Perilune, Soft Landing, Orbit Circularisation – Scientific Jargons Used For Chandrayaan-3

Chandrayaan-3 is set to make history on August 23, 2023, by becoming the first spacecraft to softly land on the lunar south pole. Since Chandrayaan-3 was launched on July 14, 2023, the Indian Space Research Organisation (ISRO) has been posting mission updates. These announcements include several scientific jargons. Some examples are lander, rover, lander module, propulsion module, Earth-bound manoeuvre, lunar-bound manoeuvre, retro burning, perigee burn, orbit circularisation, perilune, and soft landing, among others.

Here is a breakdown of the complex terms.


A lander is a spacecraft designed to land on the surface of a celestial body, such as a planet or its moon. A lander is immobile, remains fixed in a particular position, and performs all operations from that location. Chandrayaan-3’s lander is called Vikram.


A rover is a spacecraft designed to explore the surface of a planet or Moon. A rover is not stationary, and moves on the surface of the celestial body to perform experiments. Chandrayaan-3’s rover is called Pragyan.

Lander module

Chandrayaan-3’s rover is fitted inside the lander, and together, they are called the lander module. In other words, the lander module refers to the complete configuration of the lander and the rover fitted inside the former. After Vikram lands on the Moon, a rover ramp will be unfurled, and Pragyan will embark on its journey on the Moon.

Propulsion module

Chandrayaan-3’s propulsion module was designed to carry the lander module to a 100-kilometre lunar orbit. After this, the propulsion module and the lander module separated. The lander module continued on its journey towards the lunar surface, but the propulsion module remained in orbit. The propulsion module is acting as a communications relay satellite for the lander module.

Earth-bound manoeuvre

Earth-bound manoeuvre, also known as Earth-bound perigee firing, refers to an orbit-raising manoeuvre performed by a spacecraft at Earth’s perigee, or the farthest point in the orbit of the planet.

Trans-lunar orbit

A translunar orbit refers to an elliptical orbit that must be taken by a spacecraft to reach lunar orbit from Earth orbit.


In retro-burning, a spacecraft is burnt in a direction opposite to the way it was fired in order to push it forward.

Perigee burn

A perigee burn, also known as an orbit-raising manoeuvre, is one which allows a spacecraft to raise its orbit.


The point in the lunar orbit at which a spacecraft is closest to the Moon is known as perilune. At perilune, Chandrayaan-3 performed a manoeuvre that allowed it to inject itself into the lunar orbit.

Orbit circularisation

The orbit circularisation phase refers to the stage in which a spacecraft starts taking a path which is “nearly” round in shape. In other words, the orbit of the spacecraft becomes almost round. Chandrayaan-3 entered the orbit circularisation phase at 11:50 am IST on August 14, 2023.

“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,” Manish Purohit, a former ISRO scientist, told ABP Live.

Soft landing

Chandrayaan-3 is attempting a soft landing on the lunar south pole. Soft landing means that a spacecraft safely touches down on a celestial body without its components being harmed. This is important to ensure that all parts remain functional. In other words, soft landing is the landing performed without a jerk or shock.

In basic terms, a ‘soft landing’ means safely touching down a spacecraft without causing significant harm to the spacecraft or its contents. This is crucial because it safeguards the functionality of the equipment onboard, allowing for successful data collection and scientific exploration. In contrast, a hard landing could result in detrimental effects on the spacecraft and its mission due to potential damage,” Purohit explained.

Soft landing is preferred over hard landing because it allows scientific experiments to be performed accurately.

If Chandrayaan-3 softly lands on the lunar south pole, India will become the first country to achieve this.

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