Exclusive: Chandrayaan-3's Big Upgrade To Tackle What Went Wrong Last Time

Armed with lessons learnt four years ago and equipped with more fuel and fortified safety measures, India's third lunar mission, Chandrayaan-3 is ready to make its leap towards the moon on Friday at 2:35 pm.

This comes as a follow-up mission after the hard landing of Chandrayaan-2 in September 2019 due to a software and hardware anomaly. In an interview with NDTV, ISRO Chairman S Somanath revealed how the space agency has learned from past failures and implemented changes for the upcoming mission.

"The main lacuna in the last Chandrayaa-2 mission was that there were off-nominal conditions that were initiated in the system. Everything was not nominal. And the craft was not able to handle the off-nominal condition for a safe landing," he said.

Mr Somanath explained that the new mission has been designed to land successfully even if certain elements fail. Several scenarios including sensor failure, engine failure, algorithm failure, and calculation failure were examined and measures developed to counteract them.

"The essential lesson is, in any space mission the focus should be on conditions of normality. So, how we address them and how we mitigate the possibilities of a failure in such an event," Mr Somanath said.

"We have added new instruments to handle failures, new algorithms to handle off-nominal situations, new approaches to soft land in case of not-availability, any such measurements and total uncertainty," he added.

According to him, the primary issues with Chandrayaan-2 were linked to the engines developing higher thrust than expected, leading to accumulated errors and fast turns that exceeded the software's expected rates. The 500m x 500m landing site also proved too small for the spacecraft's needs.

Chandrayaan-3 has been designed with these issues in mind, expanding the landing area to 4 km by 2.5 km. The spacecraft also carries more fuel and additional solar panels to ensure power generation regardless of its landing orientation.

"We also strengthened the lander in various ways, like increasing the propellant loading in the lander... added more of solar power generation capability... as to have more tolerance to non-orientation or wrong orientation of landing," Mr Somanath said.

"We added new sensors like the laser Doppler velocity emitter to handle or to measure the velocity of the craft in relation to the surface of the moon and have redundancies of measurements in addition to the already existing optical measurements on board," he said.

"Legs of the lander, though that's configuration remains the same, structurally it has been strengthened to handle almost one meter per second additional velocity also. So, that even if it has a hard landing, the possibility of survival could be higher," the ISRO chief added.

The space agency has also conducted a 24-hour "launch rehearsal" simulating the entire launch preparation and process for the upcoming mission. Chandrayaan-3 will launch aboard a Launch Vehicle Mark 3 (LVM3) from the spaceport at Sriharikota in Andhra Pradesh.

The mission's objectives include demonstrating safe landing and roving on the lunar surface, developing new technologies for inter-planetary missions, and continuing the scientific investigations initiated by previous missions. The orbiter from Chandrayaan-2, still in good health, will serve as a relay station for the mission.

Chandrayaan-3 will target a similar landing site as its predecessor, close to the moon's South Pole. This region is of interest due to the potential presence of water discovered by Chandrayaan-1.

Despite the setback with Chandrayaan-2, Mr Somanath expressed confidence in the upcoming mission. He said that the space agency had consulted experts, including those from the NASA's Jet Propulsion Laboratory (JPL) in California and Indian Academy and institutions, to ensure the success of Chandrayaan-3.

"We have brought in domain specialist and propulsion, control guide and electronic sensors and various flight mechanics, mathematics, and they sit together and review in hundreds of committees and reviews and everywhere there will be some suggestions and improvements," Mr Somnath said.