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Chandrayaan-2 Mission: The Last Mile Remains

Dr Ajey Lele

6 September 2019 New Delhi

Chandrayaan-2, India’s second mission to the Moon, is making remarkable progress. On 7 September 2019, the mission will go through its most difficult part—soft-landing on the Moon’s surface. The soft landing would be of the Lander (with a Rover inside its belly) unit of Chandrayaan-2. The entire mission has two major parts: the Orbiter that could be described as a satellite and the Lander-Rover system. The Orbiter is a 2,379 kg satellite with a power of 1000W and has eight important sensors on board. The Vikram Lander weighs 1,471 kg and the Pragyan Rover weighs 27 kg. The designed life of the Orbiter is one year. It will photograph the Moon’s surface from a height of 100 km. The Lander-Rover system would be positioned on the Moon’s surface for ground observations and will operate for 14 earth days (equivalent to one lunar day).

The 48-day journey to the Moon began on 22 July 2019. A major milestone for this mission was achieved on 2 September 2019 when the Vikram Lander with Pragyan Rover in its belly, separated from the ‘mothership’ Orbiter. The Orbiter has reached close to its planned location, which is an orbit of around 100 km above the Moon’s surface. The Vikram Lander has begun its journey to the Moon’s surface with the soft landing planned for September 7. Controlled landing on the Moon’s surface is going to be a major challenge. The landing site has already been identified. There are various challenges associated with this process, the main being the correct reduction of the velocity to 2 metre/second before landing while ensuring no major jerks that could damage the system.

The Moon is the Earth’s natural satellite 386,400 kilometres away. The world celebrated 50 years of the Apollo 11 mission in July, marking the day when history was made with Neil Armstrong and Buzz Aldrin becoming the first humans to walk on the Moon. That mission began on 16 July 1969, and reached the lunar orbit in just 51 hours and 49 minutes. This was made possible by a very powerful rocket called Saturn V, a multi-stage rocket. Obviously, the first question which comes to mind is ‘why five decades after the first human flight to the Moon, India is taking so much time to reach the Moon and that too for an unmanned mission’?

The simple answer is that India does not have a powerful enough rocket like the Saturn V. India’s indigenous GSLV rocket has major design limitations and cannot carry much of weight (this mission is 3.8 tonnes in total weight). However, innovation has been the key to ISRO’s success and it is important to note that ISRO’s earlier missions, such as Chandrayaan-1 and even the Mangalyaan mission to Mars, were undertaken with a less powerful rocket called PSLV (Polar Satellite Launch Vehicle). Interestingly, the slowest mission to the Moon till date has been the European space agency’s SMART-1 probe. Launched in 2004, it took one year, one month and two weeks’ to reach the Moon. However, technologically it is considered the most advanced mission. In contrast, China’s Chang’e 3 mission (during 2013) took hardly five days to reach the Moon. However, China follows a different format for launch and their latest mission Chang’e 4 is a good example of this. The relay satellite for Chang’e 4 was launched on 20 May 2018 while the Lander-Rover mission was launched on 7 December 2018 and it soft-landed on the Moon on 3 January 2019.

It could be argued that it’s not the time factor but the cost factor which is more important. Truly, no two missions should be compared because every mission would have its specific purpose and instrumentation (hence the weight of the mission) and duration of the mission would be planned accordingly. However, it has been observed that ISRO runs among the most cost-effective space programmes and this is the case with Chandrayaan-2.

An ongoing Moon mission is China’s fourth, Chang’e 4. The rover for this mission, the Yutu-2, has taken good amount of observations during its travel on the Moon surface. Yutu-2 is 140 kg system (Pragyan Rover weighs just 27 kg) and has a designed life of three months (say four lunar Days). So it is clearly working beyond the designed life. As of mid-August 2019, Yutu-2 had covered a distance of 271 metres (over 800 feet) on the Moon’s surface. It’s a difficult task for any rover to move on the Moon. ISRO’s proposal for Pragyan to travel a distance of 500 metres (1,640 feet) in one lunar day looks very ambitious. ISRO’s calculation could be that since Pragyan’s weight is far less, it will be able to cover that distance.

Yutu-2 is presently exploring one of the lesser-known areas of the Moon, its far side, which faces away from the Earth. Yutu-2 has found some evidence about minerals. One of the most interesting findings is an oddly coloured “gel-like” substance of unknown origin. This discovery took place on Lunar Day 8 (that began on 25 July 2019). It is too early to draw any conclusions from this finding. Pragyan is also expected to bring in some new knowledge about the south polar region of the Moon.

Chandrayaan-2 has in total 13 sensors and in addition there is one sensor from NASA. Eight sensors are placed on the Orbiter which will gather data that will help scientists better understand the Moon and its mineral composition. All this data will help develop a three-dimensional map of the Moon’s surface. The Lander’s three sensors will analyse the surface and sub-surface temperature of the landing site and make a seismological assessment. The two sensors on board the Rover would help understand the nature and composition of the surface on which the Rover would be moving.

As of 3 September 2019, the first de-orbiting manoeuvre for Chandrayaan-2 has been performed successfully. Let us hope that years of efforts by ISRO scientists will bear fruit on 7 September with a successful soft-landing on the Moon’s surface.

(The author is a Senior Fellow, Institute for Defence Studies and Analyses, IDSA, New Delhi. Views expressed in this article are personal.))

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