Prime Minister Narendra Modi watches on a screen the successful launch of Chandrayaan-2 by GSLV MkIII-M1 vehicle from Satish Dhawan Space Centre of Sriharikota, in New Delhi on Monday | pti
Prime Minister Narendra Modi watches on a screen the successful launch of Chandrayaan-2 by GSLV MkIII-M1 vehicle from Satish Dhawan Space Centre of Sriharikota, in New Delhi on Monday | pti

Chandrayaan-2: India over the moon

The 48-day journey to moon’s southern polar region begins as GSLV-MkIII successfully launches Chandrayaan-2 in earth’s orbit; delay results in adoption of a longer route

SRIHARIKOTA: India was ‘over the moon’ on Monday as GSLV-MkIII, in its very first operational flight, launched Chandrayaan-2 spacecraft into the designated earth orbit. The spacecraft, weighing 3,850 kilograms, has begun its 48-day ‘gruelling’ journey to the moon, which is prone to be riddled with challenges.

The move, experts say, has put India on course for the next big phase in space exploration. Though India’s lander ‘Vikram’ will be soft-landing on moon 56 years after Soviet Union’s Luna 9, this is a mission like none before. For, it will shed light on a completely unexplored section of the moon, the South Polar region. 

As the entire world watched, the 43-metre tall ‘Bahubali’ rocket blasted off from the second launch pad in Sriharikota at 2.43 pm. Tension in the mission control room was palpable as the 640-tonne rocket took off, considering that the first attempt had to be called off due to a technical snag, about a week ago. Another delay would have resulted in the mission being suspended till September.

Chairman K Sivan said the success was sweeter as it had come after a ‘fallout’ and serious technical glitch. “ISRO bounced back with flying colours,” he said announcing the successful launch. “It’s the beginning of a historic journey of India towards the moon.” He said the amount of work done in 24 hours following the technical snag was mind boggling.       

“The vehicle was brought back to normal... root cause of the technical snag was identified and corrected. Everything happened in 24 hours. In the next one-and-half days, required tests were conducted to ensure the corrections made were proper, in the right direction,” Sivan said.  

“The expert team constituted was on the job for the last seven days, to ensure every system functions properly. It’s my duty to salute all of them.” 

Minor Detour 

The distance to moon is 3.84 lakh kilometres. Ensuring trajectory accuracy while covering such a large distance poses many challenges as the flight path is influenced by factors, such as the non-uniform gravity of earth and moon, the gravitational pull of other astronomical bodies, solar radiation pressure and moon’s true orbital motion. 

The mission sequence has been reworked to ensure the lander gets to moon by September 6 or 7. This is to ensure that it breathes for full 14 Earth Days and performs in-situ measurements near the landing site. The path it takes, however, may differ. This is because the duration between launch and landing has been narrowed down to 48 days from 54 days as was originally planned. The delay has increased the travel distance by 6,000 kilometres. 

As per the revised schedule, Chandrayaan-2 will spend 23 days in Earth’s orbit instead of 17. It will raise its orbit in this period and begin the voyage towards the moon, which will take another seven days. For the next 13 days, it will remain in the lunar orbit, taking slingshots around the moon, in an orbit of 100 km. 

Earlier, it was supposed to spend 28 days in the lunar orbit. The lander will separate from the orbiter on Day 43 (September 2) and continue to hang  around the moon for another few days in a lower orbit. The actual landing would happen on September 6-7. In the next 48 days, the Chandrayaan-2 mission team would conduct 15 key manoeuvres.

Heavy duty

The actual showpiece on Monday was the launch vehicle, GSLV MkIII. ISRO has customized the rocket and made several modifications to accommodate 500 kg of additional payload for the mission. 
One of the modifications was to replace liquid engine thrust with High Thrust Vikas Engine, says S Somnath, director of Vikram Sarabhai Space Centre.  
“Also, burn to depletion strategy in cryogenic stage was adopted. We did a process change to extract total liquid oxygen which maximises the payload. We have also conducted inner mass reduction. All this contributed to increase in payload capacity by 500 kg.”

15 minutes of ‘terror’

Sivan has described the last 15 minutes before landing as ‘terror’. The most challenging part of the mission is soft-landing, which is divided into ‘rough braking’ and ‘fine braking’. “Variation in local gravity has to be factored into the lunar descent trajectory. The on-board Navigation and Control (NGC) and propulsion system has to work in unison, autonomously and automatically for a successful landing. Further, the landing site landscape features should not result in a communication shadow area,” ISRO said.  

The renewed global interest in moon is because of its rich reserves of water and helium-3.
As the Chandrayaan-2 approaches the Moon, on-board thrusters fire precisely to reduce its velocity for lunar capture. The margin of error in this calculation and maneuvers is very narrow. The lander and rover should also deal with extreme temperature and vacuum. 

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