ISRO is attempting to land Chandrayaan 3 on the Moon four years after its predecessor crashed on the lunar surface
On Sept 7, 2019, Chandrayaan 2's 'Vikram' lander descended to around 2 km above the Moon's surface.
Subsequently, the lander lost contact with ISRO, suggesting that it had crashed.
ISRO later said that engines meant to reduce the lander's velocity actually created too much thrust, and small errors accumulated over time.
The lander couldn't turn fast enough to compensate for these errors.
To add to the problems, the landing site chosen by ISRO was too small, and the lander kept accelerating to reach the site even though it was close to the Moon's surface.
Chandrayaan-3 is a follow-on mission to Chandrayaan-2 and its objectives are to demonstrate safe and soft-landing on the lunar surface, roving on the Moon, and to conduct in-situ scientific experiments.
Chandrayaan-2 had failed in its lunar phase when its lander 'Vikram' crashed into the surface of the Moon following anomalies in the braking system in the lander while attempting a touchdown on September 7, 2019. Chandrayaan's maiden mission was in 2008.
The Rs 600 crore Chandrayaan-3 mission was launched on July 14 onboard Launch Vehicle Mark-III (LVM-3) rocket, for a 41-day voyage to reach near the lunar south pole.
The soft-landing is being attempted days after Russia's Luna-25 spacecraft crashed into the Moon after spinning out of control.
After the second and final deboosting operation on August 20, the LM is placed in a 25 km x 134 km orbit around the Moon.
The module would undergo internal checks and await the sun-rise at the designated landing site, ISRO has said, adding that the powered descent -- to achieve soft-landing on the Moon's surface -- is expected to be initiated at around 5:45 pm on Wednesday.
Also watch: Chandrayaan 3 landing: How ISRO changed design after 2nd Moon mission's lander failure
The critical process of soft-landing has been dubbed by many including ISRO officials as "17 minutes of terror", with the entire process being autonomous when the lander has to fire its engines at the right times and altitudes, use the right amount of fuel, and scan of the lunar surface for any obstacles or hills or craters before finally touching down.