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Chandrayaan-2's landing module 'Vikram' was on Wednesday brought closer to the Moon after its orbit was lowered further from where it will begin its final descent to pull off a historic soft-landing on the lunar surface in the early hours of Saturday.
Joined by 60 high school students from across the country, Prime Minister Narendra Modi will be present at the Indian Space Research Organisation centre in Bengaluru to witness live the space feat, said a senior official of the space agency.
A successful landing taking billion dreams to the Moon will make India the fourth country after Russia, the US and China to achieve a soft-landing on the lunar surface.
But it will be the first to launch a mission to the unexplored Moon's south pole.
The nine-second de-orbiting manoeuvre--the second in two days--was executed at 3.42 am using the Lander's on-board propulsion system, the ISRO said in a statement giving the latest update on the Rs 978 crore unmanned moon mission.
"With this manoeuvre the required orbit for the Vikram Lander to commence its descent towards the surface of the Moon is achieved," it added.
The Lander is now in an orbit that would be about 35 km from the lunar surface at its nearest point(perigee) from where it will begin its final descent on to the Moon, it said, adding the orbit was 101 km from the lunar surface at the farthest (apogee).
The Chandrayaan-2 spacecraft continued to orbit the moon at a perigee of 96 km and apogee of 125 km.
"Both the Orbiter and Lander are healthy," the ISRO said.
It further said the Lander is scheduled for a powered-descent between 1 am and 2 am on September 7, followed by its touchdown between 1.30 am and 2.30 am.
Following the landing, the rover 'Pragyan' will roll out from 'Vikram' between 5.30 am and 6.30 am and carry out experiments on the lunar surface for a period of one lunar day, which is equal to 14 earth days. The main orbiter will continue its mission for a year.
"Chandrayaan 2 is ready to take a billion dreams to the Moon now stronger than ever before," the ISRO had said while announcing the rescheduled date for the launch after the lift-off was aborted on July 15 due to a technical snag.
A week later, India's Geosynchronous Satellite Launch Vehicle, GSLV MkIII-M1 successfully put the 3,840-kg Chandrayaan-2 spacecraft into the earth's orbit on July 22.
ISRO Chairman K Sivan said the proposed soft-landing on the Moon is going to be a "terrifying" moment as the ISRO has not done it before, whereas Lunar Orbit Insertion (LOI) manoeuvre was successfully carried out during the Chandrayaan-1 mission.
Describing a soft-landing on the Moon, former ISRO chief G Madhavan Nair said it's something like flying saucers coming in hovering on the top and then slowly descending like in science fiction.
It's almost a similar sequence which the ISRO is going to implement, with practically no real-time controls on the ground.
"...Only on-board cameras would look for the right location and once it matches, there are five rocket engines which will precisely control by first reducing the speed and then making it virtually float at that point and have some lateral movement in such a way that it goes just to the location, slowly guide it to the landing site," Nair explained in an interview to PTI.
Cameras, laser ranging systems, on board computers and, above all, software required for the entire operation has to work in unison, said Nair, who spearheaded the Chandrayaan-1 mission more than a decade ago.
"It's a very, very complex operation. I don't think any nation has done a similar operation trying to have real time pictures and then try to have an on-board computer implement autonomously the function of the landing.
"It's going to be a remarkable event and we are all looking forward to that event. I am sure it will be a 100 per cent success," he said.
To increase awareness about its space programmes, the ISRO had in August conducted an online quiz for students from Class 8 to 10.
The space agency selected the top 60 students to witness the historic event.
"Two top scoring Students (from class 8 - 10 only) from each State and Union Territory will be invited to ISRO, Bengaluru Centre to watch the landing of Chandrayaan-2 on the Moon, live along with the Honourable Prime Minister Narendra Modi," according to the terms and conditions of the quiz on the MyGov.in, an innovative platform to build a partnership between Citizens and Government with the help of technology for growth and development of India.
Chandrayaan-2 began its journey towards the moon leaving the Earth's orbit in the dark hours on August 14, after a crucial manoeuvre called Trans Lunar Insertion (TLI) that was carried out by ISRO to place the spacecraft on 'Lunar Transfer Trajectory'.
In a major milestone for India's second Moon mission, the Chandrayaan-2 had successfully entered the lunar orbit on August 20 by performing LOI manoeuvre.
The orbiter carries eight scientific payloads for mapping the lunar surface and study the exosphere (outer atmosphere) of the Moon while the lander carries three scientific payloads to conduct surface and subsurface science experiments.
The rover carries two payloads to enhance the understanding of the lunar surface.
The expedition would also shed light on a completely unexplored section of the Moon, its South Polar region.
According to the ISRO, the objective of Chandrayaan-2 is to develop and demonstrate the key technologies for end-to-end lunar mission capability, including soft-landing and roving on the lunar surface.
On the science front, the mission aims to further expand the knowledge about the moon through a detailed study of its topography, mineralogy, surface chemical composition, thermo-physical characteristics and atmosphere, leading to a better understanding of the origin and evolution of the moon, it said.