ISRO chairman S Somanath said on Tuesday that Chandrayaan-3 "is tilted 90 degrees, but it has to become vertical and the process of turning from horizontal to vertical is an interesting calculation".

The Indian Space Research Organisation (ISRO) has time and again exuded confidence in the 'failure-based design' that they have opted for for its third lunar mission — Chandrayaan-3 mission. In a virtual address on Tuesday, ISRO chairman S Somanath said the entire design of the lander ‘Vikram’ has been made in a manner that makes sure that it would be able to handle failures.

Somanath was presenting details of the Chandrayaan-3 mission during a talk on ‘Chandrayaan-3: Bharat’s Pride Space Mission’ hosted by the non-profit organisation Disha Bharat on Tuesday. Meanwhile, the failure-based design in Chandrayaan-3 focuses on what all can fail and how to protect it and ensure a successful landing.

“If everything fails, if all the sensors fail, nothing works, still it (Vikram) will make a landing. That’s how it has been designed -- provided that the propulsion system works well,” Somanath said.

In his address, Somanath emphasised the biggest challenge before the ISRO team in its latest lunar mission.

"Many failures it (Chandrayaan-3 lander) should be able to handle, given the algorithm work proper during vertical landing," Somanath said during a presentation. He added that the challenge before the ISRO is to make a horizontal ‘Vikram’ land vertically on the lunar surface.

"The Chandrayaan is tilted 90 degrees, but it has to become vertical and the process of turning from horizontal to vertical is an interesting calculation," he added.

The ISRO chief said once the lander separates from the orbiter, it will move horizontally. Through a series of maneuvers, it will be brought to a vertical stance in order to land safely on the Moon.

This exercise is crucial, as ISRO failed to get its lander to touch down safely on the Moon's surface during the Chandrayaan-2 mission. “The ability to transfer from horizontal to vertical direction is the trick we have to play here. Here only we had the problem last time,” Somanath said.

The other challenge is also to make sure that the fuel consumed is lesser, the distance calculations are correct and all the algorithms work properly, the ISRO chief said.

However, the ISRO team has made arrangements to ensure that Vikram makes an attempt to land property even if there are some variations in the calculations."

"We have ensured that the touchdown speed of even up to three metres per second it will not cause harm to Chandrayaam (3). It makes sure the vertical velocity is in limit so that it does not topple," Somanath explained.

Why is the soft landing of the lander important?

The ISRO chief said only if 'Vikram' lands softly, the rover can come out and "we can do scientific experiments". The final landing will involve a separation exercise.

Soft landings refers to successful landing of a spacecraft — when the craft touches down at a safe, slow, and controlled speed — without causing any damage to itself or to its payloads.

A successful soft landing on the surface of the Moon would make India the fourth country in the world to achieve such a significant technological capability.

"The successful soft landing is envisaged to serve as fore-runners for future landing missions and other technological progress in planetary exploration," the Department of Space said in a press release on August 3.

According to the ISRO, Chandrayaan-3 would attempt a soft landing on the moon's surface on August 23 after performing a series of maneuvers on August 9, 14, and 16 — reducing its orbit to 100 km x 100 km. It is expected to land on the Moon at 5.47 pm on August 23, 2023, India Today reported.

Chandrayaan-3 is a follow-on mission to Chandrayaan-2 to demonstrate end-to-end capability in safe landing and roving on the lunar surface.

It comprises an indigenous propulsion module, a lander module and a rover to develop and demonstrate new technologies required for inter-planetary missions.

The propulsion module will carry the lander and rover configuration till 100 km of lunar orbit. The propulsion module has a Spectro-polarimetry of Habitable Planet Earth (SHAPE) payload to study the spectral and polarimetric measurements of the earth from the lunar orbit.

The lander has the capability to soft land at a specified lunar site and deploy the rover that will carry out in-situ chemical analysis of the moon's surface during the course of its mobility.

The lander and the rover have scientific payloads to carry out experiments on the lunar surface.

The lander will have four payloads: Chandra’s Surface Thermo Physical Experiment (ChaSTE) will carry out the measurements of thermal properties of lunar surface near polar region.

RAMBHA-LP payload will measure the near surface plasma (ions and electrons) density and its changes with time; Laser Retroreflector Array from NASA for accurate positioning measurement of the lander on lunar surface by future orbiters; and Instrument for Lunar Seismic Activity.

The rover named ‘Pragyan’ will have three payloads: The Laser Induced Breakdown Spectroscope (LIBS) will determine the elemental composition of lunar soil and rocks around the lunar landing site.

The Alpha Particle X-Ray Spectrometer (APXS) payload will derive the chemical composition and infer mineralogical composition to further enhance our understanding of the lunar surface.

Spectro-polarimetry of Habitable Planet Earth (SHAPE) is an experimental payload in Pragyan to study the spectro-polarimetric signature of the habitable planet Earth in the near-infrared (NIR) wavelength range.