Chandrayaan-2's landing module 'Vikram' would begin its final descent in the direction of pulling off a historic soft landing on the lunar surface in the early hours of Saturday, 7th September 2019, as the Indian Space Research Organization anticipates with bated breath for the "terrifying moment".
A successful landing would make India the 4th country after Russia, the US and China to achieve a soft landing on the moon. But it is going to be the 1st to launch a mission to the unexplored lunar South Pole.
On Monday, the 1,471 kg lander successfully has been separated from the orbiter and started revolving around the Moon, by lowering its orbit over two manoeuvres as well as performing several pre-landing tests.
Vikram' with rover 'Pragyaan' housed inside is planned for a powered-descent between 1 am and 2 am on 7th September, followed by its touchdown between 1.30 am and 2.30 am. The lander is at present is in an orbit that would be approximate as per reports 35 km from the lunar surface at its nearest point from where it would begin its final descent.
ISRO has stated that Chandrayaan-2 would attempt to soft-land the lander as well as a rover in a high plain amid two craters, Manzinus C and Simpelius N, at a latitude of about 70 south. The chairman of ISRO has stated that the proposed soft landing on the Moon is going to be a "terrifying" moment since ISRO has not done it before, where Lunar Orbit Insertion (LOI) manoeuvre has been successfully carried out during the Chandrayaan-1 mission.
Furthermore, of the 38 attempts of 'soft landing' on the lunar surface so far, only 20 were successful. Just a few months back, Israel's effort has crash-landed on the moon. If everything goes as per the plan on Saturday morning, India would become the 4th country after Russia, the US and China to achieve success.
ISRO has explained the landing manoeuvres, that once the manoeuvre starts from about 30 km to land on the surface of the moon, it would take 15 minutes. This particular 15 minutes travel of lander is new to ISRO. It is for the first time ISRO is going to another body where there is no atmosphere and using the propulsion system ISRO would have to break the velocity and bring the vehicle safely to soft-land. To achieve this there must be a balance between the gravity and thrust. For that modulation of the thrust of the engine is needed. Following the landing, the rover 'Pragyaan' would roll out from 'Vikram' between 5.30 am and 6.30 am.
While, the 'Pragyaan' is going to carry out experiments on the lunar surface for a period of one lunar day, which is equal to 14 earth days, the main orbiter shall continue its mission for a year. The lander, as well as rover, carries country's symbols on them, which would remain on the moon for long.
The rover has 6 wheels (3 each on both sides), the back 2 wheels- one has Ashoka Chakra on it and the other has ISRO emblem. Furthermore, the ramp of the lander on which rover would come out and land on the moon has an Indian flag on it.
The Rs 978 crore unmanned moon mission is expected to put some light on a completely unexplored section of the Moon that is its South Polar Region.
As per ISRO, the lunar South Pole is particularly interesting because of the lunar surface area there that remains in shadow is much larger than that at the North Pole and there was a likelihood of the presence of water in permanently shadowed areas around it.
Also, the South Pole region had craters that are "cold traps" and comprise a fossil record of the early Solar System. The 3,840-kg Chandrayaan-2 spacecraft has been launched into the earth's orbit by India's Geosynchronous Satellite Launch Vehicle, GSLV MkIII-M1, on 22nd July
Chandrayaan-2 satellite started its journey towards the moon leaving the earth's orbit in the dark hours on 14th August, after a crucial manoeuvre called Trans Lunar Insertion (TLI) that has been carried out by ISRO to place the spacecraft on "Lunar Transfer Trajectory".
The spacecraft effectively entered the lunar orbit on 20th August through performing Lunar Orbit Insertion (LOI) manoeuvre. On 2nd September, the lander 'Vikram' has been successfully separated from the orbiter, following which two de-orbiting manoeuvres were executed to bring the lander closer to the Moon.
The orbiter carries 8 scientific payloads for mapping the lunar surface as well as studies the exosphere (outer atmosphere) of the Moon whereas the lander carries 3 scientific payloads to conduct surface and subsurface science experiments.
The rover carries 2 payloads towards enhancing the understanding of the lunar surface. The rover would be rowing on the moon on its own propulsion at the speed of 1 cm per second and would cover 500 metres in its lifetime.
Why the last 15 minutes of lander Vikram are most crucial in Chandrayaan-2 landing?
The question is what shall happen in the last 15 minutes before touchdown?
At 1:40 am on 7th September, Vikram would begin its descent from a height of 35 km above the lunar surface and a velocity of around 6,000 kmph. In over 10 minutes, the lander shall drop to a height of 7.4 km above the Moon altitude and lower its speed to around 526 kmph.
During this point, things would pick up the pace and every second is going to be very vital. Over the next 38 seconds, the lander shall further reduce its speed to 331.2 kmph and reach a height of 5 km above the lunar surface. As it drops towards an altitude to 400 metres above the lunar surface during the following 1.5 minutes, Vikram would have to lose more velocity and reach a speed of around 100 kmph. During this point, it would briefly suspend its descent and hover for approximately 12 seconds to collect data of the lunar surface.
Touchdown is less than 3 minutes away at this point. While Vikram resumes its descent, it would drop 300 mts in the span of 66 seconds and once again hovering at the height of 100 mts above the lunar surface. This pause of approximately 25 seconds is to give the lender a chance to make a final choice amid two pre-determined landing sites. The onboard instruments would give it the necessary information to make this decision - the lander carries 3 scientific payloads to carry out surface and subsurface science experiments.
If Vikram selects the first site, the lander would make a vertical descent to a height of 10 mts above the lunar surface over 65 seconds although significantly reducing its velocity.
Alternatively, if it chooses for the second site, it would firstly descend to a height of 60 mts over 40 seconds, and then drop to 10 metres in the next 25 seconds. In both ways, from the height of 10 mts, Vikram would take just 13 seconds to expectantly make history and soft-land on the moon. From 15 minutes after the touchdown, Vikram is going to send in the first pictures.
Thus, 4 hours after landing, between 5.30 am and 6.30 am, the Pragyaan rover would be unloaded from the Vikram lander. The 6 wheeled robotic vehicles with a mass of 27 kg shall then conduct surface and sub-surface experiments for 1 lunar day, which is equivalent to around 14 Earth days. It could travel at a speed of 1 cm per second as well as leverages solar energy for its functioning. It would cover 500 metres in its lifetime.
Conclusion:
As said by ISRO, the objective of the mission Chandrayaan-2 was to develop as well as establish the main technologies for end-to-end lunar mission competence, which includes soft-landing and roving on the lunar surface.
Considering the science part, the mission purposes is to furthermore develop the understanding of the moon through a comprehensive study of its landscape, mineralogy, surface chemical composition, thermo-physical characteristics as well as atmosphere, leading towards improved knowledge of the origin as well as the evolution of the moon.
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