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Tuesday, August 22, 2023

Chandrayaan-3: How Vikram Lander will perform a soft landing on the Moon? Why less likely to fail, understand the full math

Chandrayaan-3: How Vikram Lander will perform a soft landing on the Moon? Why less likely to fail, understand the full math

Chandrayaan-3 landing process: ISRO has brought Chandrayaan 3 close to the moon, how will it do the soft landing now? Why is the probability of failure less? Understand everything.

Chandrayaan 3 mission: When the Indian Space Research Organization's (ISRO) Chandrayaan-3 Vikram lander enters the final 15 minutes of its mission to soft land on the Moon on August 23, it will have to change its high-speed horizontal position, vertically – on the lunar surface. To facilitate gradual descent.

આ પણ વાંચો:- ચંદ્રયાન-3 નું લેન્ડિંગ લાઈવ જોવા અહીં ક્લિક કરો. 

With the final deboosting of the lander completed on Sunday (August 20) to reduce the Chandrayaan-3 lander's orbit to a 25 X 134 km orbit around the moon, the main focus is now on the final landing phase scheduled for Wednesday (August 23). Evening – The last 15 minutes (where Chandrayaan 2 mission failed to land) is the key to a successful mission.

In September 2019, the Chandrayaan 2 lander's attempt at an automated soft landing on the Moon failed, when the lander did not properly switch from horizontal to vertical, and crashed while entering the lunar surface. After a fine breaking phase at a height of 7.42 km above the surface”.

Rough breaking phase

Another important part of the Chandrayaan 3 landing is the simultaneous process of reducing the horizontal velocity of the Chandrayaan 3 lander from a limit of 1.68 km/s or 1680 m/s to nearly zero at an altitude of 30 km above the lunar surface. To facilitate a soft landing at a pre-determined location near the Moon's South Pole.

ISRO Chairman S Somnath said in a public address on August 9, “Currently Chandrayaan 3 is inclined to about 90 degrees (when the landing process starts on August 23 at 17.47 pm) but it needs to be vertical (for landing). This entire process of turning the lander from horizontal to vertical is a very interesting calculation mathematically. We have done many simulations. This is where we had the last problem (which caused Chandrayaan 2 to crash on the lunar surface on September 7, 2019).”

He said, “Transfer from horizontal position to vertical position is the trick we have to play here to achieve landing. We have to make sure that the fuel consumption is low, the distance calculation is correct and importantly, all the algorithms are working properly.”

Chandrayaan 2's landing in September 2019 was on track until about three minutes before the final "terminal descent phase", when the lander spun more than 410 degrees and deviated from its calibrated spin of 55 degrees to crash-land on the Moon.

While the Chandrayaan 3 lander's speed and direction are controlled by 12 onboard engines. The ISRO chairman said, “The lander's four engines are used to decelerate and eight smaller engines are also used to control the landing direction. The engine is throttleable and the thrust can be varied from 800 Newton to a lower value of approx. This engine can keep the lander moving on the Moon's gravity.”

The horizontal velocity at the beginning of the landing process which would be about 1.68 km/s or about 1680 m/s (the vertical velocity is zero at this stage) would have to be reduced to the first horizontal velocity of 358 m/s and 61 m/s. In the ideal “rough breaking phase” of 690 seconds, the lander descends from an altitude of 30 km (745.5 km from the landing site) to 7.42 km – while covering a total distance of 713.5 km, between the landing site and the lunar surface.

Let's understand more

When the lander reaches an altitude of 7.42 km above the lunar surface, it will enter an “attitude hold phase” lasting about 10 seconds, where the lander will first tilt from horizontal to vertical, covering a distance of 3.48 km. Where the altitude will decrease from 7.42 km to 6.8 km and the speed will be 336 m/s (horizontal) and 59 m/s (vertical).

Best great breaking stage

In the third phase of the lunar surface landing, known as the “fine breaking phase”, which lasts about 175 seconds, the lander will become completely vertical during the final 28.52 km distance from the landing site. Height will be less than 6.8. Km to 800/1000 m and nominal speed to zero m/s.

Somnath said, “There will be rough braking from 30 km to 7.42 km (altitude) and attitude hold phase at 7.42 km, where some instruments will calculate; At 800 or 1300 meters (altitude) it will start checking the sensors, at 150 meters (altitude) it will check the threat and decide, whether it should descend vertically there, or go back to a maximum range of 150 meters. To avoid any rocks or craters on the lunar surface.”

Terminal landing stage

The Chandrayaan 2 lander was between the second “attitude hold phase” and the third “fine breaking phase” when it lost control and crashed before entering the final “terminal descent phase”.

ISRO has now used the study of the Chandrayaan 2 lander failure to improve the chances of landing Chandrayaan 3.

