Indian Space Research Organisation’s (ISRO) Chandrayaan-2 is all set to land on the Moon on September 7. The soft landing of Chandrayaan-2 Vikram Lander is scheduled on the surface of the Moon between 1:30 am and 2:30 am on September 7, after the second de-orbiting maneuver was successfully performed on Wednesday, September 4. Ahead of the historic landing, Republic World spoke to Professor Mayank Vahia, Dean, School of Mathematical Sciences, NMIMS, and Formerly at Department of Astronomy & Astrophysics at Tata Institute of Fundamental Research (TIFR). Professor Vahia answered various questions about the mission and explained the complex procedures in a simplified manner.
ISRO has been constantly giving updates, earlier it was about the orbit raising maneuvers and since Chandrayaan-2 is reaching the Moon, it has been about the orbit lowering maneuvers. Prof. Vahia uncluttered the gravitational technicalities behind 'maneuvers' and how ISRO goes about performing them. He said, “There are two or three things about it. The first issue is that, when Chandrayaan-2 was launched, it was moving very fast. If it would have continued to move in the same rapid way, it would have eventually overshot the Moon. So as it neared the Moon, it had to be slowed down so that it got caught up in the Moon’s orbit but, if slowed down too much, then it would have crashed on the lunar surface. There has to be a critical speed which is strictly sensitive to the height above the Moon in order to be captured by its orbit.”
Speaking about the second issue, which is to refine the orbit around the Moon such that a landing can be attempted, he said, “The Chandrayaan-2 got to the Moon by August 20 and it was captured within its orbit but it was highly elliptical and there is nothing much that can be done about such an orbit, so gradually Chandrayaan-2 had to be slowed down until it went through multiple stages and only on September 1, they managed to get the nearly circular 100 km orbit. The problem with that 100 km orbit is that it is so close to the surface of the Moon that even a mountain on the Moon can cause jitters because of the extra gravity above the mountains as compared to a valley.” All these things have to be managed by ISRO so that the orbit remains stationary and stable.
After Chandrayaan-2 is stabilised and it moves in the correct orbit at a correct distance, then Vikram Lander has to be disconnected from it. It had to be brought slightly lower so that it could look at a surface of the Moon especially the South Polar region so that a spot which is ideal for landing can be identified. This is the reason it took ISRO, extra 6 days to get the correct images of the place where it has to land, analyse the 3-D terrain mapping and then decide the final place for Vikram to land. He also highlighted that when the Vikram is orbiting the Moon, it is also scoping the Lunar surface and determining the appropriate spot for landing. Other things which are necessary for a perfect landing is the velocity and accuracy to land within the few metres of the decided spot.