As Chandrayaan-3 and Luna 25 prepare to land on Moon, two questions

Subject: Science and technology

Section: Space technology

Context:

India’s Chandrayaan-3 and Russia’s Luna 25 are both in lunar orbit, preparing for a landing on the Moon next week. Luna 25 is expected to go first, on August 21, while Chandrayaan-3 is likely to touch down two days later, on August 23.

Details:

Both missions are aiming to land in a region where no spacecraft has gone before, near the South Pole of the Moon.
Since the landing of the then Soviet Union’s Luna 24 in 1976, only China has been able to land a spacecraft on the Moon — Chang’e 3 and Chang’e 4 in 2013 and 2018 respectively. India and Russia are both trying to make their first soft landing.

Why is Luna 25 Reaching the Moon Earlier than Chandrayaan-3?

Luna 25 rode on a powerful rocket to reach lunar orbit in just six days after launch on August 10.
Chandrayaan-3 took 23 days after launching on July 14, because ISRO still does not have a powerful enough rocket to go directly to lunar orbit.
Luna-25 has a direct trajectory route unlike Chandrayaan-3, that took a longer route to compensate for its lower fuel reserve
Luna 25’s lift-off mass of 1,750 kg is significantly lighter than Chandrayaan-3’s 3,900 kg, facilitating a quicker journey.

What determines the landing time of the two spacecraft?

August 23 is the beginning of daytime on the Moon.
- One lunar day is equivalent to about 14 days on Earth, when sunlight is continually available.
The instruments on Chandrayaan-3 have a life of just one lunar day, or 14 Earth days.
That is because they are solar-powered instruments, and require sunlight to remain operational.
- The Moon gets extremely cold during night time, well below minus 100 degree Celsius. Electronics not specifically designed to operate at such low temperatures can freeze and become non-functional.
To maximize the time for observations and experiments, it is crucial for Chandrayaan-3 to land at the beginning of the lunar day.
- If for some reason, it is unable to attempt the landing on August 23, another attempt is supposed to be made the next day.
- If that too is not feasible, it would wait for one full month– about 29 days– for the lunar day and lunar night to get over.
Luna 25 has no such restrictions.
- It too is solar powered, but it also has an onboard generator to provide heat and power to the instruments during night time.
- It has a life of a year, and the choice of its landing date is not dictated by how much Sun is shining on the Moon.

How far apart will the Indian and Russian missions land?

The selected site for Chandrayaan-3 is about 68 degree South latitude while that of Luna 25 is closer to 70 degree South.
All landings have so far happened in the equatorial region, mainly because this area gets the most sunlight.