Chandrayaan-2’s Vikram to land near Moon’s south pole on Sept 6

Chandrayaan-2 will be launched from the Second Launch Pad at 2.51 am early Monday next from the spaceport of Sriharikota by the heaviest home grown rocket, three-stage Geosynchronous Satellite Launch Vehicle Mark-III (GSLV Mk-III), capable of launching 4-ton class of satellites to the Geosynchronous Transfer Orbit (GTO).

Weighing 3,840 kg, Chandrayaan-2 is on a mission unlike any before. Leveraging nearly a decade of scientific research and engineering development, the second lunar expedition will shed light on a completely unexplored section of the Moon--its South Polar region, a site not explored by any country yet, ISRO sources said. Only Russia, the United States and China have soft-landed on the moon.

Ahead of the launch, a full dress rehearsal of the launch was conducted at the SHAR Range. After its launch, Chandrayaan-2 will be injected into an earth parking 170 x 40,400 km orbit.

A series of maneuvers will be carried out to raise its orbit and put Chandrayaan-2 on Lunar Transfer Trajectory. On entering Moon’s sphere of influence, on-board thrusters will slow down the spacecraft for Lunar Capture.

The Orbit of Chandrayaan-2 around the moon will be circularized to 100x100 km orbit through a series of orbitalmaneuvers.

On the day of landing, the lander will separate from the Orbiter and then perform a series of complex maneuvers comprising of rough braking and fine braking. Imaging of the landing site region prior to landing will be done for finding safe and hazard-free zones.

The lander-Vikram will finally land near South Pole of the moon on September 6 and subsequently, Rover will roll out and carry out experiments on Lunar surface for a period of one Lunar day which is equal to 14 Earth days. The Orbiter will continue its mission for a duration of one year.

Chandrayaan-2 has several science payloads to expand the lunar scientific knowledge through detailed study of topography, seismography, mineral identification and distribution, surface chemical composition, thermo-physical characteristics of top soil and composition of the tenuous lunar atmosphere, leading to a new understanding of the origin and evolution of the Moon.

The Orbiter payloads will conduct remote-sensing observations from a 100 km, orbit while the Lander and Rover payloads will perform in-situ measurements near the landing site.

Other key payloads included Chandrayaan 2 Large Area Soft X-ray Spectrometer for Elemental composition of the Moon, Imaging IR Spectrometer for Mineralogy mapping and water-ice confirmation, Synthetic Aperture Radar L and S Band for Polar-region mapping and sub-surface water-ice confirmation, Orbiter High Resolution Camera for High-resolution topography mapping, Chandra’s Surface

Thermo-physical Experiment for Thermal conductivity andtemperature gradient, Alpha Particle X-ray Spectrometer and LaserInduced Breakdown Spectroscope for In-situ elemental analysis and abundance in the vicinityof landing site.

As ISRO is gearing up for the second lunar mission, there were several challenges involved in a moon landing. First and foremost was accuracy in trajectory as the distance to the moon was approximately 3.844 lakh km. Ensuring trajectory accuracy while navigating such a large distance poses many challenges as trajectory was influenced by the non-uniform gravity of the earth and the moon, gravitational pull of other astronomical bodies, solar radiation pressure and the Moon’s true orbital motion, ISRO said in its website.

Owing to the large distance from earth and limited on-board power, radio signals used for communication are weak with heavy background noise, which needs to be picked up by large antennas.

Chandrayaan-2 will perform a series of TLI burns for raising its apogee successfully to reach the vicinity of the Moon’s orbit. As the Moon’s location is continually 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 calculations and manoeuvres is very narrow.

Lunar gravity is ‘lumpy’ due to uneven mass distribution under its surface. This influences the orbit of the spacecraft. Also precise knowledge of the thermal environment at orbital altitude is essential for keeping on-board electronics safe.

This is the most challenging part of the mission and is divided into ‘rough braking’ and ‘fine braking’. Variation in local gravity has to be factored into the lunar descent trajectory. The on-board 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.

The lunar surface is covered with craters, rocks and dust. Firing of on-board engines close to the lunar surface results in backward flow of hot gases along with dust. Lunar dust is miniscule and is hard, barbed and jagged. Its negative charge makes it stick to most surfaces, causing a disruption in deployment mechanisms, solar panel performance and NGC sensorperformance.

A lunar day or night lasts 14 earth days. This results in extreme surface temperature variations. Moreover, the ambient pressure of lunar surface is a hard vacuum. This makes the lunar surface an extremely hostile environment for lander and roveroperations.