Crucial day for Chandrayaan-3; landing module set for 'deboost' after separation today

A day after the Chandrayaan-3 spacecraft successfully underwent the final orbit manoeuvre, the lander module will undergo separation from the propulsion module on Thursday. The lander module comprises the lander (Vikram) and rover (Pragyaan) and will accomplish the rest of the journey to the Moon’s surface on its own.

The spacecraft had made a successful manoeuvre on Wednesday, putting it into an orbit of 153 km x 163 km. "With this, the lunar bound manoeuvres are completed. It's time for preparations as the Propulsion Module and the Lander Module gear up for their separate journeys," ISRO said in a post on X (formerly Twitter). 

After the separation, the lander module will undergo a "deboost" (the process of slowing down) to place it in an orbit where the Perilune (closest point to the Moon) is 30 kilometres and Apolune (farthest point from the Moon) is 100 km. From this orbit, the soft landing on the south polar region of the Moon will be attempted on August 23, ISRO has said.

According to Dr M Annadurai, Project Director of India's first Lunar Mission Chandrayaan-1, after the propulsion module says goodbye to the lander, the lander will have its initial checkups. "The four main thrusters, which will enable the lander to have a smooth landing on the lunar surface, need to be tested, as well as other sensors. Then it (lander) will take its own course to go to the near 100kmx30km orbit, and from there on August 23 early morning manoeuvres will start," he was quoted by PTI. 

The Chandrayaan-3 spacecraft entered into lunar orbit on August 5, following which orbit reduction manoeuvres were carried out on August 6, 9 and 14.

The landing module will attempt a soft landing on the South polar region of the Moon on August 23. According to ISRO chairman S Somanath, the most critical part of the landing is the process of bringing down the velocity of the lander when it begins its descent from a height of 30 km to the final landing (position). "The ability to transfer the spacecraft from horizontal to vertical direction is the "trick we have to play" here. The velocity at the starting of the landing process is almost 1.68 km per second, but this speed is horizontal to the surface of the moon. The Chandrayaan-3 here is tilted almost 90 degrees. It has to become vertical. So, this whole process of turning from horizontal to vertical is a very interesting calculation mathematically. We have done a lot of simulations. It is here where we had the problem last time (Chandrayaan-2)," Somanath said.

He added that the mission has to ensure that fuel consumption is less, the distance calculation is correct, and all the algorithms are working properly. "Extensive simulations have been done, guidance designs have been changed, and a lot of algorithms have been put in place to make sure that in all these phases the required dispersions are handled...to attempt to make a proper landing," he said.

Luna-25 enters orbit

Russia's lunar spacecraft Luna-25 entered the moon's orbit on Wednesday, days after Chandrayaan 3 did so. The Luna-25 entered the moon's orbit at 11:57 a.m. (0857 GMT). It will circle the moon, the Earth's only natural satellite for around 5 days, then change course for a soft landing on the lunar south pole is planned for Aug. 21.

"Entering lunar orbit is absolutely critical for the success of this project," Anatoly Zak, the creator and publisher of www.RussianSpaceWeb.com which tracks Russian space programmes, told Reuters. "This is a first for the post-Soviet period. Some are calling this the second lunar race so it is very important for Russia to resume this programme. Luna-25 is not just one mission - it is part of a much broader Russian strategy that stretches 10 years into the future," he added.

There could be a possible overlap of the landing dates -- August 21-23 for Luna-25 and August 23-24 for Chandrayaan-3.