'Chandrayaan-3's landing may get postponed to Aug 27 if...,' says Isro scientist ahead of planned touchdown on Moon

A senior ISRO scientist on Monday said that the Chandrayaan-3's landing on Moon may get postponed to August 27 if the space agency finds, two hours before the planned touchdown, the position of the lander is not suitable for the descent. The scientist also said that if the space agency decides to attempt touchdown on August 27 then the landing will be 400-450 km away from the main site planned for August 23. 

Nilesh M Desai, Director at Center for Space Applications-ISRO, Ahmedabad, said that two hours before Chandrayaan-3's scheduled landing on the lunar surface, the space agency will check the position of the lander and the Moon and after that, it will take a decision on landing.

"If we feel that the position of the lander is not suitable for landing, then we will extend it to August 27. We will try to land the lander on August 23," he said.

The ISRO on Sunday said Chandrayaan-3 is set to land on the lunar surface around 6:04 pm on August 23. 

Desai said that the Chandrayaan-3's lander will most probably land on August 23 but if any complication occurs, then the landing will be attempted on August 27 and all the preparations have been made. The spacecraft, which is currently in a 25 km x 134 km orbit, will attempt to land from 30 km height at a velocity of 1.68 km per second, which is very high.    

  

The scientist said that upon descent, the Moon's gravity will pull the lander module down. "We will have to retro-fire the thruster engine to slow down the speed to zero by the time it reaches the lunar surface. We have placed four thruster engines in the lander module. From 30 km, it (the lander) will come down to 7.5 km, then it will come down to 6.8 km. We will then stop two engines."  

Desai said that at 30 km height, the speed of the spacecraft will be 1.68 km per second but its speed will be reduced to 350 metres per second by the time it reaches 6.8 km. He said engines will give reverse thrust to bring down the speed. From 6.8 km, the lander will come down to 800 meters, and its speed will be almost zero meter per second.   

After that, the spacecraft will come down to 150 meters, which is called 'vertical descent'. And then based on inputs from sensors and cameras, the lander will decide whether the place it is hovering above is suitable to land or not. And if the lander finds that place is not suitable, then it may move 60 meters on either side for a safe landing.