Bengaluru:  As the Chandrayaan-2 Lander prepares to touch down on the lunar surface less than 24 hours from now, the entire mission team has its attention riveted on the final 15 minutes. The final, unprecedented epoch-making descent will commence on Sept. 7 at 1 am.

Prime Minister Narendra Modi will join a massive gathering of scientists, students, space buffs and the media in Bengaluru to witness the historic landing live from the Indian Space Research Organisation (ISRO) Telemetry, Tracking and Command Network (ISTRAC).

For ISRO, the hours leading up to the descent would be a mix of extreme caution, precision and anxiety. A lot will depend on the Orbiter’s onboard cameras focused on identifying the safest landing spot on the South Polar Region of the Moon.

Scientists are now waiting with bated breath and fingers crossed, wishing that the mission’s Lander Vikram makes a perfect landing to achieve the historic first of a spacecraft touching down near the Moon’s South Pole, something that no country has done before.

That’s because of the crucial 15 minutes of powered descent, which ISRO Chairman K. Sivan had described as ‘most terrifying’. Here is why it is terrifying — ISRO scientists will not resort to remote manual control of the Lander while it makes the descent to the lunar surface.

Instead, the Lander Vikram will manage its own landing in an automated mode using its onboard sensors to guide it to the perfect landing spot. These sensors are more sophisticated versions of the reverse gear hazard alert sensors installed in the latest models of cars.

Apart from guiding, the sensors will also help Vikram “choose” the most ideal surface to safely land by linking with its lunar surface scanning and imaging capability as it approaches to make a soft-landing.

“There will be no remote manual commands guiding the Lander from the Earth-based control stations during the crucial 15 minutes as had been done so far,” scientists said, adding that any error on the part of the sensors can lead to a problem.

“This will be made possible as the parameters and commands for the sensors are loaded remotely into the Lander’s system only an hour before the landing begins,” they said. And once the process starts, there is no recalculation or tweaking. ISRO Chief Sivan said that to land on the lunar surface, Vikram will have to reduce its velocity from 1.6km per second to zero in a controlled manner by using its thrusters from 800 metres above the surface.

The landing site will have to be flat. Anything beyond an angle of 12 degrees would be risky as the Lander could topple over and jeopardise the entire mission. If that happens, it could be extremely tough for the Rover, Pragyaan to roll out of Vikram three hours after impact.

Weighing the success rate of such missions, Sivan earlier said, “Soft-landing on moon has a success rate of 37% (globally). However, we have learnt from their failures.” Vikram’s powered descent between 1 am and 2 am will be followed by the actual touchdown any time from 1.30 am to 2.30 am.

On July 22, Rs. 978 crore Chandrayaan-2 Moon Mission lifted off aboard the GSLV-Mk III launcher from the Satish Dhawan Space Centre in Sriharikota. Leaving the Earth’s orbit on Aug. 14, the spacecraft had entered the Lunar orbit six days later.

How and where to watch live

The ISRO website (www.isro.gov.in) will telecast the updates from its control room at the Satellite Control Centre (SCC) in Bengaluru. This stream will also be on the PIB’s YouTube channel. To get minute-by-minute updates, you could also track ISRO’s Twitter handle and Facebook page.