India has achieved a remarkable feat in space exploration by successfully bringing the Chandrayaan-3 Propulsion Module (PM) back to Earth orbit from Moon orbit, demonstrating the technology and capability to return from the lunar surface. This achievement marks the first instance where a nation has successfully recovered a spacecraft from the Moon and transported it back to orbit around Earth.
The Chandrayaan-3 mission was launched on July 14, 2023, from the Satish Dhawan Space Centre on board a Launch Vehicle Mark-3 (LVM3) rocket. The mission consisted of a lunar lander, Vikram, and a lunar rover, Pragyan, similar to those launched aboard Chandrayaan-2 in 2019. The mission objectives were to demonstrate a safe and soft landing on the lunar surface, showcase the rover’s mobility on the Moon, and conduct in situ scientific experiments.
The Propulsion Module was instrumental in transporting Vikram and Pragyan from launch to a Moon orbit. On August 5, it entered lunar orbit, following which the lander was deployed on August 20. Finally, at 18:03 IST (12:33 UTC) on August 23, the lander docked successfully at a site near the Moon’s south polar region. This achievement establishes India as the fourth country to accomplish a successful Moon landing and the first nation to do so near the Moon’s south pole.
The lander deployed the rover on the same day, and both began operations on the lunar surface. The lander and the rover carried various scientific instruments to study the lunar topography, elemental abundance, mineralogy, lunar exosphere, and hydroxyl and water ice signatures. The lander also had a Laser Retroreflector Array (LRA) provided by NASA, which future lunar missions can use for precise landing and navigation.
The lunar lander and the rover were designed to operate for one lunar day (about 14 Earth days) but exceeded their expected lifespan and performed additional tasks. On September 3, the lander hopped and repositioned itself 30-40 cm (12-16 inches) away from its landing site, using its throttle-able engines. This accomplishment showed that the Indian Space Research Organisation (ISRO) could restart engines on the Moon and operate equipment, which was not foreseen, the national space agency stated in a release.
The lander and the rover completed their mission objectives by September 22 and entered sleep mode, hoping to revive for extra tasks on the next lunar day. However, they missed the wake-up call on October 7 and were declared lost on October 10. The Chandrayaan-2 Orbiter, orbiting the Moon since 2019, relayed the data the lander and the rover collected to Earth.
Meanwhile, the PM, which had remained in the lunar orbit after releasing the lander, had a significant amount of fuel left. ISRO 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.
Four Flybys
The PM conducted four flybys near the Moon from October 13 to November 10 by adjusting the spacecraft’s orbit with the help of thrusters. These flybys allowed the spacecraft to approach the lunar surface as close as 100 km (62 miles) and capture detailed images of the landing site and other areas of significance. Additionally, the spacecraft carried a scientific instrument called SHAPE (Spectro-polarimetry of HAbitable Planet Earth), which measured the polarization of sunlight reflected by the Moon.
SHAPE, an instrument on Chandrayaan-3, aids scientists in studying the suitability of Earth and other exoplanets for life by analyzing their atmospheric and surface features. Through examining sunlight polarization, SHAPE offers valuable information about the atmosphere’s composition, the presence of clouds, and other factors crucial for habitability. This data is significant in evaluating the potential habitability of other planets and enhancing our understanding of Earth’s environment. SHAPE’s observations align with Chandrayaan-3’s objectives and expand our knowledge of habitable conditions on our planet and beyond.
Initially, the intention was to utilize this payload for roughly three months during the PM mission. However, thanks to the accurate placement of the spacecraft into its orbit by LVM3 and effective manoeuvres performed near Earth and the Moon, the PM had a surplus of over 100 kg of fuel remaining even after operating in lunar orbit for more than a month.
The team decided to use the remaining fuel in the PM to collect additional data for future lunar missions and demonstrate operational strategies for a sample return mission. They also determined that repositioning the PM to a suitable orbit around Earth would allow the SHAPE payload to continue its observations.
Return Mode
To prioritize safety and prevent any mishaps, the mission plan included precautions to avoid the PM crashing onto the lunar surface or entering the Earth’s GEO belt at a distance of 36,000 km. ISRO acknowledged the importance of the available fuel and the safety of the GEO spacecraft and accordingly devised an optimal trajectory for the PM’s return to Earth in October 2023.
The PM adjusted its orbit, transitioning away from the Moon’s gravitational influence. It is now situated in an Earth orbit with specific characteristics to ensure safety and minimize any risks of colliding with other satellites.
Optimizing the Return
Journey Back to Earth
Following the successful lunar operations, the Chandrayaan-3 team crafted an optimal Earth return trajectory, marking a critical phase in the mission’s extended objectives. This strategic manoeuvre aimed to bring the PM back from the lunar orbit to Earth, showcasing the precision and planning prowess of ISRO.
Initial Orbit Adjustment (October 9):
§ The first manoeuvre on October 9 aimed to elevate the highest point of the orbit (apolune altitude)
§ Apolune Altitude: Increased from a mere 150 km to an impressive 5,112 km
§ Orbit Period: Significantly extended from 2.1 hours to a more complex 7.2 hours
Revised Plan for Earth Orbit (October 9):
§ Adjusting to available propellant, the team revised the plan to position the PM in an Earth orbit with dimensions of 1.8 lakh km x 3.8 lakh km (180,000 km x 380,000 km). This ambitious objective highlighted ISRO’s commitment to pushing boundaries in space exploration.
Trans-Earth Injection (October 13):
§ A pivotal moment in the mission occurred on October 13 with the successful execution of the Trans-Earth Injection manoeuvre. This precise manoeuvre set the PM on a trajectory towards Earth
§ The module’s trajectory included a fascinating journey, flying by the Moon four times before finally departing the Moon’s sphere of influence on November 10
Current Earth Orbit Status (as of November 22):
§ On November 22, the PM reached its closest point in the current Earth orbit, maintaining a safe distance of 154,000 km
§ The orbit period has evolved, taking approximately 13 days for one complete orbit
§ The PM orbits Earth in a complex pattern with varying closest and farthest locations, with an orbital inclination of 27 degrees. Its anticipated lowest nearest point is 115,000 km
Timely Arrival at Earth’s Orbit:
§ The strategic manoeuvres initiated on October 9 have proved effective, with the PM successfully reaching Earth’s orbit on November 4. This 44-day journey underscores the precision and efficiency of ISRO’s planning and execution
The primary outcomes of the return manoeuvres performed on CH3 PM for future missions were as follows:
- Determining and executing the trajectory and manoeuvres required to return from the Moon to Earth.
- Developing a software module to facilitate planning such a manoeuvre and conducting preliminary testing of its functionality.
- Strategizing and successfully executing a flyby around other planets or celestial bodies to take advantage of their gravitational pull and assist in the spacecraft’s trajectory.
- Ensuring that the PM does not crash uncontrolled onto the Moon’s surface upon reaching the end of its lifespan, effectively meeting the requirement of preventing debris creation.
These crucial moments in the Chandrayaan-3 mission showcase the technical accomplishments of orbit adjustments and intricate manoeuvres and establish a strong foundation for upcoming missions.
