Eye On Moon Rocks, ISRO Chief On "Unconventional" Chandrayaan-3 Experiment

ISRO continues to surprise India with Chandrayaan-3. Now the orbiting satellite of the Chandrayaan-3 mission called the propulsion module - which was orbiting the Moon - has been extracted from the Moon orbit and placed in an orbit around Earth. This is a very critical but important learning for India to prepare for a sample-return mission from the Moon.

ISRO chairman S Somanath told NDTV, "It is all about preparing for ISRO's next big planetary outing to bring back moon rocks to India in a sample-return mission."

On today's achievement, the space agency said, "Returns to home Earth: Chandrayaan-3 Propulsion Module moved from lunar orbit to Earth's orbit". In reality, it is close to home only as an orbiting satellite.

In the cost of a single mission, ISRO with Chandrayaan-3 has experimented thrice over and given India the benefit of what could have been achieved through subsequent missions. Chandrayaan-3 costs less than Rs 700 crore and ISRO says, "The mission objectives have been completely met."

"The 'naya ISRO' which is sharply focusing on R&D is really all about doing unconventional things, taking calculated risks to get more bang for the same buck. India's space research was already all about frugal technology development and now it is getting so much more from less! Teams are being encouraged to do novel things and think like a nimble start-up would," added Mr Somanath.

"Chandrayaan-3's homeward bound mission plan was the best use of a gravity assist experiment and the young team learnt a lot of new complex mathematics in a real life planetary experiment which is hard to simulate on a computer".

The soft landing on the Moon, the Vikram hop experiment and the return to Earth orbit of the Chandrayaan-3 propulsion module are all essential learnings in the unforgiving lunar environment - baby steps to ultimately meet the objective of sending an Indian to the Moon by 2040 as announced recently by Prime Minister Narendra Modi.

"The newly energised ISRO will work hard to make sending an Indian to the moon by 2040 a reality as desired by Prime Minister Narendra Modi, Chandrayaan-3's success only boosts the morale further that India can do it," the ISRO chief said.

In a series of intricate operations, ISRO successfully brought the Moon-orbiting Chandrayaan-3 satellite into the Earth orbit. A tricky manoeuvre carefully executed by the scientists from ISRO has now led the propulsion module of the Chandrayaan-3 to orbit the Earth.

This unique experiment was not part of the original mission plan but like the hop experiment of Vikram, an important step mastered to get Moon rocks in the next Indian mission.

Just as the Vikram lander and the Pragyaan rover were completing their mandated tasks nearer to the south pole of the moon and before they were put to sleep for the long 14-day lunar night, on September 3, the scientists at the space agency conducted a hop experiment. The engines of the lander were reignited and the lander was lifted 40 centimetres above the lunar surface and safely landed back. This was a very crucial learning step and was undertaken by ISRO since there was extra fuel left over in the lander.

These simple experiments give Team Chandrayaan the much-needed confidence that whenever a sample return is planned next, the ISRO will be ready. How much soever one simulates these on computers there is no substitute for an actual test in the harsh lunar environment. The hop experiment was also not part of the original plan. Still, the young team executed it with perfection since, anyway, Vikram Lander was heading to become 'India's permanent ambassador at Shiv Shakti Point', explained S Somanath.

ISRO said, "Chandrayaan-3's Propulsion Module (PM) took a successful detour! In another unique experiment, the PM is brought from lunar orbit to Earth's orbit. An orbit-raising manoeuvre and a Trans-Earth injection manoeuvre placed PM in an Earth-bound orbit."

The Propulsion Module was orbiting the moon in a circular 100-kilometre orbit and the only scientific instrument it had more or less completed its tasks. Since the orbiting lunar propulsion module still had enough fuel left in it, the scientists at ISRO figured out why not extract the PM from around the moon and bring it back into an Earth-bound orbit. This is a very tricky operation and is the opposite of a lunar injection.

In a statement, ISRO said this latest experiment "was worked out considering the collision avoidance such as preventing the PM from crashing onto the Moon's surface or entering into the Earth's GEO belt at 36,000 km and orbits below that. Considering the estimated fuel availability and the safety of GEO space crafts, the optimal Earth return trajectory was designed for October 2023 month. The first manoeuvre was performed on October 9 to raise apolune altitude to 5112 km from 150 km thus, increasing the period of orbit from 2.1 hours to 7.2 hours. Later, considering the estimate of available propellant, the second manoeuvre plan was revised to target an Earth orbit of 1.8 lakhs x 3.8 lakhs km. The Trans-Earth injection (TEI) manoeuvre was performed on October 13, 2023. In the post-TEI manoeuvre realised orbit, the propulsion module made four Moon fly-bys before departing Moon SOI on November 10. Currently, the propulsion module is orbiting Earth and cross-edits the 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 lakh km. Hence as per current orbit prediction, there is no threat of close approach with any operational Earth orbiting satellites."

India successfully soft landed on the moon on August 23 and Vikram lander and the Pragyaan rover completed their 14-day tasks and went into a lunar slumber.

India is already planning the next lunar mission in partnership with Japan.

Dr M Sankaran, Director of the UR Rao Satellite Center in Bengaluru, had said the next obvious logical step for India is to undertake a sample return mission from the moon.