Chandrayaan-2 Moon landing on Sept 7, 1.55 am

Flawlessly clearing 30 'heart-stopping' minutes of Chandrayaan-2's critical Lunar Orbit Insertion (LOI), the Mission's grand finale is now in sight: Soft-landing on the lunar surface at 1.55 am on September 7, a task never attempted before by the Indian Space Research Organisation (Isro).

But before embarking on the final 'terrifying 15 minutes' of descent, as Isro Chairman K Sivan reiterated on Tuesday, Chandrayaan-2 will undertake four more key maneouvres. These 'lunar burns' will be carried out on August 21, 28, 30 and September 1 to place the spacecraft in progressively lower orbits.

By September 1, Sivan explained, the spacecraft would have descended from the 114 km X 18,000 km orbit immediately after LOI to settle in a 100 km X 100 km orbit around the Moon. This will be the Orbiter's final resting place, going around the Moon for well over a year.

Like a bride's separation

On September 2, the Lander, Vikram will separate from the Orbiter. “Entire attention of the mission team will shift to the Lander that day. It would be like the bride separating from her parental home,” said Sivan in mirth.

The next day, a short Retro De-Orbit maneouvre will be conducted to ensure normalcy, before the Lander, Vikram moves down to a 35 km X 97 km orbit. “Over the next three days, various parameters of Vikram will be checked and rechecked.”

Isro's most complex operation till date, the Lander's final powered descent will start precisely at 1.40 am on September 7. Once it descends to an altitude of about 400m, Vikram will hover for 12 seconds to capture images of the landing surface.

This would be critical, reminded Sivan. “The surface should be flat with a slope of less than 12 Degrees. Anything beyond that, the Lander will topple over.”

Moon dust challenge

To ensure that the touchdown is safe and soft, all fire engines aboard Vikram will be fired to reduce the velocity. The final 10m descent will be achieved in 25 seconds.

But touching down with multiple engines firing could trigger moon dust, a major concern for any Moon-landing mission. “To avoid this, at a height of 13m, the four corner thrusters will be switched off. Only the single engine in the centre will be on. This way, the dust will scatter horizontally,” Sivan explained.

Three hours after touchdown, the Rover's solar panels will be deployed, and three hours, 15 minutes later, the Rover will begin to move. “Moving at 1 centimetre per second, the Rover will cover about 500m in one lunar day, equivalent to 14 Earth days.”