Uppdatering
https://www.isro.gov.in/update/03-jun-2019/challenges-of-moon-landing
The challenges of a Moon landing
Trajectory Accuracy
The distance to the Moon is approximately 3.844 lakh km. Ensuring trajectory accuracy while navigating such a large distance poses many challenges as trajectory is influenced by the non-uniform gravity of the Earth and Moon, gravitational pull of other astronomical bodies, solar radiation pressure, and the Moons true orbital motion.
Deep-space Communication
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.
Trans Lunar Injection (TLI) and Lunar Capture
Chandryaan 2 will perform a series of TLI burns for raising its apogee successively 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.
Orbiting Around the Moon
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.
Soft Landing on the Moon
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 onboard 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.
Lunar Dust
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 sensor performance.
Extreme Temperatures and Vacuum
A lunar day or night 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.
