SRIHARIKOTA (Andhra Pradesh): India is on course to create history and commence a next big phase in space exploration. Though an Indian lander - Vikram - is attempting to soft-land 56 years after Soviet Union's Luna 9 (1966), Chandrayaan-2 is on a mission unlike any before and would shed light on a completely unexplored section of the Moon - South Polar region. Rich reserves of water and helium-3 are the biggest driving forces globally for renewed interest in moon.
First things first. In its very first operational flight, GSLV-MkIII has successfully launched Chandrayaan-2 spacecraft, weighing 3,850 kg, into the designated earth orbit, which was just the beginning of a long grueling 48-day journey that is riddled with several challenges.
As the world watched, the 43 metres tall Bahubali rocket with a lift-off mass of 640 tonnes has blasted-off from the second launch pad at 2.43 pm from Sriharikota. Tension was palpable in the mission control room as the first attempt, a week ago, had to be called-off in the eleventh hour due to a technical snag. Another delay would have meant suspending the mission till September.
Congratulating the ISRO team, Chairman K Sivan said the success was double sweeter since it had come after a 'fallout' and serious technical glitch. "ISRO had bounced back with flying colours. I am extremely happy to announce that the GSLV MK-III successfully injected Chandrayaan 2 spacecraft into Earth Orbit. It is the beginning of a historic journey of India towards the moon," Sivan said
He said work done in the 24 hours after technical snag was mind-boggling. "The vehicle was brought back to normal, identified the root cause of the technical snag and corrected it. Everything happened in 24 hrs. In the next one-and-a-half days the required tests were conducted to ensure that the corrections made was proper and in the right direction. In fact, the expert team constituted was on the job for the last seven days to ensure every system functioned properly. It's my duty to salute all of them," ISRO chairman said.
ISRO scientists said the distance to the moon is approximately 3.84 lakh km. Ensuring trajectory accuracy while navigating such a large distance poses many challenges as the flight path is influenced by the non-uniform gravity of the Earth and Moon gravitational pull of other astronomical bodies, solar radiation pressure and the moon's true orbital motion.
ISRO has reworked on mission sequence to ensure lander and rover modules would land on the moon on September 6-7 in order to breathe for full 14 Earth days and perform in-situ measurements near the landing site. But the path it would take may differ, since the gap between launch and landing has been narrowed down to 48 days compared to original 54 days.
As per the revised mission details, Chandrayaan-2 would spend 23 days in the Earth’s orbit instead of 17. After raising its orbit during this period, the spacecraft would begin the voyage towards the Moon, which will take seven days. For the next 13 days, it would remain in lunar orbit, taking slingshots around the Moon in an orbit of 100 km.
Earlier, it was supposed to spend 28 days in lunar orbit.
The lander would separate from the Orbiter on Day 43, or September 2, and could continue to hang around the moon for another few days in a lower orbit. The actual landing would happen on September 6-7.
15 key maneuvers, 15 minutes of terror
Sivan said, in next 48 days, the Chandrayaan-2 mission team who took over the controls would conduct 15 key maneuvers and 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.
Chandrayaan-2 will perform a series of Trans Lunar Injection (TLI) and Lunar Capture for raising its apogee successively to reach the vicinity of the Moon's orbit. As the Moon's location is continuously changing due to orbital motion, the intersection of Chandrayaan-2 and the Moon's path has to be predicted sufficiently in advance with a high level of accuracy. As the Moon approaches the apogee of Chandrayaan-2, on board thrusters fire precisely to reduce its velocity for lunar capture. The margin of error in these calculation and maneuvers is very narrow.
The lander and rover should also deal with extreme temperature and vacuum. "A lunar day or nigh lasts 14 Earth days. This results in extreme surface temperature variations. Moreover, the ambient pressure of the lunar surface is a hard vacuum. This makes the lunar surface an extremely hostile environment for lander and rover operations," ISRO officials explained.