Chandrayaan-3 launch tomorrow: The two moon missions, compared

The third lunar mission for India will launch on Friday at 2:35 p.m. The mission’s goal is to softly land on the lunar surface and use a rover to investigate it, something that its predecessor was unable to do.

India will become the fourth nation to pull out a soft landing after China, Russia, and the United States. The post is still open following the failure of the spacecraft carrying the Japanese lander-rover and the UAE rover in 2022, as well as the missions from Israel and India in 2019 that crashed-landed.

Scientists at the Indian Space Research Organisation (Isro) have drawn lessons from the previous mission even though the mission’s goals have not changed. After a series of experiments to examine how it functions in many scenarios, including not being able to reach the landing site, having electronics or sensors fail, having a higher velocity than necessary, among others, the lander’s design was modified.

The spacecraft will progressively expand its orbit after being launched on Friday into an orbit above the Earth at a height of 179 km in a series of movements to escape the gravity of the Earth and slingshot towards the moon. The spaceship will need to be pulled into the moon’s gravity after getting close to it. After that, a next round of operations will shrink the spacecraft’s orbit to a 100×100 kilometre circle. The lander will then detach from the propulsion module and begin its powered descent while still housing the rover within.

The landing is scheduled for August 23 at lunar dawn and is anticipated to take 42 days in total. There are 14 days and nights on the moon. The lander and rover must land at the crack of dawn because they are only designed to last one lunar day because they cannot withstand the sharp drop in temperature during lunar nights.

As for the landing site, it has been moved slightly from the previous location on a plateau between two craters. The site, at around 70 degree S near the Southern pole of the moon, was selected as there are several craters here that remain permanently in shade, and can be the store-house of water ice and precious minerals. The change in the current landing site has been made on the basis of the pictures captured by the Chandrayaan-2 orbiter, which have provided a very clear map of the moon.

Despite the current mission not carrying an orbiter — it will use data from the Chandrayaan-2 orbiter — the weight of the payload is slightly more than the previous mission, with the lander making up most of the excess weight. This is most probably due to the modifications made for a safe landing.