Chandrayaan 3: Four Critical Phases for Vikram Lander | Will ISRO Postpone Touchdown

Chandrayaan 3: Four Critical Phases For Vikram Lander
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In a couple of hours from now, India will be on the verge of creating history. The whole world waits with baited breath as India’s lunar mission, Chandrayaan 3 nears its completion.  A touchdown of the Vikram Lander on the moon will make India the fourth country after the USA, Russia, and China to have achieved this feat. And the first country to have executed a soft landing on the Lunar South Pole. A big feather in the cap of ISRO and a proud moment for 1.4 billion Indians.

The Chandrayaan 3 lunar mission under the Chandrayaan program of ISRO commenced on July 14, 2023, when the LVM3 M4 rocket fired off from the Satish Dhawan Space Centre at Sriharikota, Andhra Pradesh. Covering a distance of approximately 3.8 lakh kilometers, Chandrayaan 3 entered the lunar orbit on August 5, 2023, and is scheduled to make a soft landing on the lunar South Pole on August 23, 2023, at 6.05 p.m. IST. Currently, the lander module Vikram is orbiting the moon in an elliptical orbit of 25 kilometers by 134 kilometers in diameter and is scheduled to begin a power descent starting at 5.45 p.m. IST, today.

However, as per the latest updates received from ISRO, there is a remote possibility of a shift in the landing date in case any anomalies are detected. ISRO, after careful introspection, is due to take the final call 3–4 hours before the scheduled landing time.

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Chandrayaan 3 Success Depends on Four Critical Phases

As per ISRO, the Vikram Lander is on course and scheduled to start its power descent approximately 45–50 minutes prior to it’s landing time. During the power descent, the Vikram Lander is scheduled to perform some critical maneuvering tasks. These phases can be broadly divided into four categories. 1. The Rough Breaking Phase; 2. The Altitude Hold Phase; 3. The Fine Breaking Phase; and 4. The Terminal Descent Phase. Each of these phases is interlinked, and the successful execution of each phase is critical to the success of the Chandrayaan 3 mission. Let’s briefly look at each phase and understand its importance.

Rough Breaking Phase: The Most Critical Phase for Vikram Lander

The first phase of the landing process is known as the Rough Breaking Phase which is the most critical of all phases. This phase plays a vital role in the landing process, where there is a shift in both the horizontal and vertical velocity of the lander. The complex tasks will be initiated when the Vikram Lander is approximately 30 kilometers from the surface of the moon.

The entire process will be executed in approximately 12 minutes, during which the height of the Lander will be reduced from 30 kilometers to 7.42 kilometers from the surface of the moon. In the meantime, Vikram will cover a horizontal distance of 713 kilometers towards the predesignated landing site. By the end of the Rough Breaking Phase the Vikram Lander should have a horizontal velocity of 358 meters per second and a vertical velocity of 61 meters per second before it moves on to the next phase.

The Altitude Hold Phase

The second phase is the Altitude Hold Phase which will last for approximately 10 seconds. The criticality of this phase will be in the axis change of the Vikram Lander from a horizontal to a vertical axis. In this phase, the Lander is due to cover a distance of 3.48 kilometers with further reductions in horizontal and vertical velocity. By the completion of this phase, the horizontal velocity would be reduced further from 358 meters per second to 336 meters per second, with a reduction of the vertical velocity from 61 meters per second to 59 meters per second.

The Fine Breaking Phase

The Fine Breaking Phase is the penultimate phase in the landing process. This phase will be executed in approximately 3 minutes, when the Vikram Lander moves into a complete vertical position with the landing legs pointing down towards the surface of the moon. In this phase, the lander is due to cover a distance of approximately 28.5 kilometers towards the designated landing site.

The altitude of the Lander will be drastically reduced from 6.8 kilometers to an altitude of 800 to 1000 meters above the surface of the moon. During this phase, ISRO scientists will run some verification tests to ascertain the nature of the terrain and steer the Lander clear of any rocks, boulders, or deep crevices for a safe landing. Once ISRO is satisfied with the findings, it will give the final go for the last stage in the landing process.

