Chandrayaan-2: Now, for the most critical phases

Isro released a video of the GSLV Mk III launch vehicle's S200 Solid Rocket Boosters getting ignited and separating. The video was shot from Chandrayaan-2 onboard camera. Photo: ISRO

As the euphoria over Monday’s successful launch of Chandrayaan-2 settles down, the Indian Space Research Organisation (Isro)’s focus has shifted to the more serious business of perfecting the spacecraft’s 23-day earth-bound phase and beyond.

On Tuesday, Isro asserted that India’s most ambitious moon mission is in good health and moving in the right direction. This implies, the initial phases of the eventual lunar landing on September 7 have gone perfectly.

But critical challenges remain. The mission will first have to progressively get into larger orbits around the earth. Every subsequent orbit will bring the Chandrayaan-2 that much closer to the moon’s orbit.

The orbits will be made larger through five “orbit-raising” manoeuvres, propelled by the spacecraft’s onboard engines. Isro has set a deadline of August 13 to complete this phase. When the final orbit reaches about 1.05 lakh km from the Earth’s surface, Chandrayaan-2 will be all set for its lunar transfer.

Dubbed Trans Lunar Injection (TLI), this critical manoeuvre on August 13 or 14 will push the spacecraft onto the moon-bound path, eventually arriving close to the lunar orbit in a week. This week-long transfer follows a Lunar Transfer Trajectory (LTT), when the spacecraft breaks out of the earth’s orbit travelling a distance of 3.84 lakh km.

At the end of this trajectory on August 20 or 21, Chandrayaan-2 will clearly be in the moon orbit’s influence. The spacecraft will be ready for Lunar Orbit Insertion (LOI), before a 13-day Lunar Bound Phase (LBN) begins. During this phase, the mission will get closer and closer to the lunar surface after every orbit.

Once the lander, Vikram, separates from the orbiter at a height of 100 km above the moon’s surface, the orbiter will be on its own, going around the moon for a year. After four orbits, Vikram will be all set on September 7 to undertake the most critical powered descent and landing phase.

Isro chairman K Sivan has dubbed this final landing phase from a height of 30 km the most terrifying 15 minutes of the mission. Isro has never done this planned soft-landing sequence before. The lander will have to touch down at a flat surface on the lunar South Pole for the rover, Pragyaan to roll out and create history.

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