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Chandrayaan-2 to soft land on the Moon on September 7 at 1.55 am

The lander will execute a 15-minute soft landing, and after four hours, the rover will descend on the moon. "Precise execution is important," said ISRO chief K Sivan

August 20, 2019 / 05:53 PM IST

After its launch on July 22, Chandrayaan-2 will do a soft landing on the Moon's South Pole  on September 7 at 1.55 am, K Sivan, chairman, Indian Space Research Organisation announced.

After landing lander and rover will study moon's south pole for one lunar day or 14 earth days

Speaking to media persons, Sivan said, “Today (August 20) Chandrayaan-2 has crossed a major milestone carried out at 9 am for 30 minutes. Chandrayaan-2 was precisely injected in the designated orbit.”

After reaching the milestone of reaching earth's orbit, the next step now is to prepare the vehicle for the soft launch through a series of manoeuvres.

Soft landing refers to landing of a space vehicle on a celestial body (or the earth) in a manner designed as to prevent damage or destruction of the vehicle. If successful, India will join the elite club consisting of the US,Russia and China.

Why is Chandrayaan-2 significant? 

At Rs 1000 crore, the project is one of the most challenging and complex projects ever handled by the space agency. Project assumes even more significance considering that this is the first time a space agency is exploring the lunar South pole, which has water ice permanently shadowed in the area.

"The whole world is looking at the success of Chandrayaan-2," pointed out Sivan. "Any learning will be shared with other countries," he added. Any learning could help with ongoing research countries have undertaken, primarily the ones on inhabiting the moon.

Unlike other parts, South Pole large volumes of water ice on this surface and any insight will help the scientific community.

Apart from studying water, which Chandrayaan -1 discovered, it will study minerals that might lend a better understanding of the earth’s satellite. It will also thermal conductivity and temperature gradient.
In addition, the mission will also carry NASA’s refro-reflectometer to measure the distance between the moon and earth.

Anything could go wrong before the soft landing

Explaining the steps, Sivan said, "In order to achieve the required location for soft landing in the (moon's) South Pole, Chandrayaan-2 has a unique requirement."

“For this, the inclination with the moon’s orbit should be 90 degrees with the South Pole," he added.

Right now the orbiter is in an elliptical orbit of 114 km perilune (closest point to the moon) and 18000 km apolune (farthest from the moon). This distance needs to 100 km, both perilune and apolune, before the lander and rover gets detached from the orbiter.

Here is where the challenge starts. Once the lander and rover composite de-orbits on September 4, it will revolve around the Moon at a distance of 35 km grazing the mountains for about three days.

Anything could go wrong in this time period. For one, the required inclination of 90 degree might be off by few degrees.

Sivan explained, "To reach 90 degree, the velocity of the vehicle should be 0.1 km per second. Even a change of 10 cm will result in a distortion of 7 degrees."

Though any adjustments can be done before landing, Sivan said, it comes at a cost. Any change burns more fuel, and that further limits the capacity for the orbiter and the lander movement, he said.

"Close to 60-70 kg of fuel has been set aside to take into account these distortions and requisite corrections," he added.

Once all this is accounted for comes the actual soft landing, which is completely autonomous. Sivan had described this "as the most terrifying few minutes for ISRO."

"There are lot of new things we are doing like new algorithm for the launch. But we have done a lot of simulations and are confident of the success," he pointed out.

Swathi Moorthy
first published: Aug 20, 2019 02:10 pm

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