The Terminal Descent Phase

The last and final stage is the Terminal Descent Phase, where the Vikram lander will finally make a soft touchdown on the surface of the moon. The touchdown velocity of the Lander should not be more than 3 meters per second; otherwise, it would be considered a crash landing, with major damage to technical components. However, the optimal speed is set at 2 meters per second before touchdown.

But unlike its predecessor, the Chandrayaan 3 Lander has stronger legs with shock absorbers to withstand a maximum velocity of 3 meters per second. The lander also has the capability of handling a tilt of 12 degrees and still executing a safe landing. However, a tilt in excess of 12 degrees can result in a tip-off. Once the lander steadies itself on the moon’s surface, it will release the Pragyan Rover, which will navigate the lunar surface for traces of water and minerals and conduct other tests.

If everything goes as planned, India’s name will go down in history as the first country to have successfully executed a soft landing on the south pole of the moon. In the race for the moon, India was not the only contender. Russia’s moon mission, the Luna-25, was scheduled to make a soft landing on the moon on August 21, 2023, three days prior to Chandrayaan 3. Unfortunately, Russia’s moon mission took a major jolt when Luna-25 crashed on to the moon’s surface. With Russia out of the race the world focus is now on Chandrayaan 3.

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Can ISRO shift to Plan B? Postpone Landing Day for Vikram?

While the whole nation is busy in prayers, organizing science gatherings, and schools indulging students to watch live telecasts of Chandrayaan 3, India’s moon mission enters the most critical phase of its journey. So long, there were only two aspects to the outcome. By the nightfall of August 23, will India be celebrating the success of Chandrayan 3, or will there be another heartbreak as in the case of Chandrayaan 2?

Chandrayaan 2 did everything right, from takeoff to injection into the lunar orbit; only the Vikram lander failed to make it to the lunar surface. The visuals of then-ISRO chief K. Sivan breaking down and PM Modi comforting him are still fresh in our minds. Chandrayaan 3 is exactly at the same place where things went wrong for ISRO in 2019. Can ISRO pull it off this time? The whole world is watching.

The Two-Phase Landing Strategy for Vikram Lander

Recently, a new development has surfaced. As per the latest updates received from ISRO, a contingency plan is being looked into. In the event of any unforeseen complexities, the touchdown date for the Lander Module could be shifted to August 27, 2023. To ascertain the condition of the Lander Module and the mission’s current status, ISRO would conduct close monitoring and critical review meetings. Two to three hours prior to touchdown will be the most crucial phase, when ISRO has to make the toughest call. Whether to go for the landing or postpone it for another date.

A moon landing is quite different from an aircraft attempting a landing. An aircraft always has the option to abort a landing at the last moment if conditions are not suitable, but you don’t get that luxury in the case of lunar landings. You just get one shot at it, and if anything goes wrong, it’s mission over. ISRO Misson Control will make the final call three to four hours prior to touchdown time on whether to attempt the soft landing or not. ISRO is committed to mission success, and they always have a backup plan ready in case of any contingencies. 

A moon landing is quite different from an aircraft attempting a landing. An aircraft always has the option to abort a landing at the last moment if conditions are not suitable, but you don’t get that luxury in the case of lunar landings. You just get one shot at it, and if anything goes wrong, it’s mission over. ISRO Misson Control will make the final call three to four hours prior to touchdown time on whether to attempt the soft landing or not. ISRO is committed to mission success, and they always have a backup plan ready in case of any contingencies.

In case of any technical glitch, malfunction, or adverse weather condition on the moon’s surface, ISRO has the option to shift the landing date to August 27.  And if some last minute findings do compel ISRO to change dates, a new and safer landing site has been predesignated. With both the moon and orbiter in motion and relative velocity coming into play, it won’t be possible to land at the exact same spot on the second attempt. However, as per the latest updates received from ISRO, the Vikram Lander is right on track and geared up for a soft landing on August 23, 2023, at 6.04 p.m. IST. India’s Chandrayaan 3 mission is well and truly on course for success.


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