Why ISRO chose 23 August for the landing of Chandrayaan-3

The Chandrayaan-3 achievement would make India the fourth country in the world — following the Soviet Union, the US, and China — to successfully achieve a gentle landing on the moon.

BySumit Jha

Published Aug 23, 2023 | 5:02 PMUpdatedAug 23, 2023 | 5:03 PM

Earlier, ISRO had said that the touchdown would take place at 5:47 pm on 23 August. (Supplied)

India is gearing up for a significant attempt at landing on the south pole of the Moon — an achievement no country was ever successful in — set to take place on Wednesday, August 23.

The Chandrayaan-3 spacecraft is aiming to land close to the southern pole of the moon at approximately 6.04 pm IST.

If successful, this achievement would make India the fourth country in the world — following the erstwhile Soviet Union, the US, and China — to successfully achieve a gentle landing on the moon.

Why did the Indian Space Research Organisation (ISRO) choose 23 August as the landing date?

Related: Chandrayaan-3 soft landing as planned at 6:04 pm on Wednesday

The significance of 23 August

ISRO chose 23 August as the landing date for the Lander Module (LM) of the Chandrayaan-3 on the moon for a smart reason.

It’s like planning a picnic on a sunny day instead of a cloudy one. The spacecraft needs sunlight to power its batteries and do its tasks.

Just like we plan trips considering factors like distance and weather, space missions also need careful planning.

Landing on the Moon has to have mandates like the site of the landing and the intentions of the spacecraft.

Chandrayaan-3 was programmed to land on 23 August because that’s when the Moon’s daytime starts towards its south pole. This timing would help the spacecraft use sunlight to charge its batteries and do its job.

The date, 23 August, marks the commencement of the lunar day — equivalent to 14 Earth days — on the Moon’s south pole.

Significance of the south pole area

ISRO chose the area near the south pole of the moon since it was where the Chandrayaan-1 mission discovered the presence of water molecules.

Chandrayaan-3’s lunar lander, along with its payloads and experiments, relies on solar power. Therefore, a landing during the moon’s daytime becomes crucial to ensure that the lander’s batteries are charged and its mission tasks can be performed.

It’s like getting the most out of a battery that lasts for two weeks. If we land at the start of the moon’s sunny period, Chandrayaan-3 can work for the entire two weeks, and that’s a smart move to get the most information and data from its mission.

The timing of space missions holds significant importance and is influenced by various elements like the launch site, the type of rocket used, the intended path of travel, the mission’s goals, and the ultimate destination.

In the context of lunar landings, specific criteria come into play, including factors like the chosen landing spot/area, the phenomena to be studied, and the capabilities of the lander vehicle.

Related: Russia out of race to the moon after Luna-25 crash

The alignment to the lunar day

The decision to schedule Chandrayaan-3’s landing to align with the beginning of the lunar day is a meticulous one, aiming to optimise the mission’s duration.

Given that a lunar day spans around 14 Earth days, initiating the landing process at this time guarantees that the lander can make the most of its full operational span of 14 Earth days.

This strategic planning approach empowers Chandrayaan-3 to make the most comprehensive scientific observations, carry out experiments, and accumulate valuable data throughout its active phase on the Moon’s surface.

Since one of the reasons for the failure of Chandrayaan-2 was the small 500 m x 500 m site identified for landing the spacecraft, the ISRO has identified a larger landing area for Chandrayaan-3.

ISRO chief S Somnath had said that instead of the success-based design in Chandrayaan-2, the space agency opted for a failure-based design in Chandrayaan-3.

“We expanded the area of landing from 500m x 500m to 4 km x 2.5 km. It can land anywhere, so it doesn’t limit you to target a specific point. It will target a specific point only in nominal conditions. So, if the performance is poor, it can land anywhere within that area,” Somanath said.

Related: Two key features — a Tamil connect and a scientific payload

Journey to the moon

14 July: LVM3 M4 vehicle successfully launches Chandrayaan-3 into orbit from Sriharikota in Andhra Pradesh. Chandrayaan-3 starts its journey into precise orbit.

15 July: First orbit-raising manoeuvre (Earthbound firing-1) successfully performed from ISTRAC/ISRO, Bengaluru. The spacecraft is in 41,762 km x 173 km orbit.

17 July: Second orbit-raising manoeuvre performed. Spacecraft is in 41,603 km x 226 km orbit.

22 July: Another orbit-raising manoeuvre completed using Earth-bound perigee firing.

25 July: ISRO performs one more orbit-raising manoeuvre. Spacecraft is in 71,351 km x 233 km orbit.

1 August: ISRO performs Translunar Injection successfully and inserts the spacecraft into translunar orbit. The orbit achieved is 288 km x 3,69,328 km.

5 August: Lunar-Orbit Insertion of Chandrayaan-3 performed successfully. The orbit achieved is 164 km x 18074 km, as intended.

6 August: ISRO performs the second Lunar Bound Phase (LBN). With this, the spacecraft is in a 170 km x 4313 km orbit around the Moon. The space agency released a video of the Moon as viewed by Chandrayaan-3 during lunar orbit insertion.

9 August: Chandrayaan-3’s orbit is reduced to 174 km x 1437 km after a manoeuvre is performed.

14 August: Mission is in orbit circularisation phase after another manoeuvre. The spacecraft is in a 151 km x 179 km orbit.

16 August: Spacecraft brought down to an orbit of 153 km x 163 km after firing is completed.

17 August: Lander module is successfully separated from the propulsion module.

19 August: ISRO performs de-boosting of the lander module to reduce its orbit. The lander module is in a 113 km x 157 km orbit around the Moon.

20 August: One more de-boosting or orbit reduction manoeuvre on the lander module is performed. The lander module is in a 25 km x 134 km orbit.

21 August: Chandrayaan-2 orbiter formally welcomes Chandrayaan-3 lander module saying Welcome, buddy!’. Two-way communication between the two is established. Mission Operations Complex (MOX) now has more ways to communicate with the lander module.

22 August: ISRO releases images of the Moon captured by the Lander Position Detection Camera (LPDC) of the Chandrayaan-3 mission from an altitude of about 70 km. Systems are undergoing regular checks. Smooth sailing is continuing.

23 August: Safe and soft landing of Chandrayaan-3’s lander module on the southern pole of the lunar surface expected at 6.04 pm.