region and conduct experiments using instruments on Vikram and Pragyaan.

ISRO revealed that the main outcome from the PM's return maneuvers pertains to future missions. The planning and execution of the trajectory and maneuvers for returning from the moon to Earth were tested, along with the development and preliminary validation of software for such maneuvers. The mission also successfully tested a gravity-assisted flyby across a planet and its celestial body, and it avoided an uncontrolled crash of the PM onto the Moon's surface at the end of its life, thereby fulfilling the no debris creation requirement.