The efficient orbit injection and burn manoeuvres left the Propulsion Module with over 100 kg of surplus fuel after a month in lunar orbit and ISRO activated the mission to bring it back. On August 23rd, the Vikram lander made its historic touchdown on the lunar surface. Pragyan rover was deployed for scientific exploration. The PM's initial role was to transport the Lander module

In a ground breaking manoeuvre that is being looked as a follow-up to the hop experiment on the Vikram Lander, the Indian Space Research Organisation (ISRO) has successfully repositioned the Propulsion Module (PM) of Chandrayaan-3 from the lunar orbit to Earth's orbit.

This intricate operation marks a significant milestone in space exploration and showcases ISRO's commitment to advancing lunar mission capabilities as it plans to mount bigger missions in the future.

Launched on July 14, 2023, aboard the LVM3-M4 vehicle from Satish Dhawan Space Centre (SDSC), SHAR, Chandrayaan-3's primary mission was to achieve a soft landing near the Moon's south polar region and conduct experiments with the instruments onboard the Vikram lander and Pragyan rover.

On August 23rd, the Vikram lander made its historic touchdown on the lunar surface, and the Pragyan rover was deployed for scientific exploration. The mission's objectives were fully realized as the instruments operated for one lunar day, the defined mission life.

The PM's initial role was to transport the Lander module from the Geostationary Transfer Orbit (GTO) to the final lunar polar circular orbit and then release it. Following this, the Spectro-polarimetry of Habitable Planet Earth (SHAPE) payload within the PM was activated.

Although the SHAPE payload was intended to function for approximately three months, the efficient orbit injection and burn manoeuvres left the PM with over 100 kg of surplus fuel after a month in lunar orbit.

A Bold Plan

ISRO seized this opportunity to extend the mission's scope by using the remaining fuel to gather additional data for future lunar missions and to demonstrate strategies for potential sample return missions.

To facilitate ongoing Earth observations via the SHAPE payload, ISRO engineers meticulously planned the PM's re-entry into a suitable Earth orbit, ensuring collision avoidance measures to prevent impact with the Moon or interference with the Earth's geostationary belt.

The first manoeuvre to adjust the PM's trajectory occurred on October 9, raising the apolune altitude from 150 km to 5,112 km and extending the orbital period from 2.1 hours to 7.2 hours.

Propulsion Module

A subsequent manoeuvre on October 13 targeted an Earth orbit of 1.8 lakh x 3.8 lakh km. After executing the Trans-Earth Injection (TEI) manoeuvre, the PM completed four Moon fly-bys before exiting the Moon's sphere of influence on November 10.

It is now in an Earth orbit with a period of nearly 13 days and a 27-degree inclination, posing no threat to operational Earth satellites.

More Data Incoming

The SHAPE payload continues to operate whenever Earth falls within its field of view, including a special operation during the Solar Eclipse on October 28.

The UR Rao Satellite Centre/ISRO's flight dynamics team has developed and is validating an analysis tool through these manoeuvres, enhancing ISRO's capability for planning and executing complex trajectories, including gravity-assisted flybys and safe disposal strategies to avoid creating space debris.

What Did ISRO Learn From This?

The successful experiment not only boosted the Indian space agency's confidence in bringing back a spacecraft from around the Moon but also showed meticulous planning and execution by the team.

A pivotal accomplishment was the development and preliminary validation of a software module dedicated to orchestrating such manoeuvres. Additionally, strategic planning and execution were undertaken for a gravity-assisted flyby around planets or celestial bodies.

Another crucial objective was ensuring the avoidance of uncontrolled crashes on the Moon's surface during the PM's end-of-life phase, aligning with stringent requirements to prevent debris creation.

These learnings will go a long way in India's plans to send Indian astronauts to the Moon in the near future.