A nail-biting countdown for the descent of Chandrayaan-3’s lander began on Tuesday with India aiming to become the fourth country in the world to successfully land on the moon, and the first on the lunar south pole.
Senior scientists said they were confident of a successful landing of the Chandrayaan-3 lander module, Vikram, and the Indian Space Research Organisation (Isro) was performing the final checks for a successful touchdown as soon as the sun rises on the moon a little after 6pm IST on Wednesday.
Also read: What is ‘17 minutes of terror’ for Chandrayaan 3? Senior ISRO official explains
“Chandrayaan-3 Mission: The mission is on schedule. Systems are undergoing regular checks. Smooth sailing is continuing. The Mission Operations Complex (MOX) is buzzed with energy & excitement!,” the space agency said in a post on X on Tuesday.
Since India’s second lunar mission, Chandrayaan-2, crashed on the surface of moon on September 7, 2019, scientists at Isro have spent the last four years analysing each contingency and rectifying the errors of the last mission, strengthening the hardware and software of the craft, and have prepared for worst-case scenarios via simulations.
“We have accounted for all scenarios that can go wrong and have prepared a backup plan for that. Till now, all stages of the mission have gone as per plan, and we are confident that our lander Vikram will successfully land on the moon tomorrow,” Isro chairman S Somanath said.
Prime Minister Narendra Modi, who is in South Africa for the 15th BRICS Summit, could join the landing virtually, reports said citing officials.
Union minister for science and technology Jitendra Singh is scheduled to attend the landing virtually from Delhi.
After all final checks on Wednesday, Chandrayaan-3’s lander will identify its landing site which has been increased to an area of 4km x 2.5km from the 500m x 500m spot that was planned for its predecessor.
Thrusters will then start a controlled descent of the spacecraft around 5.45pm. Once the lander module reaches closer to the lunar surface, its speed will gradually reduce, its legs — which have also been engineered to be stronger compared to the Chandrayaan-2 lander — will extend out, and the craft will make a landing at around 6.04pm.
Following a successful touchdown, the lander’s flaps will open to reveal a ramp for the rover, Pragyaan, to roll out.
Once the rover is placed on the moon, it will click pictures of the lunar surface. The lander and rover will also take pictures of each other to ensure that there is communication between the two, and Isro’s base station to monitor the mission progress.
The indigenous lander module, propulsion module and rover on Chandrayaan-3 have the objective of developing and demonstrating new technologies for interplanetary missions.
The propulsion module separated from the craft to carry out independent experiments in the lunar orbit.
The lander, meanwhile, has the capability to “soft land” and deploy the rover which will carry out in-situ chemical analysis of the lunar surface during the course of its mobility. Both the lander and the rover are equipped with scientific payloads to carry out experiments.
The lander is carrying the Chandra’s Surface Thermophysical Experiment (ChaSTE) to measure the thermal conductivity and temperature; Instrument for Lunar Seismic Activity (ILSA) for measuring the seismicity around the landing site; Langmuir Probe (LP) to estimate the plasma density and its variations. A passive Laser Retroreflector Array from the National Aeronautics and Space Administration (Nasa) is also accommodated for lunar laser ranging studies.
The rover, on the other hand, has the payload of the Alpha Particle X-ray Spectrometer (APXS) and Laser Induced Breakdown Spectroscope (LIBS) for deriving the elemental composition in the vicinity of landing site.
While according to the initial plan, the experiments are expected to go on for 14 Earth days – one lunar day —the Isro chief on Monday told HT that there is a scope for an extended life of the solar-powered equipment if it gets recharged after the next lunar sunrise.
Changes from Chandrayaan-2
While Chandrayaan-2 could not make a soft landing on the moon, officials said the mission was a “part failure”, as the orbiter has continued to orbit the moon, providing critical data that has helped Isro prepare for the latest mission.
Ahead of the Chandrayaan-3 launch on July 14, an Isro official said, “We landed with a higher velocity—we call this a crash landing. But if you analyse the mission in its entirety, we have perfected the part of reaching up to the moon in earlier missions.”
A failure analysis report of the mission, prepared by Isro after the partial failure of Chandrayaan-2, highlighted that the five engines (these have been downsized to four for the latest mission) used for the reduction of velocity developed a higher thrust than was intended.
The plan was for the lander to lose most of its velocity at a distance of 400m from the lunar surface and start hovering above the landing spot to ensure a soft vertical descent. The high velocity, however, led to the crash.
For Chandrayaan-3, Isro has built a sturdier spacecraft with a higher fuel capacity to reduce the possibility of failure and to give the craft more flexibility to manoeuvre possible errors during landing.
Backup landing plans
While the best-case scenario that the agency has prepared for is a landing on Wednesday evening, scientists said that they have prepared for contingency plans in case the lander module is unable to reach the lunar surface.
The Isro chief said that the agency has a backup plan that will be explored for landing, in case it missed the first opportunity in the evening of August 23.
“The aim is to land in the initial period after the lunar sunrise so that the mission gets enough days to complete its experiments,” Somanath told HT. “The availability of sunlight is crucial to power the equipment.”
All modules on the craft are solar powered. The agency has, thus, planned the mission in a way that the craft lands at the time of lunar sunrise to allow 14 Earth days (one lunar day) for experiments.
Also read: Chandrayaan-3: How will Moon mission help boost India’s space sector? Details
“If it doesn’t land tomorrow owing to whatever factor, whether the health of the lander or a break in communication, we will attempt the landing again within 24-50 hours. Meanwhile, alternate landing sites will also be considered,” Somanath said.
If the descent is deemed risky, the landing could be deferred for a month till the next lunar sunrise, he added.
In that case, the craft will hover in its current orbit of 25km x 134km till next lunar sunrise, the scientist said.
Officials did not reveal details of Isro’s backup plan citing security reasons.