For example, Chandrayaan 2 used a first-order automatic guidance system in the first rough braking phase, but Chandrayaan 3 is using a second-order guidance system. In Chandrayaan 3, instant thrust regulation is also used in the rough braking phase.

In Chandrayaan 3, the thrust demand during the second attitude hold phase is higher at 740 × 4 N instead of 400 × 4 N in Chandrayaan 2 to ensure thrust continuity at the beginning of the second phase of landing. Simply put, the new technology systems will facilitate thrust (speed) and angle constancy (control) for the lander, as it can be moved from a horizontal to a vertical position.

ISRO Chairman Somnath said, “Extensive simulations have been done, the guidance design has been changed, a lot of algorithms have been put together to ensure that the required perturbations are achieved at all these stages. Even if there is a nominal number of variations, the lander will attempt a vertical landing.”

He said, “Even if all the sensors fail, if everything fails, the landing will happen, as long as the propulsion system works well. It is designed that way. Even if two engines fail, the lander will be able to land this time. It is designed in such a way, that it is able to handle multiple problems and failures as well. If the algorithm works well, we should be able to do a vertical landing.”

The lander can descend at a maximum speed of 3 m/s (10.8 km/h) without endangering the onboard equipment, but the maximum speed is about 2 m/s (7.2 km/h). The lander can also tilt up to 12 degrees for safe landing.

Somnath said, “Though the speed of 3 m/s seems low, if a man falls at this speed, all his bones will break. Although this is not a low speed, it is a speed that we can guarantee with our sensors and measurements. Even trying to land at very low speed requires more fuel and theoretically requires some speed to touch down and is known as 1 m/s. However, our system is designed to handle speeds up to 3 m/s.”

An ISRO chairman recently said, “Chandrayaan 2 was designed to land at a speed of 2 m/s (7.2 km/h) with little boost distance, but we have now increased the speed limit for landing. We have also built energy absorption capabilities.”

આ પણ વાંચો:- ચંદ્રયાન-3 નું લેન્ડિંગ લાઈવ જોવા અહીં ક્લિક કરો. 

“We aim for a soft and safe landing. In case of an accident then none of the equipment can work. There are five experiments on the mission, three on the lander and two on the rover. These experiments will only work with a safe and soft landing.

Once the lander settles on the lunar surface, it will release a rover, which it is carrying, to take pictures of the lunar surface and conduct experiments with two onboard instruments.

In September 2019, during the second of the four stages of Chandrayaan 2's landing process, an anomaly appeared in the computer system in the mission control room, but since the lander was autonomous, ISRO scientists could not intervene to fix it. The mode is using data acquired in its system prior to the start of a powered descent to the lunar surface.

With communications on the failed lander supplying data on its performance up to 400 meters before the crash on the lunar surface, ISRO is now confident that the mistakes made in Chandrayaan 2 have been rectified to allow Chandrayaan-3 to make a soft landing.

“The second and final deboosting operation successfully reduced the LM orbit to 25 km x 134 km. The module will now undergo internal checks and await sunrise at the designated landing site. The powered descent is expected to begin on August 23, 2023 at approximately 17.45 hours. IST,” ISRO said after lowering Chandrayaan 3 before its final orbital landing on Sunday.

Understand more simply

India's Chandrayaan 3 mission is very close to being successful. ISRO can write a new chapter on August 23 at 6.04 pm. No one has ever landed on the Moon's South Pole, so Chandrayaan 3 could become the first country to do so. Now this time the possibility of India's success is also considered more. Learning from past mistakes has been done, along with some changes that are making ISRO even more exciting.

Why is Chandrayaan 3 more accurate?

It is worth mentioning that at this time all the pictures of the moon sent by Chandrayaan 3 have been captured by the camera mounted on Vikram. Now the camera is not only doing the job of taking pictures, but from those pictures are also getting continuous updates about the current position of the moon. In fact, ISRO will try to do a soft landing of Vikram at any cost, now it is possible only when all the conditions are favorable.

Here it is important to understand that ISRO has a SAC center whose job is to check that everything is going well in the mission. Deep study of scientists is also done by this team. It will happen that, if any error or mistake is noticed, it will be vigilantly corrected by these people.

How will the error be caught already?

This could not happen during Chandrayaan 2, ISRO lost contact and Vikram made a hard landing on the lunar surface. Russia's Luna 25 also crashed this way because it lost contact in its final stage and entered the wrong orbit. But Chandrayaan 3 has not made any mistakes yet. It seems ready to land at the right time. All the phases have been successfully completed so far. Final deboosting is also done, now as the lander approaches the moon as explained above, its speed and its movement horizontally and vertically will be controlled, and it will land successfully.

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