Chandrayaan-3 has entered its orbit circularisation phase. This means that the spacecraft has started taking a path which is “nearly” round in shape. In other words, the orbit of Chandrayaan-3 around the Moon is now almost round. After a precise manoeuvre, Chandrayaan-3 is in a near-circular orbit of 150 kilometres × 177 kilometres, the Indian Space Research Organisation (ISRO) said in a mission update. 


Chandrayaan-3 entered the orbit circularisation phase at 11:50 am IST on August 14, 2023. The spacecraft will perform the next Moon-bound manoeuvre on August 16, at around 8:30 am IST. 






In order to understand orbit circularisation in detail, ABP Live spoke to Manish Purohit, a former ISRO scientist who played a pivotal role in the Chandrayaan-2 and Mangalyaan missions, and is an expert in spacecraft solar panel technology. 


A near circular orbit is a path taken by a spacecraft or satellite around a celestial body, such as the Moon, that is almost circular, but not perfectly round, Purohit said. "In other words, it is an orbit that closely resembles a circle, but has a slight elongation or variation."


Purohit explained that orbit circularisation means giving a round shape to the path a spacecraft takes in space. Usually, a spacecraft's path appears stretched out, similar to an egg, instead of a perfect circle. "To fix this, scientists and engineers use the spacecraft's engines to push it in a certain way. This 'push' makes the path of the spacecraft become more round, or near-circular. This process is called orbit circularisation."


The former ISRO scientist said that Chandrayaan-3 reached a near-circular orbit around the Moon because of a successful orbit correction manoeuvre. "Previously, the spacecraft followed a highly elliptical path which measured around 174 km × 18,000 km when it entered lunar space."


ISRO conscientiously guided Chandrayaan-3's orbit reduction, through a sequence of controlled engines. 


"This meticulous process has culminated in Chandrayaan-3 now orbiting the Moon at approximately 151 km × 179 km, signifying a pivotal milestone in the mission's advancement," Purohit said. 


The fact that Chandrayaan-3 is currently in a near-circular orbit means that its orbital path around the Moon is almost circular, but not perfectly round. 


More about Chandrayaan-3 and its voyage towards the Moon


Chandrayaan-3 successfully underwent a planned orbit reduction manoeuvre on August 9. This brought Chandrayaan-3 closer to the Moon. In order to perform this operation, a retro-firing of engines was conducted. This was Chandrayaan-3's third lunar-bound orbit manoeuvre. 


Retro-firing allows a spacecraft to be pushed forward because its engines are burnt in a direction opposite to the way the spacecraft was fired. 


The spacecraft entered lunar orbit on August 5, and the next day, it performed its second lunar-bound orbit manoeuvre. Lunar orbit insertion of Chandrayaan-3 took place after the ISRO Telemetry, Tracking and Command Network (ISTRAC) commanded a retro-firing at the perilune. The perilune is the point in the lunar orbit at which the spacecraft is closest to the Moon. At perilune, Chandrayaan-3 performed a manoeuvre that allowed it to inject itself into the lunar orbit.


On August 4, Chandrayaan-3 covered two-thirds of the distance between Earth and Moon. On August 1, Chandrayaan-3 entered the Moon's sphere of influence, after successfully completing an orbit-raising manoeuvre or a perigee burn. A perigee burn is one which allows a spacecraft to raise its orbit.


In the early hours of August 1, Chandrayaan-3 completed its orbit around Earth following which it was injected into translunar orbit.


The Chandrayaan-3 spacecraft's voyage towards the Moon began after ISRO's largest and heaviest rocket, the Launch Vehicle Mark III (LVM3), carried India's third lunar exploration mission from Satish Dhawan Space Centre, Sriharikota, Andhra Pradesh. 


ISRO aims to land Chandrayaan-3's lander softly on the Moon's south pole. If this is achieved, India may become the fourth nation to complete the soft landing of a spacecraft on the Moon, and also the first country to land a spacecraft on the Moon's south pole.


However, Russia’s Luna 25 spacecraft, which was launched on August 11, is expected to land on the lunar south pole on August 21, which is two days before Chandrayaan’s tentative landing date. Therefore, a lunar race has ensued. The country whose spacecraft lands first on the lunar south pole will become the first country to achieve this milestone.