Chandrayaan-3 leaves earth’s orbit, heads towards moon: ISRO

The spacecraft will cover the distance to the moon in about four days. On August 5, it will enter lunar orbit and start going around the moon, much like it has been going around the earth until now. It will slowly get into lower and lower orbit around the moon before obtaining a circular orbit of 100 km. It is from this circular orbit that the final descent of the lander and rover module will happen around August 23.

Launched on July 14, Chandrayaan-3 is set to become India’s first spacecraft to make a soft landing on the moon. India’s previous attempt, with Chandrayaan-2 in 2019, had failed to make a successful landing.

The spacecraft will spend the next 18 days or so going around the moon and reducing the velocity and orbit in preparation for the landing. The final orbit of the integrated spacecraft would be 100*100km around the moon. The lander rover will then separate from the propulsion module and descend to the surface.

Instead of shooting directly for the moon, the current and previous Indian missions have taken the help of the earth’s gravity to increase the velocity by going around it and increasing the orbit slowly.

The landing site selected for the mission is just slightly off the one chosen for Chandrayaan-2. The spacecraft will land at 69.36oS and 32.34oE, near the moon’s southern pole. This region was selected as several craters remain permanently in shade, and can be the storehouse of water ice and precious minerals.

Chandrayaan-2, which was also designed to achieve these objectives, crash-landed just 2.1 km from the surface. To ensure the success of the current mission, several changes were made, such as sturdier legs for the lander, one less engine on it to ensure appropriate thrust, more solar panels on its surface, and the option for it to land anywhere on a larger 4km*2.4km area.

Explaining the reason for the failure of Chandrayaan-2 in its last leg, ISRO chairman S Somanath had said the five engines on the lander developed a slightly higher thrust than expected. Although still within parameters, these errors accumulated during the period the lander had to remain stable. The lander clicked pictures during the descent to determine the landing site.

When the course corrections began, the spacecraft needed to turn very fast but its ability to turn was limited by its software. The spacecraft faced contradictory requirements of slowing down the velocity at which it was coming down but accelerating forward in order to reach the correct landing site. So, when it did land, it hit the ground with a higher velocity.

If soft landing is achieved, India will become the fourth country after the US, Russia, and China to do so. It will also be the first soft landing near the moon’s southern pole. With Chandrayaan-1, India had dropped a moon impact probe closer still to the south pole at 89.7oS near Shackleton crater.