1. US, Russia and China have all landed spacecraft on the moon between +/-30 degrees of the lunar equator. This is much easier as slight deviations in orbit angle do not matter.
India is landing near the lunar South Pole at 79 degree south. This is much more difficult as it needs an exact 90 degree orbit.
2. The lunar South Pole is critical to establishing a colony on the moon since it is likely to have water. The lander and the rover will search for this water. This data will be acquired by Nasa for their lunar colony mission. The data has been calibrated accordingly.
3. The landing will happen on a surface with a 12 degree incline between two craters. This patch has less rocks. Missing this landing point will cause the lander to topple over as other surfaces have sharp undulations and rocks. An image of this patch has been stored in the lander and it will locate the patch not only through inertial navigation but also by image comparison. This is the first time such a technology is being used in space landing.
4. The lander will have four thrusters at the four corners of the lander and a central thruster. Each thruster will be separately controlled using AI to ensure a vertical landing. Once again this technology of differential thrusters is being used for the first time in space landing.
5. At a height of 13 meters from the lunar surface, the four corner thrusters will be shut off and only the central thruster will work. This thruster will push the dust away from the lander. In other landings by other countries, dust has been a major problem destabilising the lander and damaging instrumentation and communication system. Once again, such a dust minimised landing environment will be a global first.
6. To establish the height of the lander very accurately over the moon’s surface, in addition to the usual inertial navigation system, an altimeter of the type in an aircraft will be used to have a cross check.
7. The Chandrayaan and the lander will both be generating data independently on speed, height, temperature etc. and the cross referencing of the data will provide additional validation of system health. This technique is also a first.
In addition to the above seven firsts, some other interesting points are:
a) The landing will happen on 7th September which is the beginning of the lunar day. The experiments will continue for the next 14 earth days which is the length of one lunar day.
It is important to land at the beginning of the lunar day as this gives a 14 day window.
b) The lander and rover will then move into the lunar night. As the solar panels will not work, no experimentation will be possible.
c) The temperature will slowly drop to minus 200 degree C and the lander and the rover instrumentation may not survive such low temperatures.
d) If the lander and rover survive the first lunar night they will again come alive in the lunar day and another 14 earth day experimentation window will open up.
e) Expetiments will cover surface conditions, below surface conditions, temperature gradients, presence of eight specific elements including calcium and magnesium, rock structure and minerals and the all important Water.
f) Experiments involve spectrometry, thermal measurements, rock hardness measurements and so on.
g) Lander will drill in, rover will roam around in a 500 meter radius.
h) Rover has AI but will be controlled by the lander. The lander will communicate with ISRO stations.
i) Once the landing process has been initiated there will be no earth based interventions. The lander and rover will be on their own.
The mission is very complex. I have left out the orbital and velocity reduction details and concentrated on the landing. Only 37% of the soft landing attempts of different nations have been successful. ISRO is confident.
*Let us wish the ISRO team all success.*
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