Chandrayaan-2: How will Vikram locate precise landing spot near Lunar South pole

Bengaluru, Sep 06: Of all the phases in India's ambitious Moon mission Chandrayaan-2, the final stages of Vikram lander's soft landing on lunar surface would be most challenging for ISRO.

Launching a craft to orbit around moon is not new for ISRO as it was achieved in Chandrayaan-1 itself. In fact the Indian Space agency went beyond Moon and sent an orbiter to Mars.

Soft landing a probe on lunar surface is something that ISRO is doing for the first time. Vikram lander's soft landing on lunar surface is the most critical, complex and challenging phase of the entire
Chandrayaan 2 mission. Even ISRO Chairman K Sivan has acknowledged that the last 15 mins of soft-landing would be tense as it is something ISRO has not done before. This will be the first time that
Indian scientists will attempt a soft landing on the moon, a feat achieved so far by only the US, Russia and China.

Moon-landing process will be comprised of a series of critical and crucial maneuvers. The Lander Vikram has a unique four-legged design.

Vikram weighs 1,471 Kg and has an additional 27 Kg Pragyan rover housed in it. The lander separated from the orbiter on September 2 and entered an orbit of 100 km x 30 km. After a series of braking
manoeuvres, lander's orbit was lowered to 35 km x 97 km. On September 7, at 1.40 am IST, the lander will start performing powered descent.

From here, the Lander's onboard rocket thrust mechanism would be used in a highly controlled manner. For it to be a success, systems like navigation, guidance, controls, propulsion, sensors and various other things have to work in a precise coordinated manner. Braking the speed of the lander 30 km above till landing on the surface will take about 15 minutes.

The lander will have five 800N Liquid thruster engines, touchdown sensors and solar panels. First, all five 800 N engines on the Vikram lander will fire in tandem to decelerate the craft. They will keep
firing until the craft is just a few meters above the lunar surface and settled into a slow, steady approach. The Lander Position Detection Camera will be switched on to identify the perfect place to
land safely on the ground. At this hovering stage of lander, about 400 metres above the moon surface, two engines will be ignited.

The entire descent stage is fully autonomous. It involves the onboard computer taking continuous input from sensors about its distance, velocity, acceleration, orientation, etc., computing its trajectory and auto-correcting it by orchestrating firing of the engines, until a safe touchdown. At an altitude of 10 metres, the ISRO will carry out the landers parabolic descent for soft landing by igniting the central

engine and using the touchdown sensor at the bottom of the stand.

Hours after touchdown, rover Pragyaan will roll out from inside the lander and carry out probe of the lunar soil.